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Integrated Intermediate System-to-Intermediate System (IS-IS), Internet Protocol Version 4 (IPv4), is a standards-based Interior Gateway Protocol (IGP). The Cisco software implements the IP routing capabilities described in International Organization for Standardization (ISO)/International Engineering Consortium (IEC) 10589 and RFC 1195, and adds the standard extensions for single topology and multitopology IS-IS for IP Version 6 (IPv6).
This module describes how to implement IS-IS (IPv4 and IPv6) on your Cisco IOS XR network.
You must be in a user group associated with a task group that includes the proper task IDs. The command reference guides include the task IDs required for each command. If you suspect user group assignment is preventing you from using a command, contact your AAA administrator for assistance.
Multiple IS-IS instances can exist on the same physical interface. However, you must configure different instance-id for every instance that shares the same physical interface.
Alternatively, you can also create dot1q sub-interfaces and configure each dot1q sub-interface to different IS-IS instances.
 Note |
Users can configure the no max-metric command only with levels 1 or 2, that is, no max-metric level {1|2} in order to view the result in the output of the show configuration command. Else, the maximum metric configuration is not displayed in the output. This behavior is observed before committing the configuration to the router. |
To implement IS-IS you need to understand the following concepts:
Small IS-IS networks are typically built as a single area that includes all routers in the network. As the network grows larger, it may be reorganized into a backbone area made up of the connected set of all Level 2 routers from all areas, which is in turn connected to local areas. Within a local area, routers know how to reach all system IDs. Between areas, routers know how to reach the backbone, and the backbone routers know how to reach other areas.
The IS-IS routing protocol supports the configuration of backbone Level 2 and Level 1 areas and the necessary support for moving routing information between the areas. Routers establish Level 1 adjacencies to perform routing within a local area (intra-area routing). Routers establish Level 2 adjacencies to perform routing between Level 1 areas (interarea routing).
Each IS-IS instance can support either a single Level 1 or Level 2 area, or one of each. By default, all IS-IS instances automatically support Level 1 and Level 2 routing. You can change the level of routing to be performed by a particular routing instance using the is-type command.
Multiple IS-IS instances can exist on the same physical interface. However, you must configure different instance-id for every instance that shares the same physical interface.
Alternatively, you can also create dot1q sub-interfaces and configure each dot1q sub-interface to different IS-IS instances.
The IS-IS Max Metric on Startup feature allows IS-IS to advertise the maximum metric during the start-up phase. The feature allows the advertisement until either BGP converges or the specified start-up timer expires.
When you configure a router with maximum metric value on start-up, IS-IS advertises the maximum metric value for IS-IS links. IS-IS also advertises the prefixes that originated from the routers. This configuration makes the neighboring routers use this router as a transit-node of last resort. The router advertises the maximum metric only during the start-up phase when the routing table has not converged. The router advertises the normal metric values when the start-up timer expires or when the router receives the BGP converge signal. You can set maximum metric for default routes, SRv6 locator, or redistributed prefixes.
For narrow metrics, the maximum metric value is 63; for wide metrics, the maximum metric value is 16777214.
Router(config)# router isis 1
Router(config-isis)# max-metric level 2
Router(config-isis)# is-type level-2-only
Router(config-isis)# net 49.0001.0000.0000.0100.00
Router(config-isis)# nsr
Router(config-isis)# nsf cisco
Router(config-isis)# address-family ipv4 unicast
Router(config-isis-af)# metric-style wide
Router(config-isis-af)# mpls traffic-eng level-2-only
Router(config-isis-af)# mpls traffic-eng router-id Loopback 0
Router(config-isis-af)# default-information originate
Router(config-isis-af)# redistribute static
Router(config-isis-af)# exit
Router(config-isis)# address-family ipv6 unicast
Router(config-isis-af)# metric-style wide
Router(config-isis-af)# srv6
Router(config-isis-af)# locator abc
Router(config-isis-af)# exit
Router(config-isis)# interface Loopback 0
Router(config-isis-if)# address-family ipv4 unicast
Router(config-isis-if-af)# exit
Router(config-isis)# address-family ipv6 unicast
Router(config-isis-af)# exit
Router(config-isis)# interface GigabitEthernet0/0/0/2
Router(config-isis-if)# address-family ipv4 unicast
Router(config-isis-if-af)# exit
Router(config-isis-if)# address-family ipv6 unicast
router isis 1
max-metric on-startup wait-for-bgp default-route external interlevel srv6-locator level 2
is-type level-2-only
net 49.0001.0000.0000.0100.00
nsr
nsf cisco
address-family ipv4 unicast
metric-style wide
mpls traffic-eng level-2-only
mpls traffic-eng router-id Loopback0
default-information originate
redistribute static
!
address-family ipv6 unicast
metric-style wide
srv6
locator abc
!
!
!
interface Loopback0
address-family ipv4 unicast
!
address-family ipv6 unicast
!
!
interface GigabitEthernet0/0/0/2
address-family ipv4 unicast
!
address-family ipv6 unicast
!
!
!
The Cisco IOS XR implementation of IS-IS conforms to the IS-IS Version 2 specifications detailed in RFC 1195 and the IPv6 IS-IS functionality based on the Internet Engineering Task Force (IETF) IS-IS Working Group draft-ietf-isis-ipv6.txt document.
The following list outlines key features supported in the Cisco IOS XR implementation:
Single topology IPv6
Multitopology
Nonstop forwarding (NSF), both Cisco proprietary and IETF
Three-way handshake
Mesh groups
Multiple IS-IS instances
Configuration of a broadcast medium connecting two networking devices as a point-to-point link
Fast-flooding with different threads handling flooding and shortest path first (SPF).
Note |
For information on IS-IS support for Bidirectional Forwarding Detection (BFD), see Interface and Hardware Component Configuration Guide for Cisco ASR 9000 Series Routers and Interface and Hardware Component Command Reference for Cisco ASR 9000 Series Routers. |
Cisco IOS XR groups all of the IS-IS configuration in router IS-IS configuration mode, including the portion of the interface configurations associated with IS-IS. To display the IS-IS configuration in its entirety, use the show running router isis command. The command output displays the running configuration for all configured IS-IS instances, including the interface assignments and interface attributes.
The following sections show how to enter each of the configuration modes. From a mode, you can enter the ? command to display the commands available in that mode.
The following example shows how to enter router configuration mode:
RP/0/RSP0/CPU0:router# configuration
RP/0/RSP0/CPU0:router(config)# router isis isp
RP/0/RSP0/CPU0:router(config-isis)#
The following example shows how to enter router address family configuration mode:
RP/0/RSP0/CPU0:router(config)# router isis isp
RP/0/RSP0/CPU0:router(config-isis)# address-family
ipv4 u
nicast
RP/0/RSP0/CPU0:router(config-isis-af)#
The following example shows how to enter interface configuration mode:
RP/0/RSP0/CPU0:router(config)# router isis isp
RP/0/RSP0/CPU0:router(config-isis)# interface GigabitEthernet 0
/3/0/0
RP/0/RSP0/CPU0:router(config-isis-if)#
The following example shows how to enter interface address family configuration mode:
RP/0/RSP0/CPU0:router(config)# router isis isp
RP/0/RSP0/CPU0:router(config-isis)# interface
GigabitEthernet 0 /3/0/0
RP/0/RSP0/CPU0:router(config-isis-if)# address-family ipv4 unicast
RP/0/RSP0/CPU0:router(config-isis-if-af)#
IS-IS interfaces can be configured as one of the following types:
Active—advertises connected prefixes and forms adjacencies. This is the default for interfaces.
Passive—advertises connected prefixes but does not form adjacencies. The passive command is used to configure interfaces as passive. Passive interfaces should be used sparingly for important prefixes such as loopback addresses that need to be injected into the IS-IS domain. If many connected prefixes need to be advertised then the redistribution of connected routes with the appropriate policy should be used instead.
Suppressed—does not advertise connected prefixes but forms adjacencies. The suppress command is used to configure interfaces as suppressed.
Shutdown—does not advertise connected prefixes and does not form adjacencies. The shutdown command is used to disable interfaces without removing the IS-IS configuration.
The software supports multitopology for IPv6 IS-IS unless single topology is explicitly configured in IPv6 address-family configuration mode.
Note |
IS-IS supports IP routing and not Open Systems Interconnection (OSI) Connectionless Network Service (CLNS) routing. |
By default, IPv6 routing is disabled in the software. To enable IPv6 routing, you must assign IPv6 addresses to individual interfaces in the router using the ipv6 enable or ipv6 address command. See the Network Stack IPv4 and IPv6 Commands on Cisco ASR 9000 Series Router module of IP Addresses and Services Command Reference for Cisco ASR 9000 Series Routers.
Limiting link-state packets (LSP) may be desirable in certain “meshy” network topologies. An example of such a network might be a highly redundant one such as a fully meshed set of point-to-point links over a nonbroadcast multiaccess (NBMA) transport. In such networks, full LSP flooding can limit network scalability. One way to restrict the size of the flooding domain is to introduce hierarchy by using multiple Level 1 areas and a Level 2 area. However, two other techniques can be used instead of or with hierarchy: Block flooding on specific interfaces and configure mesh groups.
Both techniques operate by restricting the flooding of LSPs in some fashion. A direct consequence is that although scalability of the network is improved, the reliability of the network (in the face of failures) is reduced because a series of failures may prevent LSPs from being flooded throughout the network, even though links exist that would allow flooding if blocking or mesh groups had not restricted their use. In such a case, the link-state databases of different routers in the network may no longer be synchronized. Consequences such as persistent forwarding loops can ensue. For this reason, we recommend that blocking or mesh groups be used only if specifically required, and then only after careful network design.
With this technique, certain interfaces are blocked from being used for flooding LSPs, but the remaining interfaces operate normally for flooding. This technique is simple to understand and configure, but may be more difficult to maintain and more error prone than mesh groups in the long run. The flooding topology that IS-IS uses is fine-tuned rather than restricted. Restricting the topology too much (blocking too many interfaces) makes the network unreliable in the face of failures. Restricting the topology too little (blocking too few interfaces) may fail to achieve the desired scalability.
To improve the robustness of the network in the event that all nonblocked interfaces drop, use the csnp-interval command in interface configuration mode to force periodic complete sequence number PDUs (CSNPs) packets to be used on blocked point-to-point links. The use of periodic CSNPs enables the network to become synchronized.
Configuring mesh groups (a set of interfaces on a router) can help to limit flooding. All routers reachable over the interfaces in a particular mesh group are assumed to be densely connected with each router having at least one link to every other router. Many links can fail without isolating one or more routers from the network.
In normal flooding, a new LSP is received on an interface and is flooded out over all other interfaces on the router. With mesh groups, when a new LSP is received over an interface that is part of a mesh group, the new LSP is not flooded over the other interfaces that are part of that mesh group.
By default, the router sends a periodic LSP refresh every 15 minutes. LSPs remain in a database for 20 minutes by default. If they are not refreshed by that time, they are deleted. You can change the LSP refresh interval or maximum LSP lifetime. The LSP interval should be less than the LSP lifetime or else LSPs time out before they are refreshed. In the absence of a configured refresh interval, the software adjusts the LSP refresh interval, if necessary, to prevent the LSPs from timing out.
The Minimum Remaining Lifetime feature prevents premature purging and unnecessary flooding of LSPs. If the Remaining Lifetime field gets corrupted during flooding, this corruption is undetectable. The consequences of such corruption depend on how the Remaining Lifetime value is altered. This feature resolves this problem by enabling IS-IS to reset the Remaining Lifetime value of the received LSP, to the maximum LSP lifetime. By default, the maximum LSP lifetime is configured as 1200 seconds and you can configure it to a different value using the max-lsp-lifetime seconds command. This action ensures that whatever be the value of Remaining Lifetime that is received, a system other than the originator of an LSP will never purge the LSP, until the LSP has existed in the database at least for maximum LSP lifetime.
If the remaining lifetime for the LSP reaches 0, the LSP is kept in the link state database for an additional 60 seconds. This additional lifetime is known as Zero Age Lifetime. If the corresponding router does not update the LSP even after the Zero Age Lifetime, the LSP is deleted from the link state database.
The Remaining Lifetime field is also useful in identifying a problem in the network. If the received LSP lifetime value is less than the Zero Age Lifetime, which is 60 seconds, IS-IS generates an error message indicating that it’s a corrupted lifetime event. The sample error message is as follows:
Dec 14 15:36:45.663 : isis[1011]: RECV L2 LSP 1111.1111.1112.03-00 from 1111.1111.1112.03:
possible corrupted lifetime 59 secs for L2 lsp 1111.1111.1112.03-00 from SNPA 02e9.4522.5326 detected.IS-IS saves the received remaining lifetime value in LSP database. The value is shown in the show isis database command output under the Rcvd field.
For more information about the show isis database command, see IS-IS Commands Chapter of the Routing Command Reference for Cisco ASR 9000 Series Routers.
Single-topology IPv6 support on Cisco IOS XR software software allows IS-IS for IPv6 to be configured on interfaces along with an IPv4 network protocol. All interfaces must be configured with the identical set of network protocols, and all routers in the IS-IS area (for Level 1 routing) or the domain (for Level 2 routing) must support the identical set of network layer protocols on all interfaces.
In single-topology mode, IPv6 topologies work with both narrow and wide metric styles in IPv4 unicast topology. During single-topology operation, one shortest path first (SPF) computation for each level is used to compute both IPv4 and IPv6 routes. Using a single SPF is possible because both IPv4 IS-IS and IPv6 IS-IS routing protocols share a common link topology.
Multitopology IPv6 for IS-IS assumes that multitopology support is required as soon as it detects interfaces configured for both IPv6 and IPv4 within the IS-IS stanza.
Because multitopology is the default behavior in the software, you must explicitly configure IPv6 to use the same topology as IPv4 to enable single-topology IPv6. Configure the single-topology command in IPv6 router address family configuration submode of the IS-IS router stanza.
The following example shows multitopology IS-IS being configured in IPv6.
router isis isp
net 49.0000.0000.0001.00
interface POS0/3/0/0
address-family ipv6 unicast
metric-style wide level 1
exit
!
interface POS0/3/0/0
ipv6 address 2001::1/64
Authentication is available to limit the establishment of adjacencies by using the hello-password command, and to limit the exchange of LSPs by using the lsp-password command.
IS-IS supports plain-text authentication, which does not provide security against unauthorized users. Plain-text authentication allows you to configure a password to prevent unauthorized networking devices from forming adjacencies with the router. The password is exchanged as plain text and is potentially visible to an agent able to view the IS-IS packets.
When an HMAC-MD5 password is configured, the password is never sent over the network and is instead used to calculate a cryptographic checksum to ensure the integrity of the exchanged data.
IS-IS stores a configured password using simple encryption. However, the plain-text form of the password is used in LSPs, sequence number protocols (SNPs), and hello packets, which would be visible to a process that can view IS-IS packets. The passwords can be entered in plain text (clear) or encrypted form.
To set the domain password, configure the lsp-password command for Level 2; to set the area password, configure the lsp-password command for Level 1.
The keychain feature allows IS-IS to reference configured keychains. IS-IS key chains enable hello and LSP keychain authentication. Keychains can be configured at the router level (in the case of the lsp-password command) and at the interface level (in the case of the hello-password command) within IS-IS. These commands reference the global keychain configuration and instruct the IS-IS protocol to obtain security parameters from the global set of configured keychains.
IS-IS is able to use the keychain to implement hitless key rollover for authentication. ey rollover specification is time based, and in the event of clock skew between the peers, the rollover process is impacted. The configurable tolerance specification allows for the accept window to be extended (before and after) by that margin. This accept window facilitates a hitless key rollover for applications (for example, routing and management protocols).
Note |
If you configure domain authentication on a router, it rejects the limiting link-state packets (LSPs) from routers on which domain authentication is not configured. On the other hand, a router on which domain authentication is configured accepts the LSPs from routers on which domain authentication is configured. |
See Cisco ASR 9000 Series Aggregation Services Router System Security Guide for information on keychain management.
Purge Originator Identification TLV for IS-IS defines a type, length, and value (TLV) that can be added to the purges, to record the system ID of the IS that had initiated the purge.
If an IS generates a purge, this TLV is included in the purge, which also has the system ID of the IS. If an IS receives a purge, the Link State Protocol Data Unit (LSP) flooding does not change the LSP contents, and the TLV is propagated with the purge itself. If an IS receives a purge that does not include this TLV, it adds this TLV with both its own system ID and the system ID of the IS from which it received the purge. This allows the IS that receives this purge to log the system ID of the originator, or the upstream source of the purge. This makes it easier to locate the origin of the purge and its cause. This TLV is also helpful in lab environments.
If you are using cryptographic authentication, then the enable-poi keyword in lsp-password command must be enabled to insert the Purge Originator Identification (POI). If you are not using cryptographic authentication, then the POI is inserted by default.
For more information on configuring Purge Originator Identification feature, see Step 3 of the Configuring Authentication for IS-IS section.
For more information about Purge Originator Identification, see the RFC6232 Purge Originator Identification TLV for IS-IS.
On Cisco IOS XR software, IS-IS NSF minimizes the amount of time a network is unavailable to its users following the restart of the IS-IS process.
When the IS-IS process restarts, all routing peers of that device usually detect that the device went down and then came back up. This transition results in what is called a routing flap, which could spread across multiple routing domains. Routing flaps caused by routing restarts create routing instabilities, which are detrimental to the overall network performance. NSF helps to suppress routing flaps, thus reducing network instability.
NSF allows for the forwarding of data packets to continue along known routes while the routing protocol information is being restored following the process restarts. When the NSF feature is configured, peer networking devices do not experience routing flaps. To preserve routing across RP failover events, NSR must be configured in addition to NSF.
When the Cisco IOS XR router running IS-IS routing performs the process restarts, the router must perform two tasks to resynchronize its link-state database with that of its IS-IS neighbors. First, it must relearn the available IS-IS neighbors on the network without causing a reset of the neighbor relationship. Second, it must reacquire the contents of the link-state database for the network.
The IS-IS NSF feature offers two options when configuring NSF:
IETF NSF
Cisco NSF
If neighbor routers on a network segment are NSF-aware, meaning that they are running a software version that supports RFC5306, they assist a router configured with nsf ietf command that is restarting. IETF NSF enables the neighbor routers provide adjacency and link-state information to help rebuild the routing information following a failover.
In Cisco IOS XR software, Cisco NSF checkpoints (stores persistently) all the state necessary to recover from a restart without requiring any special cooperation from neighboring routers. The state is recovered from the neighboring routers, but only using the standard features of the IS-IS routing protocol. This capability makes Cisco NSF suitable for use in networks in which other routers have not used the IETF standard implementation of NSF.
Note |
If you configure IETF NSF on the Cisco IOS XR router and a neighbor router does not support IETF NSF, the affected adjacencies flap, but nonstop forwarding is maintained to all neighbors that do support IETF NSF. A restart reverts to a cold start if no neighbors support IETF NSF. |
Note |
Currently, a user can configure an aggressive hello-interval (lower than the default of 10 seconds for peer-to-peer session). But, if NSF is configured as a recovery for RP switchover, the default hello interval has to be used so that the sessions do not run into the risk of flapping during switchover. Using LAN adjacencies in high availability (HA) scenarios is not recommended, since there is no designated intermediate system (DIS) redundancy in the protocol and traffic will either drop or be rerouted temporarily during DIS re-election. |
Non Stop Routing (NSR) suppresses IS-IS routing changes for devices with redundant route processors during processor switchover events (RP failover or ISSU), reducing network instability and downtime. When Non Stop Routing is used, switching from the active to standby RP have no impact on the other IS-IS routers in the network. All information needed to continue the routing protocol peering state is transferred to the standby processor prior to the switchover, so it can continue immediately upon a switchover.
To preserve routing across process restarts, NSF must be configured in addition to NSR.
The IS-IS BFD-Enabled TLV feature allows you to add a BFD TLV into IS-IS Hello (IIH) message to establish BFD session before IS-IS adjacency is established.
Prior to Release 7.0.1, routers in a network do not establish a BFD session before they establish IS-IS adjacency among them. This approach was prone to certain failures. For example, in a network containing three routers R1, R2 and R3, router R1 has neighbors routers R2 and R3. Router R2 does not support BFD. Router R1 establishes IS-IS adjacency with routers R2 and R3, but it establishes a BFD session only with R3. BFD is meant for protecting IP forwarding and IS-IS adjacency does not send or receive IS-IS Hellos (IIHs) messages using IP forwarding. When router R3 experiences an IP forwarding failure, it might send and receive IS-IS Hello messages. When router R1 starts or restarts it incorrectly infers that router R3 does not support BFD, and establishes adjacency with R3. This could cause router R1 to incorrectly forward IP traffic through router R3. Starting with Release 7.0.1, a router that supports IS-IS advertises that BFD has been enabled on a particular interface. When sending IIH messages on a BFD-enabled interface, a router includes the BFD-enabled type-length-value (TLV) in its IIH. TLV contains Multi-Topology Identifier (MTID) and Network Layer Protocol Identifier (NLPID) pairs which indicate the BFD-enabled topologies and protocols. On receiving the BFD-enabled TLV from a neighbor, the router confirms that BFD is enabled on the IS-IS interface of the neighbor and hence IS-IS adjacency does not fully establish until BFD session is established.
This feature complies with RFC 6213.
Perform the following steps to configure the IS-IS BFD-enabled TLV feature.
Router# config
Router#(config)# router isis core
Router#(config-isis)# net 49.0001.0000.0000.0066.00
Router#(config-isis)# address-family ipv4 unicast
Router#(config-isis-af)# exit
Router#(config-isis)# address-family ipv6 unicast
Router#(config-isis-af)# metric-style wide
Router#(config-isis-af)# exit
Router#(config-isis)# interface GigabitEthernet 0/0/0/1
Router#(config-isis-if)# bfd fast-detect ipv4
Router#(config-isis-if)# bfd fast-detect ipv6
Router#(config-isis-if)# address-family ipv4 unicast
Router#(config-isis-af)# exit
Router#(config-isis)# address-family ipv6 unicast
Router#(config-isis-af)# commit
This section shows the running configuration of the IS-IS BFD-enabled TLV feature.
router isis core
net 49.0001.0000.0000.0066.00
address-family ipv4 unicast
!
address-family ipv6 unicast
metric-style wide
!
interface GigabitEthernet0/0/0/1
bfd fast-detect ipv4
bfd fast-detect ipv6
address-family ipv4 unicast
!
address-family ipv6 unicast
Verify the IS-IS BFD-enabled TLV feature.
Router# show isis adjacency
Fri Jun 21 01:04:22.399 UTC
IS-IS srv6 Level-1 adjacencies:
System Id Interface SNPA State Hold Changed NSF IPv4 IPv6
BFD BFD
P2-Fretta Te0/0/0/0 008a.96f4.9c00 Up 9 02:13:07 Yes None None
R4 Gi0/0/0/1 008a.9670.1800 Up 7 00:06:31 Yes Up Up
Router# show isis adjacency gigabitEthernet 0/0/0/1 detail
Fri Jun 21 01:06:02.257 UTC
IS-IS srv6 Level-1 adjacencies:
System Id Interface SNPA State Hold Changed NSF IPv4 IPv6
BFD BFD
R4 Gi0/0/0/1 008a.9670.1800 Up 9 00:08:11 Yes Up Up
Area Address: 49.0001
Neighbor IPv4 Address: 64.64.64.4*
Neighbor IPv6 Address: fe80::28a:96ff:fe70:1800*
Non-FRR END.X SID: cafe:0:0:a6:13b::/128 End.X (PSP), Algorithm 0
DIS Priority: 64
Local Priority: 64
Neighbor Priority: 64 (DIS)
Topology: IPv4 Unicast
Topology: IPv6 Unicast
Neighbor BFD TLV: MT-0:IPv4 MT-2:IPv6 << MT-2 indicates IPv6 for multi-topology and MT-0 indicates IPv6 for single-topology
BFD Status: BFD Required, Neighbor Useable << BFD is required status is displyed only if BFD has been enabled on both side of the link.
bfd fast-detect
show isis adjacency
The IS-IS Restart Signaling Support feature enables a restarting router to signal to its neighbors that it is restarting. This signaling allows neighboring routers to reestablish their adjacencies without going through the down state. At the same time, the neighboring routers initiate the synchronization of the database.
When an IS-IS router restarts, there is a temporary disruption of routing due to events in both the restarting router and the neighbors of the restarting router. The router that has restarted computes its own routes before it synchronizes the database with its neighbors.
The restarting router sends Suppress Adjacency (SA) advertisement toward the neighbor. The restarting router sends Intermediate-to-Intermediate Hello (IIH) messages to its neighbor to suppress the advertisement of the adjacency until the router is able to propagate newer versions of LSPs. The neighbor continues to suppress the advertisement of adjacency until it receives the SA bit clear message.
The IS-IS Restart Signaling Support conforms to the specifications detailed in RFC 5306.
The Reverse Metric Support feature allows you to move the traffic either from a point-to-point or multi-access LAN interface during network maintenance or other operational requirements. You can enable this feature using higher reverse metric value toward the signaling IS-IS router. The IS-IS router advertises reverse metric value in an IS-IS Hello (IIH) message to an adjacent node on a point-to-point or multi-access LAN link. This allows you to provision reverse metric value on a single node and shift the traffic from that link to alternate and viable paths.
This feature allows you to move traffic in both forward and backward directions. This feature allows only one reverse metric TLV per IS-IS Hello message. All routers on a link must support the protocol extensions to achieve the desired results. The feature enables including the metric value in the reverse metric Type Length Value (TLV) and the Traffic Engineering (TE) metric value in the sub-TLV to the existing local link and TE metric values of the receiver.
This feature enables you to set the metric value on one end of a remote link. It advertises the value in various IS-Neighbor TLV types and uses the value when installing the routes using the remote link in the RIB.
IS-IS reverse metric computes the path based on the metric type you choose. There are two types of metrics:
Narrow: You can use 6 bits, the maximum that you can set for an interface is 63.
Wide: You can use 24 bits, the maximum that you can set for an interface is 2^24-1.
Perform the following steps to configure the Reverse Metric feature.
Router(config)# router isis 1
Router(config-isis)# is-type level-2-only
Router(config-isis)# net 47.0000.0000.0002.00
Router(config-isis)# address-family ipv6 unicast
Router(config-isis-af)# metric-style wide
Router(config-isis-af)# segment-routing srv6
Router(config-isis-srv6)# locator Leaf-PE1
Router(config-isis-srv6-loc)# exit
Router(config-isis-srv6)# exit
Router(config-isis)# exit
Router(config-isis)# interface TenGigE0/1/0/16/3
Router(config-isis-if)# override metrics maximum
Router(config-isis-if)# address-family ipv6 unicast
Router(config-isis-af)# exit
Router(config-isis)# exit
Router(config-isis)# interface TenGigE0/2/0/16/1
Router(config-isis-if)# override metrics high
Router(config-isis-if)# address-family ipv6 unicast
Router(config-isis-af)# exit
Router(config-isis)# exit
This section shows the running configuration of the Reverse Metric feature.
router isis 1
is-type level-2-only
net 47.0000.0000.0002.00
address-family ipv6 unicast
metric-style wide
segment-routing srv6
locator Leaf_PE1
!
!
!
interface TenGigE 0/1/0/16/3
override metrics maximum
address-family ipv6 unicast
!
!
interface TenGigE 0/2/0/16/1
override metrics high
address-family ipv6 unicast
!
Verify the Reverse Metric.feature.
Router:Leaf-PE1#show isis database internal ver Leaf-PE1
IS-IS 1 (Level-2) Link State Database
LSPID LSP Seq Num LSP Checksum LSP Holdtime/Rcvd ATT/P/OL LSP Length
Leaf-PE1.00-00 * 0x0000001e 0x71ee 1184 /* 0/0/0 189
TLV code:1 length:2
Area Address: 47
TLV code:129 length:1
NLPID: 0x8e
TLV code:137 length:8
Hostname: Leaf-PE1
TLV code:229 length:2
MT: IPv6 Unicast 0/0/0
TLV code:237 length:50
Metric: 16777215 MT (IPv6 Unicast) IPv6 10:2:4::/112
SubTLV code:4 length:1
Prefix Attribute Flags: X:0 R:0 N:0
Metric: 16777214 MT (IPv6 Unicast) IPv6 10:2:11::/112
SubTLV code:4 length:1
Prefix Attribute Flags: X:0 R:0 N:0
Certain events like process restart or reload can involve a significant processing overhead. Updating routing tables with all adjacencies, maintaining them, and synchronizing the database with each adjacent router requires a lot of bandwidth. These processes may require large number of packets being sent and/or received, depending on the state of the database on the routers. If packets are dropped in any direction, it can lead to an unstable state.
We cannot prevent events like process restart or reload, but we can handle such events better by limiting the number of adjacencies that area being established simultaneously. To limit the number of adjacencies from getting established simultaneously, you can configure adjacency stagger. By configuring IS-IS adjacency stagger, you can specify the initial number neighbourhood routers from which adjacencies can fully form after a process restart or reload. If you configure IS-IS adjacency stagger, you can also specify the subsequent number of simultaneous neighbors that are allowed to form adjacency.
IS-IS adjacency stagger is only supported on point-to-point interfaces and not on LAN interfaces.
IS-IS adjacency stagger is not supported with NSF (non-stop forwarding) mechanisms.
To configure IS-IS adjacency stagger on a point-to-point interface, you must use the following configuration steps:
Configure IS-IS.
Configure adjacency stagger.
/* Enter the global configuration mode and configure IS-IS */
Router# config
Router(config)# router isis 1
/* Configure IS-IS adjacency stagger */
Router(config-isis)# adjacency stagger 2 3
Router(config-isis)# commit|
Feature Name |
Release Information |
Feature Description |
|---|---|---|
|
32 IS-IS Instances |
Release 7.6.1 |
You can now configure up to 32 IS-IS instances, thus enhancing the ability to isolate resources within your router and on the network. This ability enables you to configure more instances consuming network-wide resources at different rates, giving you more flexibility to manage your networks efficiently. In earlier releases, you could configure up to16 IS-IS instances. |
You can configure up to 32 IS-IS instances per router, as long as segment-routing mpls is not configured under router isis . Multiple IS-IS instances can share a single interface if the instances you configure are with different instance IDs.
If segment-routing mpls is configured under router isis , then IS-IS takes the connection to Label Switching Database (LSD) component within the router. Configuring 32 IS-IS instances may exceed the 32 connections that are allowed to LSD. These connections are given out on a first-come-first-serve basis. It is possible for the IS-IS instances to take them all and prevent other clients like LDP, BGP, and so on, from getting connections. This may have adverse effects on the system.
Note |
IS-IS does not connect to LSD unless it needs one due to segment-routing mpls configuration. So, you can configure any number of connections up to 32, as long as the segment-routing mpls is not configured. Ensure caution if SR-MPLS is in use. |
Use the show mpls lsd clients command to determine how many IS-IS instances you can configure. To do this, bring up the system without any IS-IS configuration and observe the number of LSD clients.
RP/0/0/CPU0:r100#show mpls lsd clients
Wed Mar 16 08:10:32.646 PDT
ID Services Location
-- ------------------------------------ ------------
0 LSD(A) 0/0/CPU0
1 Static(A) 0/0/CPU0
2 L2VPN(A) 0/0/CPU0
3 PIM6:pim6(A) 0/0/CPU0
4 Application-Controller:XTC(A) 0/0/CPU0
5 PIM:pim(A) 0/0/CPU0
6 BFD(A) 0/0/CPU0
7 TE-Control(A) 0/0/CPU0
8 LDP(A) 0/0/CPU0In the example, nine client connections are being used, leaving 23 for use by IS-IS instances or other clients.
Because the Routing Information Base (RIB) treats each of the IS-IS instances as equal routing clients, you must be careful when redistributing routes between IS-IS instances. The RIB does not know to prefer Level 1 routes over Level 2 routes. For this reason, if you are running Level 1 and Level 2 instances, you must enforce the preference by configuring different administrative distances for the two instances.
|
Feature Name |
Release Information |
Feature Description |
| MPLS TE Preference for Tunnels |
Release 7.6.1 |
You can now configure the MPLS TE traffic for equal-cost multipath (ECMP) such that it flows only through TE tunnels. This is useful in scenarios where the hardware has resource constraints that limit the number of mixed ECMP routes. In earlier releases, IS-IS installed multiple ECMPs for a route in the Routing Information Base (RIB) through TE tunnels and physical interfaces by default. This feature introduces the following command: |
The MPLS TE feature enables an MPLS backbone to replicate and expand the traffic engineering capabilities of Layer 2 ATM and Frame Relay networks. MPLS is an integration of Layer 2 and Layer 3 technologies.
For IS-IS, MPLS TE automatically establishes and maintains MPLS TE label-switched paths across the backbone by using Resource Reservation Protocol (RSVP). The route that a label-switched path uses is determined by the label-switched paths resource requirements and network resources, such as bandwidth. Available resources are flooded by using special IS-IS TLV extensions in the IS-IS. The label-switched paths are explicit routes and are referred to as traffic engineering (TE) tunnels.
The overload bit is a special bit of state information that is included in an LSP of the router. If the bit is set on the router, it notifies routers in the area that the router is not available for transit traffic. This capability is useful in four situations:
During a serious but nonfatal error, such as limited memory.
During the startup and restart of the process. The overload bit can be set until the routing protocol has converged. However, it is not employed during a normal NSF restart or failover because doing so causes a routing flap.
During a trial deployment of a new router. The overload bit can be set until deployment is verified, then cleared.
During the shutdown of a router. The overload bit can be set to remove the router from the topology before the router is removed from service.
Because the overload bit applies to forwarding for a single topology, it may be configured and cleared independently for IPv4 and IPv6 during multitopology operation. For this reason, the overload is set from the router address family configuration mode. If the IPv4 overload bit is set, all routers in the area do not use the router for IPv4 transit traffic. However, they can still use the router for IPv6 transit traffic.
The IS-IS overload bit avoidance feature allows network administrators to prevent label switched paths (LSPs) from being disabled when a router in that path has its Intermediate System-to-Intermediate System (IS-IS) overload bit set.
When the IS-IS overload bit avoidance feature is activated, all nodes with the overload bit set, including head nodes, mid nodes, and tail nodes, are ignored, which means that they are still available for use with label switched paths (LSPs).
Note |
The IS-IS overload bit avoidance feature does not change the default behavior on nodes that have their overload bit set if those nodes are not included in the path calculation (PCALC). |
The IS-IS overload bit avoidance feature is activated using the following command:
mpls traffic-eng path-selection ignore overload
The IS-IS overload bit avoidance feature is deactivated using the no form of this command:
no mpls traffic-eng path-selection ignore overload
When the IS-IS overload bit avoidance feature is deactivated, nodes with the overload bit set cannot be used as nodes of last resort.
You can force a default route into an IS-IS routing domain. Whenever you specifically configure redistribution of routes into an IS-IS routing domain, the Cisco IOS XR software does not, by default, redistribute the default route into the IS-IS routing domain. The default-information originate command generates a default route into IS-IS, which can be controlled by a route policy. You can use the route policy to identify the level into which the default route is to be announced, and you can specify other filtering options configurable under a route policy. You can use a route policy to conditionally advertise the default route, depending on the existence of another route in the routing table of the router.
The attached bit is set in a router that is configured with the is-type command and level-1-2 keyword. The attached bit indicates that the router is connected to other areas (typically through the backbone). This functionality means that the router can be used by Level 1 routers in the area as the default route to the backbone. The attached bit is usually set automatically as the router discovers other areas while computing its Level 2 SPF route. The bit is automatically cleared when the router becomes detached from the backbone.
Note |
If the connectivity for the Level 2 instance is lost, the attached bit in the Level 1 instance LSP would continue sending traffic to the Level 2 instance and cause the traffic to be dropped. |
To simulate this behavior when using multiple processes to represent the level-1-2 keyword functionality, you would manually configure the attached bit on the Level 1 process.
The IS-IS Support for route tags feature provides the capability to associate and advertise a tag with an IS-IS route prefix. Additionally, the feature allows you to prioritize the order of installation of route prefixes in the RIB based on a tag of a route. Route tags may also be used in route policy to match route prefixes (for example, to select certain route prefixes for redistribution).
The multicast-intact feature provides the ability to run multicast routing (PIM) when IGP shortcuts are configured and active on the router. Both OSPFv2 and IS-IS support the multicast-intact feature. MPLS TE and IP multicast coexistence is supported in Cisco IOS XR software by using the mpls traffic-eng multicast-intact IS-IS or OSPF router command.
You can enable multicast-intact in the IGP when multicast routing protocols (PIM) are configured and IGP shortcuts are configured on the router. IGP shortcuts are MPLS tunnels that are exposed to IGP. The IGPs route the IP traffic over these tunnels to destinations that are downstream from the egress router of the tunnel (from an SPF perspective). PIM cannot use IGP shortcuts for propagating PIM joins because reverse path forwarding (RPF) cannot work across a unidirectional tunnel.
When you enable multicast-intact on an IGP, the IGP publishes a parallel or alternate set of equal-cost next-hops for use by PIM. These next-hops are called mcast-intact next-hops. The mcast-intact next-hops have the following attributes:
They are guaranteed not to contain any IGP shortcuts.
They are not used for unicast routing but are used only by PIM to look up an IPv4 next-hop to a PIM source.
They are not published to the FIB.
When multicast-intact is enabled on an IGP, all IPv4 destinations that were learned through link-state advertisements are published with a set equal-cost mcast-intact next-hops to the RIB. This attribute applies even when the native next-hops have no IGP shortcuts.
In IS-IS, the max-paths limit is applied by counting both the native and mcast-intact next-hops together. (In OSPFv2, the behavior is slightly different.)
Multicast topology support allows for the configuration of IS-IS multicast topologies for IPv4 or IPv6 routing. IS-IS maintains a separate topology for multicast and runs a separate Shortest Path First (SPF) over the multicast topology. IS-IS multicast inserts routes from the IS-IS multicast topology into the multicast-unicast Routing Information Base (muRIB) table in the RIB for the corresponding address family. Since PIM uses the muRIB, PIM uses routes from the multicast topology instead of routes from the unicast topology.
Multiprotocol Label Switching (MPLS) Label Distribution Protocol (LDP) Interior Gateway Protocol (IGP) Synchronization ensures that LDP has completed label exchange before the IGP path is used for switching. MPLS traffic loss can occur in the following two situations:
When an IGP adjacency is established, the router begins forwarding packets using the new adjacency before LDP has exchanged labels with peers on that link.
When an LDP session closes, the router continues to forward traffic using the link associated with the LDP peer rather than using an alternate path with an established LDP session.
This feature provides a mechanism to synchronize LDP and IS-IS to minimize MPLS packet loss. The synchronization is accomplished by changing the link metric for a neighbor IS-IS link-state packet (LSP), based on the state of the LDP session.
When an IS-IS adjacency is established on a link but the LDP session is lost or LDP has not yet completed exchanging labels, IS-IS advertises the maximum metric on that link. In this instance, LDP IS-IS synchronization is not yet achieved.
Note |
In IS-IS, a link with a maximum wide metric (0xFFFFFF) is not considered for shortest path first (SPF). Therefore, the maximum wide metric of -1 (0XFFFFFE) is used with MPLS LDP IGP synchronization. |
When LDP IS-IS synchronization is achieved, IS-IS advertises a regular (configured or default) metric on that link.
LDP graceful restart protects traffic when an LDP session is lost. If a graceful restart-enabled LDP session fails, MPLS LDP IS-IS synchronization is still achieved on the interface while it is protected by graceful restart. MPLS LDP IGP synchronization is eventually lost under the following circumstances:
LDP fails to restart before the LDP graceful restart reconnect timer expires.
The LDP session on the protected interface fails to recover before the LDP graceful restart recovery timer expires.
IS-IS nonstop forwarding (NSF) protects traffic during IS-IS process restarts and route processor (RP) failovers. LDP IS-IS synchronization is supported with IS-IS NSF only if LDP graceful restart is also enabled over the interface. If IS-IS NSF is not enabled, the LDP synchronization state is not retained across restarts and failovers.
Label Distribution Protocol (LDP) Interior Gateway Protocol (IGP) auto-configuration simplifies the procedure to enable LDP on a set of interfaces used by an IGP instance. LDP IGP auto-configuration can be used on a large number interfaces (for example, when LDP is used for transport in the core) and on multiple IGP instances simultaneously.
This feature supports the IPv4 address family for the default VPN routing and forwarding (VRF) instance.
LDP IGP auto-configuration can also be explicitly disabled on individual interfaces under LDP using the igp auto-config disable command. This allows LDP to receive all IGP interfaces except the ones explicitly disabled.
See the MPLS configuration guide for information on configuring LDP IGP auto-configuration.
MPLS TE forwarding adjacency allows a network administrator to handle a traffic engineering, label switch path (LSP) tunnel as a link in an Interior Gateway Protocol (IGP) network, based on the Shortest Path First (SPF) algorithm. A forwarding adjacency can be created between routers in the same IS-IS level. The routers can be located multiple hops from each other. As a result, a TE tunnel is advertised as a link in an IGP network, with the cost of the link associated with it. Routers outside of the TE domain see the TE tunnel and use it to compute the shortest path for routing traffic throughout the network.
MPLS TE forwarding adjacency is considered in IS-IS SPF only if a two-way connectivity check is achieved. This is possible if the forwarding adjacency is bidirectional or the head end and tail end routers of the MPLS TE tunnel are adjacent.
The MPLS TE forwarding adjacency feature is supported by IS-IS. For details on configuring MPLS TE forwarding adjacency, see the MPLS Configuration Guide.
MPLS TE interarea tunnels allow you to establish MPLS TE tunnels that span multiple IGP areas (Open Shorted Path First [OSPF]) and levels (IS-IS), removing the restriction that required that both the tunnel headend and tailend routers be in the same area. The IGP can be either IS-IS or OSPF. See the Configuring MPLS Traffic Engineering for IS-IS for information on configuring MPLS TE for IS-IS.
For details on configuring MPLS TE interarea tunnels, see the MPLS Configuration Guide.
The IP Fast Reroute (IPFRR) loop-free alternate (LFA) computation provides protection against link failure. Locally computed repair paths are used to prevent packet loss caused by loops that occur during network reconvergence after a failure. See IETF draft-ietf-rtgwg-ipfrr-framework-06.txt and draft-ietf-rtgwg-lf-conv-frmwk-00.txt for detailed information on IPFRR LFA.
IPFRR LFA is different from Multiprotocol Label Switching (MPLS) as it is applicable to networks using conventional IP routing and forwarding. See MPLS Configuration Guide for Cisco ASR 9000 Series Routers for information on configuring MPLS IPFRR.
The unequal cost multipath (UCMP) load-balancing adds the capability with intermediate system-to-intermediate system (IS-IS) to load-balance traffic proportionally across multiple paths, with different cost.
Generally, higher bandwidth paths have lower IGP metrics configured, so that they form the shortest IGP paths. With the UCMP load-balancing enabled, IGP can use even lower bandwidth paths or higher cost paths for traffic, and can install these paths to the forwarding information base (FIB). IS-IS IGP still installs multiple paths to the same destination in FIB, but each path will have a 'load metric/weight' associated with it. FIB uses this load metric/weight to decide the amount of traffic that needs to be sent on a higher bandwidth path and the amount of traffic that needs to be sent on a lower bandwidth path.
The UCMP computation is provided under IS-IS per address family, enabling UCMP computation for a particular address family. The UCMP configuration is also provided with a prefix-list option, which would limit the UCMP computation only for the prefixes present in the prefix-list. If prefix-list option is not provided, UCMP computation is done for the reachable prefixes in IS-IS. The number of UCMP nexthops to be considered and installed is controlled using the variance configuration. Variance value identifies the range for the UCMP path metric to be considered for installation into routing information base (RIB) and is defined in terms of a percentage of the primary path metric. Total number of paths, including ECMP and UCMP paths together is limited by the max-path configuration or by the max-path capability of the platform.
Enabling the UCMP configuration indicates that IS-IS should perform UCMP computation for the all the reachable ISIS prefixes or all the prefixes in the prefix-list, if the prefix-list option is used. The UCMP computation happens only after the primary SPF and route calculation is completed. There would be a delay of ISIS_UCMP_INITIAL_DELAY (default delay is 100 ms) milliseconds from the time route calculation is completed and UCMP computation is started. UCMP computation will be done before fast re-route computation. Fast re-route backup paths will be calculated for both the primary equal cost multipath ( ECMP) paths and the UCMP paths. Use the ucmp delay-interval command to configure the delay between primary SPF completion and start of UCMP computation.
To manually change each path's bandwidth to adjust UCMP ratio, use the bandwidth command in interface configuration mode.
UCMP ratio can be adjusted by any of the following ways:
By using the bandwidth command in interface configuration mode to manually change the UCMP ratio.
By adjusting the ISIS metric on the links.
There is an option to exclude an interface from being used for UCMP computation. If it is desired that a particular interface should not be considered as a UCMP nexthop, for any prefix, then use the ucmp exclude interface command to configure the interface to be excluded from UCMP computation.
More than 32 ECMP and UCMP paths are not supported for these features:
LI
GRE
BVI
NetFlow
Satellite
MCAST
SPAN
PWHE
ABF
P2MP
MVPN
VPLS
L2TPv3
LISP
VIDMON
PBR
During a route processor failover (RPFO), IS-IS does not maintain maximum paths for a certain minimum amount of time. During this time, there is a minor amount of traffic flowing through a certain number of paths beyond the configured number of maximum paths.
To avoid such a scenario in Cisco access points, the interfaces are configured to have a maximum number of maximum paths so that traffic is forced to choose one among the configured ECMP maximum paths only.
This task explains how to enable IS-IS and configure the routing level for an area.
Note |
Configuring the routing level in Step 4 is optional, but is highly recommended to establish the proper level of adjacencies. |
Although you can configure IS-IS before you configure an IP address, no IS-IS routing occurs until at least one IP address is configured.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
router isis instance-id Example: |
Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.
|
|
Step 3 |
net network-entity-title Example: |
Configures network entity titles (NETs) for the routing instance.
|
|
Step 4 |
is-type { level-1 | level-1-2 | level-2-only } Example: |
(Optional) Configures the system type (area or backbone router).
|
|
Step 5 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
|
Step 6 |
show isis [ instance instance-id ] protocol Example: |
(Optional) Displays summary information about the IS-IS instance. |
After an IS-IS instance is enabled, it must be configured to compute routes for a specific network topology.
This task explains how to configure the operation of the IS-IS protocol on an interface for an IPv4 or IPv6 topology.
Note |
To enable the router to run in single-topology mode, configure each of the IS-IS interfaces with all of the address families enabled and “single-topology” in the address-family IPv6 unicast in the IS-IS router stanza. You can use either the IPv6 address family or both IPv4 and IPv6 address families, but your configuration must represent the set of all active address families on the router. Additionally, explicitly enable single-topology operation by configuring it in the IPv6 router address family submode. Two exceptions to these instructions exist:
The default metric style for single topology is narrow metrics. However, you can use either wide metrics or narrow metrics. How to configure them depends on how single topology is configured. If both IPv4 and IPv6 are enabled and single topology is configured, the metric style is configured in the address-family ipv4 stanza. You may configure the metric style in the address-family ipv6 stanza, but it is ignored in this case. If only IPv6 is enabled and single topology is configured, then the metric style is configured in the address-family ipv6 stanza. |
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
interface type interface-path-id Example: |
Enters interface configuration mode. |
|
Step 3 |
Do one of the following:
Example:or |
Defines the IPv4 address for the interface. An IP address is required on all interfaces in an area enabled for IS-IS if any one interface is configured for IS-IS routing. or Specifies an IPv6 network assigned to the interface and enables IPv6 processing on the interface with the eui-64 keyword. or Specifies an IPv6 address assigned to the interface and enables IPv6 processing on the interface with the link-local keyword. or Automatically configures an IPv6 link-local address on the interface while also enabling the interface for IPv6 processing.
|
|
Step 4 |
exit Example: |
Exits interface configuration mode, and returns the router to global configuration mode. |
|
Step 5 |
router isis instance-id Example: |
Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.
|
|
Step 6 |
net network-entity-title Example: |
Configures NETs for the routing instance.
|
|
Step 7 |
address-family ipv6 [ unicast ] Example: |
Specifies the IPv6 address family and enters router address family configuration mode.
|
|
Step 8 |
single-topology Example: |
(Optional) Configures the link topology for IPv4 when IPv6 is configured.
|
|
Step 9 |
exit Example: |
Exits router address family configuration mode, and returns the router to router configuration mode. |
|
Step 10 |
interface type interface-path-id Example: |
Enters interface configuration mode. |
|
Step 11 |
circuit-type { level-1 | level-1-2 | level-2-only } Example: |
(Optional) Configures the type of adjacency.
|
|
Step 12 |
address-family { ipv4 | ipv6 } [ unicast | multicast ] Example: |
Specifies the IPv4 or IPv6 address family, and enters interface address family configuration mode.
|
|
Step 13 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
|
Step 14 |
show isis [ instance instance-id ] interface [ type interface-path-id ] [ detail ] [ level { 1 | 2 }] Example: |
(Optional) Displays information about the IS-IS interface. |
|
Step 15 |
show isis [ instance instance-id ] topology [ systemid system-id ] [ level { 1 | 2 }] [ summary ] Example: |
(Optional) Displays a list of connected routers in all areas. |
This set of procedures configures multitopology routing, which is used by PIM for reverse-path forwarding (RPF) path selection.
Only the default VRF is currently supported in a multitopology solution.
Only protocol-independent multicast (PIM) and intermediate system-intermediate system (IS-IS) routing protocols are currently supported.
Topology selection is restricted solely to (S, G) route sources for both SM and SSM. Static and IS-IS are the only interior gateway protocols (IGPs) that support multitopology deployment.
For non-(S, G) route sources like a rendezvous point or bootstrap router (BSR), or when a route policy is not configured, the current policy default remains in effect. In other words, either a unicast-default or multicast-default table is selected for all sources, based on OSFP/IS-IS/Multiprotocol Border Gateway Protocol (MBGP) configuration.
Note |
Although both multicast and unicast keywords are available when using the address-family {ipv4 | ipv6} command in routing policy language (RPL), only topologies under multicast SAFI can be configured globally. |
Configuring multitopology networks requires the following tasks:
Follow these steps to enable a global topology in the default VRF and to enable its use with a specific interface.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
address-family { ipv4 | ipv6 } multicast topology topo-name Example: |
Configures a topology in the default VRF table that will be associated with a an interface. |
|
Step 3 |
maximum prefix limit Example: |
(Optional) Limits the number of prefixes allowed in a topology routing table. Range is 32 to 2000000. |
|
Step 4 |
interface type interface-path-id Example: |
Specifies the interface to be associated with the previously specified VRF table that will add the connected and local routes to the appropriate routing table. |
|
Step 5 |
address-family { ipv4 | ipv6 } multicast topology topo-name Example: |
Enables the topology for the interface specified in Step 4, adding the connected and local routes to the appropriate routing table. |
|
Step 6 |
Repeat Step 4 and Step 5 until you have specified all the interface instances you want to associate with your topologies. Example: |
|
|
Step 7 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
To enable a topology in IS-IS, you must associate an IS-IS topology ID with the named topology. IS-IS uses the topology ID to differentiate topologies in the domain.
Note |
This command must be configured prior to other topology commands. |
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
router isis instance-id Example: |
Enters IS-IS configuration submode. |
|
Step 3 |
address-family { ipv4 | ipv6 } multicast topology topo-name Example: |
Associates an IS-IS topology ID with the named topology. |
|
Step 4 |
topology-id multitoplogy-id Example: |
Configures the numeric multitopologyID in IS-IS that identifies the topology. Range is 6 to 4095. |
|
Step 5 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
To associate an interface with a topology in IS-IS, follow these steps.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
router isis instance-id Example: |
Enters IS-IS configuration submode. |
|
Step 3 |
net network-entity-title Example: |
Creates a network entity title for the configured isis interface. |
|
Step 4 |
interface type interface-path-id Example: |
Enters isis interface configuration submode and creates an interface instance. |
|
Step 5 |
address-family { ipv4 | ipv6 } multicast topology topo-name Example: |
|
|
Step 6 |
Repeat Step 4 and Step 5 until you have specified all the interface instances and associated topologies you want to configure in your network. |
|
|
Step 7 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
For more information about creating a routing policy and about the set rpf-topology command, see Routing Command Reference for Cisco ASR 9000 Series Routers.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
route-policy policy-name Example: |
Defines a routing policy and enters routing policy configuration submode. For detailed information about the use of the set-rpf-topology and other routing configuration commands, see Routing Command Reference for Cisco ASR 9000 Series Routers. |
|
Step 3 |
end-policy Example: |
Signifies the end of route policy definition and exits routing policy configuration submode. |
|
Step 4 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
Multitopology is configured in the same way as the single topology. However, the single - topology command is omitted, invoking the default multitopology behavior. This task is optional.
Flooding of LSPs can limit network scalability. You can control LSP flooding by tuning your LSP database parameters on the router globally or on the interface. This task is optional.
Many of the commands to control LSP flooding contain an option to specify the level to which they apply. Without the option, the command applies to both levels. If an option is configured for one level, the other level continues to use the default value. To configure options for both levels, use the command twice. For example:
RP/0/RSP0/CPU0:router(config-isis)# lsp-refresh-interval 1200 level 2
RP/0/RSP0/CPU0:router(config-isis)# lsp-refresh-interval 1100 level 1
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
router isis instance-id Example: |
Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.
|
|
Step 3 |
lsp-refresh-interval seconds [ level { 1 | 2 }] Example: |
(Optional) Sets the time between regeneration of LSPs that contain different sequence numbers
|
|
Step 4 |
lsp-check-interval seconds [ level { 1 | 2 }] Example: |
(Optional) Configures the time between periodic checks of the entire database to validate the checksums of the LSPs in the database.
|
|
Step 5 |
lsp-gen-interval { [ initial-wait initial | secondary-wait secondary | maximum-wait maximum ] ... } [ level { 1 | 2 }] Example: |
(Optional) Reduces the rate of LSP generation during periods of instability in the network. Helps reduce the CPU load on the router and number of LSP transmissions to its IS-IS neighbors.
|
|
Step 6 |
lsp-mtu bytes [ level { 1 | 2 }] Example: |
(Optional) Sets the maximum transmission unit (MTU) size of LSPs. |
|
Step 7 |
max-lsp-lifetime seconds [ level { 1 | 2 }] Example: |
(Optional) Sets the initial lifetime given to an LSP originated by the router.
|
|
Step 8 |
ignore-lsp-errors disable Example: |
(Optional) Sets the router to purge LSPs received with checksum errors. |
|
Step 9 |
interface type interface-path-id Example: |
Enters interface configuration mode. |
|
Step 10 |
lsp-interval milliseconds [ level { 1 | 2 }] Example: |
(Optional) Configures the amount of time between each LSP sent on an interface. |
|
Step 11 |
csnp-interval seconds [ level { 1 | 2 }] Example: |
(Optional) Configures the interval at which periodic CSNP packets are sent on broadcast interfaces.
|
|
Step 12 |
retransmit-interval seconds [ level { 1 | 2 }] Example: |
(Optional) Configures the amount of time that the sending router waits for an acknowledgment before it considers that the LSP was not received and subsequently resends. |
|
Step 13 |
retransmit-throttle-interval milliseconds [ level { 1 | 2 }] Example: |
(Optional) Configures the amount of time between retransmissions on each LSP on a point-to-point interface.
|
|
Step 14 |
mesh-group { number | blocked } Example: |
(Optional) Optimizes LSP flooding in NBMA networks with highly meshed, point-to-point topologies.
|
|
Step 15 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
|
Step 16 |
show isis interface [ type interface-path-id | level { 1 | 2 }] [ brief ] Example: |
(Optional) Displays information about the IS-IS interface. |
|
Step 17 |
show isis [ instance instance-id ] database [ level { 1 | 2 }] [ detail | summary | verbose ] [ * | lsp-id ] Example: |
(Optional) Displays the IS-IS LSP database. |
|
Step 18 |
show isis [ instance instance-id ] lsp-log [ level { 1 | 2 }] Example: |
(Optional) Displays LSP log information. |
|
Step 19 |
show isis database-log [ level { 1 | 2 }] Example: |
(Optional) Display IS-IS database log information. |
This task explains how to configure your router with NSF that allows the Cisco IOS XR software to resynchronize the IS-IS link-state database with its IS-IS neighbors after a process restart. The process restart could be due to an:
RP failover (for a warm restart)
Simple process restart (due to an IS-IS reload or other administrative request to restart the process)
IS-IS software upgrade
In all cases, NSF mitigates link flaps and loss of user sessions. This task is optional.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
router isis instance-id Example: |
Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.
|
|
Step 3 |
nsf { cisco | ietf } Example: |
Enables NSF on the next restart.
|
|
Step 4 |
nsf interface-expires number Example: |
Configures the number of resends of an acknowledged NSF-restart acknowledgment.
|
|
Step 5 |
nsf interface-timer seconds Example: |
Configures the number of seconds to wait for each restart acknowledgment. |
|
Step 6 |
nsf lifetime seconds Example: |
Configures the maximum route lifetime following an NSF restart.
|
|
Step 7 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
|
Step 8 |
show running-config [ command ] Example: |
(Optional) Displays the entire contents of the currently running configuration file or a subset of that file.
|
|
Step 1 |
configure Example:Enters global configuration mode. |
|
Step 2 |
router isis instance-id Example:Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode. |
|
Step 3 |
nsr Example:Configures the NSR feature. |
|
Step 4 |
Use the commit or end command. commit —Saves the configuration changes and remains within the configuration session.
|
|
Step 5 |
show isis nsr adjacency Example:Displays adjacency information. |
|
Step 6 |
show isis nsr status Example:Displays the NSR status information. |
|
Step 7 |
show isis nsr statistics Example:Shows number of ISIS adjacencies, lsps, routes, tunnels, Te links on active and standby routers. |
This task explains how to configure authentication for IS-IS. This task is optional.
| Command or Action | Purpose | |||
|---|---|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
||
|
Step 2 |
router isis instance-id Example: |
Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.
|
||
|
Step 3 |
lsp-password { hmac-md5 | text } { clear | encrypted } password [ level { 1 | 2 }] [ send-only ] [ snp send-only ] | [enable-poi] ] Example: |
Configures the LSP authentication password.
|
||
|
Step 4 |
interface type interface-path-id Example: |
Enters interface configuration mode. |
||
|
Step 5 |
hello-password { hmac-md5 | text } { clear | encrypted } password [ level { 1 | 2 }] [ send-only ] Example: |
Configures the authentication password for an IS-IS interface. |
||
|
Step 6 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
This task explains how to configure keychains for IS-IS. This task is optional.
Keychains can be configured at the router level ( lsp-password command) and at the interface level ( hello-password command) within IS-IS. These commands reference the global keychain configuration and instruct the IS-IS protocol to obtain security parameters from the global set of configured keychains. The router-level configuration (lsp-password command) sets the keychain to be used for all IS-IS LSPs generated by this router, as well as for all Sequence Number Protocol Data Units (SN PDUs). The keychain used for HELLO PDUs is set at the interface level, and may be set differently for each interface configured for IS-IS.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
router isis instance-id Example: |
Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.
|
|
Step 3 |
l sp-password keychain keychain-name [ level { 1 | 2 }] [ send-only ] [ snp send-only ] Example: |
Configures the keychain. |
|
Step 4 |
interface type interface-path-id Example: |
Enters interface configuration mode. |
|
Step 5 |
h ello-password keychain keychain-name [ level { 1 | 2 }] [ send-only ] Example: |
Configures the authentication password for an IS-IS interface. |
|
Step 6 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
This task explains how to configure IS-IS for MPLS TE. This task is optional.
For a description of the MPLS TE tasks and commands that allow you to configure the router to support tunnels, configure an MPLS tunnel that IS-IS can use, and troubleshoot MPLS TE, see Implementing MPLS Traffic Engineering on MPLS Configuration Guide for Cisco ASR 9000 Series Routers
Your network must support the MPLS Cisco IOS XR software feature before you enable MPLS TE for IS-IS on your router.
Note |
You must enter the commands in the following task list on every IS-IS router in the traffic-engineered portion of your network. |
Note |
MPLS traffic engineering currently does not support routing and signaling of LSPs over unnumbered IP links. Therefore, do not configure the feature over those links. |
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
router isis instance-id Example: |
Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.
|
|
Step 3 |
address-family { ipv4 | ipv6 } [ unicast ] Example: |
Specifies the IPv4 or IPv6 address family, and enters router address family configuration mode. |
|
Step 4 |
mpls traffic-eng level { 1 | 2 } Example: |
Configures a router running IS-IS to flood MPLS TE link information into the indicated IS-IS level. |
|
Step 5 |
mpls traffic-eng router-id { ip-address | interface-name interface-instance } Example: |
Specifies that the MPLS TE router identifier for the node is the given IP address or an IP address associated with the given interface. |
|
Step 6 |
mpls traffic-eng tunnel preferred Example: |
This is an optional command to prevent IS-IS from installing routes that use both MPLS-TE tunnels and physical interfaces. |
|
Step 7 |
metric-style wide [ level { 1 | 2 }] Example: |
Configures a router to generate and accept only wide link metrics in the Level 1 area. |
|
Step 8 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
|
Step 9 |
show isis [ instance instance-id ] mpls traffic-eng tunnel Example: |
(Optional) Displays MPLS TE tunnel information. |
|
Step 10 |
show isis [ instance instance-id ] mpls traffic-eng adjacency-log Example: |
(Optional) Displays a log of MPLS TE IS-IS adjacency changes. |
|
Step 11 |
show isis [ instance instance-id ] mpls traffic-eng advertisements Example: |
(Optional) Displays the latest flooded record from MPLS TE. |
This task explains how to enable logging of adjacency state changes, alter the timers for IS-IS adjacency packets, and display various aspects of adjacency state. Tuning your IS-IS adjacencies increases network stability when links are congested. This task is optional.
For point-to-point links, IS-IS sends only a single hello for Level 1 and Level 2, which means that the level modifiers are meaningless on point-to-point links. To modify hello parameters for a point-to-point interface, omit the specification of the level options.
The options configurable in the interface submode apply only to that interface. By default, the values are applied to both Level 1 and Level 2.
The hello-password command can be used to prevent adjacency formation with unauthorized or undesired routers. This ability is particularly useful on a LAN, where connections to routers with which you have no desire to establish adjacencies are commonly found.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
router isis instance-id Example: |
Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.
|
|
Step 3 |
log adjacency changes Example: |
Generates a log message when an IS-IS adjacency changes state (up or down). |
|
Step 4 |
interface type interface-path-id Example: |
Enters interface configuration mode. |
|
Step 5 |
hello-padding { disable | sometimes } [ level { 1 | 2 }] Example: |
Configures padding on IS-IS hello PDUs for an IS-IS interface on the router.
|
|
Step 6 |
hello-interval seconds [ level { 1 | 2 }] Example: |
Specifies the length of time between hello packets that the software sends. |
|
Step 7 |
hello-multiplier multiplier [ level { 1 | 2 }] Example: |
Specifies the number of IS-IS hello packets a neighbor must miss before the router should declare the adjacency as down.
|
|
Step 8 |
h ello-password { hmac-md5 | text } { clear | encrypted } password [ level { 1 | 2 }] [ send-only ] Example: |
Specifies that this system include authentication in the hello packets and requires successful authentication of the hello packet from the neighbor to establish an adjacency. |
|
Step 9 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
|
Step 10 |
show isis [ instance instance-id ] adjacency t ype interface- path-id ] [ detail ] [ systemid system-id ] Example: |
(Optional) Displays IS-IS adjacencies. |
|
Step 11 |
show isis adjacency-log Example: |
(Optional) Displays a log of the most recent adjacency state transitions. |
|
Step 12 |
show isis [ instance instance-id ] interface [ type interface-path-id ] [ brief | detail ] [ level { 1 | 2 }] Example: |
(Optional) Displays information about the IS-IS interface. |
|
Step 13 |
show isis [ instance instance-id ] neighbors [ interface-type interface-instance ] [ summary ] [ detail ] [ systemid system-id ] Example: |
(Optional) Displays information about IS-IS neighbors. |
This task explains how to make adjustments to the SPF calculation to tune router performance. This task is optional.
Because the SPF calculation computes routes for a particular topology, the tuning attributes are located in the router address family configuration submode. SPF calculation computes routes for Level 1 and Level 2 separately.
When IPv4 and IPv6 address families are used in a single-topology mode, only a single SPF for the IPv4 topology exists. The IPv6 topology “borrows” the IPv4 topology; therefore, no SPF calculation is required for IPv6. To tune the SPF calculation parameters for single-topology mode, configure the address-family ipv4 unicast command.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
router isis instance-id Example: |
Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.
|
|
Step 3 |
address-family { ipv4 | ipv6 } [ unicast ] Example: |
Specifies the IPv4or IPv6 address family, and enters router address family configuration mode. |
|
Step 4 |
spf-interval {[ initial-wait initial | secondary-wait secondary | maximum-wait maximum ] ...} [ level { 1 | 2 }] Example: |
(Optional) Controls the minimum time between successive SPF calculations.
|
|
Step 5 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
|
Step 6 |
show isis [ instance instance-id ] [[ ipv4 | ipv6 | afi-all ] [ unicast | safi-all ]] spf-log [ level { 1 | 2 }] [ fspf | prc | nhc ] [ detail | verbose ] [ last number | first number ] Example: |
(Optional) Displays how often and why the router has run a full SPF calculation. |
This task explains how to perform route functions that include injecting default routes into your IS-IS routing domain and redistributing routes learned in another IS-IS instance. This task is optional.
| Command or Action | Purpose | |||||
|---|---|---|---|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
||||
|
Step 2 |
router isis instance-id Example: |
Enables IS-IS routing for the specified routing process, and places the router in router configuration mode.
|
||||
|
Step 3 |
set-overload-bit [ on-startup { delay | wait-for-bgp }] [ level { 1 | 2 }] Example: |
(Optional) Sets the overload bit.
|
||||
|
Step 4 |
address-family { ipv4 | ipv6 } [ unicast ] Example: |
Specifies the IPv4 or IPv6 address family, and enters router address family configuration mode. |
||||
|
Step 5 |
default-information originate [ route-policy route-policy-name ] Example: |
(Optional) Injects a default IPv4 or IPv6 route into an IS-IS routing domain.
|
||||
|
Step 6 |
distribute-list { { prefix-list prefix-list-name | route-policy route-policy-name} } in Example: |
|
||||
|
Step 7 |
redistribute isis instance [ level-1 | level-2 | level-1-2 ] [ metric metric ] [ metric-type { internal | external }] [ policy policy-name ] Example: |
(Optional) Redistributes routes from one IS-IS instance into another instance.
|
||||
|
Step 8 |
Do one of the following:
Example:or |
(Optional) Allows a Level 1-2 router to summarize Level 1 IPv4 and IPv6 prefixes at Level 2, instead of advertising the Level 1 prefixes directly when the router advertises the summary.
or
|
||||
|
Step 9 |
maximum-paths route-number Example: |
(Optional) Configures the maximum number of parallel paths allowed in a routing table. |
||||
|
Step 10 |
distance weight [ address / prefix-length [ route-list-name ]] Example: |
(Optional) Defines the administrative distance assigned to routes discovered by the IS-IS protocol.
|
||||
|
Step 11 |
set-attached-bit Example: |
(Optional) Configures an IS-IS instance with an attached bit in the Level 1 LSP. |
||||
|
Step 12 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
|
Feature Name |
Release |
Description |
|---|---|---|
|
Maximum Paths Per Algorithm |
Release 7.8.1 |
This feature introduces the new algorithm 0 command. These updates enable individual granularity for regular SPF algorithms. |
A new algorithm 0 command is introduced.
The algorithm 0 command includes the address-family <ipv4/ipv6> unicast subcommand, and a new maximum-paths <maximum-paths> subcommand. The maximum-paths under algorithm 0 configuration block applies to the standard Shortest Path First algorithm of the IS-IS instance.
Note |
For information on IS-IS Flex Algo Maximum Paths, refer to the "Enabling Segment Routing Flexible Algorithm" chapter in the Segment Routing Configuration Guide for Cisco ASR 9000 Series Routers. |
The new subcommands allow for maximum number of Equal-Cost Multi-path (ECMP) to be set for individual algorithms. The value that is configured on a per-algo per address-family basis overrides any value that is configured under the IS-IS global address-family submode.
The maximum-paths per algorithm takes precedence over maximum-paths per address-family.
The maximum paths effective for each SPF algorithm are as follows:
For algorithm 0/Standard SPF:
IPv4: 1
IPv6: 2
Router(config)# router isis isp
Router(config-isis)# address-family ipv4 unicast
Router(config-isis-af)# maximum-paths 12
Router(config-isis-af)# exit
Router(config-isis)# address-family ipv6 unicast
Router(config-isis-af)# maximum-paths 8
Router(config-isis-af)# exit
Router(config-isis)# algorithm 0
Router(config-isis-std-algo)# address-family ipv4 unicast
Router(config-isis-std-algo-af)# maximum-paths 1
Router(config-isis-std-algo)# exit
Router(config-isis-std-algo)# address-family ipv6 unicast
Router(config-isis-std-algo-af)# maximum-paths 2
Router(config-isis-std-algo-af)# exit
|
Feature Name |
Release |
Description |
|---|---|---|
|
Maximum Paths Per Flexible Algorithm Per Prefix |
Release 7.11.1 |
Previously, you could configure a maximum number of Equal-Cost Multi-path (ECMP) to be set for SPF algo 0. This feature provides additional granularity to the IS-IS Maximum Paths Per-Algorithm feature by allowing you to specify a set of prefixes for SPF algo 0. Now you can achieve a balance between path diversity and computational and memory requirements by controlling the number of paths for each specific algorithm and destination prefix combination. This feature introduces these changes: CLI
YANG Data Models:
|
Previously, you could set the maximum paths for a Shortest Path First (SPF) algorithm per address-family.
With this feature, you can further refine the maximum paths configuration by associating it with specific prefixes for each algorithm. The existing maximum-paths command is extended to include a route-policy qualifier to configure the maximum paths per algorithm per prefix-list.
When installing paths into the Routing Information Base (RIB), the system will check if a maximum paths value has been configured for algorithm 0 and the associated prefix. If such a configuration exists, it will be used instead of the existing address-family value to determine the number of paths to be installed.
Note |
Route policies that have the attribute set maximum-paths number are supported. |
Note |
For information on IS-IS Flex Algo Maximum Paths per Prefix, refer to the "Enabling Segment Routing Flexible Algorithm" chapter in the Segment Routing Configuration Guide for Cisco ASR 9000 Series Routers. |
The commands maximum-paths maximum-paths and maximum-paths route-policy rpl-name are mutually exclusive. You can configure either an unqualified number or a route-policy for any given IS-IS instance.
The maximum-paths per algorithm per prefix takes precedence over maximum-paths per algorithm. Likewise, the maximum-paths per algorithm takes precedence over maximum-paths per address-family. This hierarchy ensures that the most specific configuration is prioritized when determining the maximum paths for a given algorithm and prefix combination.
Define a Prefix Set:
prefix-set isis-ipv4-L1
20.1.0.101/32
end-set
Create a Route Policy:
route-policy isis-mp-if-L1
if destination in isis-ipv4-L1 then
set maximum-paths 2
endif
end-policy
Configure Maximum Paths Per-Prefix:
router isis isp
algorithm 0
address-family ipv4 unicast
maximum-paths route-policy isis-mp-if-L1
!
This task explains how to enable Multiprotocol Label Switching (MPLS) Label Distribution Protocol (LDP) IS-IS synchronization. MPLS LDP synchronization can be enabled for an address family under interface configuration mode. Only IPv4 unicast address family is supported. This task is optional.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
router isis instance-id Example: |
Enables IS-IS routing for the specified routing process, and places the router in router configuration mode.
|
|
Step 3 |
interface type interface-path-id Example: |
Enters interface configuration mode. |
|
Step 4 |
address-family ipv4 unicast Example: |
Specifies the IPv4 address family and enters router address family configuration mode. |
|
Step 5 |
mpls ldp sync [ level { 1 | 2 }] Example: |
Enables MPLS LDP synchronization for the IPv4 address family under interface GigabitEthernet 0/1/0/3. |
|
Step 6 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
This optional task describes how to enable multicast-intact for IS-IS routes that use IPv4 and IPv6 addresses.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
router isis instance-id Example: |
Enables IS-IS routing for the specified routing process, and places the router in router configuration mode. In this example, the IS-IS instance is called isp. |
|
Step 3 |
address-family { ipv4 | ipv6 } [ unicast | multicast ] Example: |
Specifies the IPv4 or IPv6 address family, and enters router address family configuration mode. |
|
Step 4 |
mpls traffic-eng multicast-intact Example: |
Enables multicast-intact. |
|
Step 5 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
This optional task describes how to associate a tag with a connected route of an IS-IS interface.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
router isis instance-id Example: |
Enables IS-IS routing for the specified routing process, and places the router in router configuration mode. In this example, the IS-IS instance is called isp. |
|
Step 3 |
address-family { ipv4 | ipv6 } [ unicast ] Example: |
Specifies the IPv4 or IPv6 address family, and enters router address family configuration mode. |
|
Step 4 |
metric-style wide [ transition ] [ level { 1 | 2 }] Example: |
Configures a router to generate and accept only wide link metrics in the Level 1 area. |
|
Step 5 |
exit Example: |
Exits router address family configuration mode, and returns the router to router configuration mode. |
|
Step 6 |
interface type number Example: |
Enters interface configuration mode. |
|
Step 7 |
address-family { ipv4 | ipv6 } [ unicast ] Example: |
Specifies the IPv4 or IPv6 address family, and enters address family configuration mode. |
|
Step 8 |
tag tag Example: |
Sets the value of the tag to associate with the advertised connected route. |
|
Step 9 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
|
Step 10 |
show isis [ ipv4 | ipv6 | afi-all ] [ unicast | safi-all ] route [ detail ] Example: |
Displays tag information. Verify that all tags are present in the RIB. |
This optional task describes how to set the priority (order) for which specified prefixes are added to the RIB. The prefixes can be chosen using an access list (ACL), prefix list, or by matching a tag value.
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
router isis instance-id Example: |
Enables IS-IS routing for the specified routing process, and places the router in router configuration mode. In this example, the IS-IS instance is called isp. |
|
Step 3 |
address-family { ipv4 | ipv6 } [ unicast ] Example: |
Specifies the IPv4 or IPv6 address family, and enters router address family configuration mode. |
|
Step 4 |
metric-style wide [ transition ] [ level { 1 | 2 }] Example: |
Configures a router to generate and accept only wide-link metrics in the Level 1 area. |
|
Step 5 |
spf prefix-priority [ level { 1 | 2 }] { critical | high | medium } { access-list-name | tag tag } Example: |
Installs all routes tagged with the value 3 first. |
|
Step 6 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
This optional task describes how to enable the IP fast reroute (IPFRR) loop-free alternate (LFA) computation to converge traffic flows around link failures.
Note |
To enable node protection on broadcast links, IPFRR and bidirectional forwarding detection (BFD) must be enabled on the interface under IS-IS. |
Note |
IPFRR is supported on the Cisco IOS XR. IPv4 address families and single-level interfaces are supported. Multiprotocol Label Switching (MPLS) FRR and IPFRR cannot be configured on the same interface simultaneously. |
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
router isis instance-id Example: |
Enables IS-IS routing for the specified routing process, and places the router in router configuration mode. In this example, the IS-IS instance is called isp. |
|
Step 3 |
interface type interface-path-id Example: |
Enters interface configuration mode. |
|
Step 4 |
circuit-type { level-1 | level-1-2 | level-2-only } Example: |
(Optional) Configures the type of adjacency. |
|
Step 5 |
address-family ipv4 unicast Example: |
Specifies the IPv4 address family, and enters router address family configuration mode. |
|
Step 6 |
ipfrr lfa { level { 1 | 2 }} Example: |
Specifies the IP fast reroute loop-free alternate computation on link or node failures. |
|
Step 7 |
ipfrr lfa exclude interface type interface-path-id Example: |
(Optional) Excludes an interface from the IP fast reroute loop-free alternate computation. |
|
Step 8 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
This task describes how to activate IS-IS overload bit avoidance.
The IS-IS overload bit avoidance feature is valid only on networks that support the following Cisco IOS XR features:
MPLS
IS-IS
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
mpls traffic-eng path-selection ignore overload Example: |
Activates IS-IS overload bit avoidance. |
A shared risk link group (SRLG) is a set of links sharing a common resource and thus shares the same risk of failure. The existing loop-free alternate (LFA) implementations in interior gateway protocols (IGPs) support SRLG protection. However, the existing implementation considers only the directly connected links while computing the backup path. Hence, SRLG protection may fail if a link that is not directly connected but shares the same SRLG is included while computing the backup path. Global weighted SRLG protection feature provides better path selection for the SRLG by associating a weight with the SRLG value and using the weights of the SRLG values while computing the backup path.
To support global weighted SRLG protection, you need information about SRLGs on all links in the area topology. You can flood SRLGs for remote links using ISIS or manually configuring SRLGS on remote links.
There are three types of configurations that are supported for the global weighted SRLG protection feature.
local SRLG with global weighted SRLG protection
remote SRLG flooding
remote SRLG static provisioning
This example shows how to configure the local SRLG with global weighted SRLG protection feature.
RP/0/RP0/CPU0:router(config)# srlg
RP/0/RP0/CPU0:router(config-srlg)# interface TenGigE0/0/0/0
RP/0/RP0/CPU0:router(config-srlg-if)# name group1
RP/0/RP0/CPU0:router(config-srlg-if)# exit
RP/0/RP0/CPU0:router(config-srlg)# interface TenGigE0/0/0/1
RP/0/RP0/CPU0:router(config-srlg-if)# name group1
RP/0/RP0/CPU0:router(config-srlg)# name group value 100
RP/0/RP0/CPU0:router(config)# router isis 1
RP/0/RP0/CPU0:router(config-isis)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-isis-if-af)# fast-reroute per-prefix srlg-protection weighted-global
RP/0/RP0/CPU0:router(config-isis-if-af)# fast-reroute per-prefix tiebreaker srlg-disjoint index 1
RP/0/RP0/CPU0:router(config-isis)# interface TenGigE0/0/0/0
RP/0/RP0/CPU0:router(config-isis-if)# point-to-point
RP/0/RP0/CPU0:router(config-isis-if)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-isis-if-af)# fast-reroute per-prefix
RP/0/RP0/CPU0:router(config-isis-if-af)# fast-reroute per-prefix ti-lfa
RP/0/RP0/CPU0:router(config-isis)# srlg
RP/0/RP0/CPU0:router(config-isis-srlg)# name group1
RP/0/RP0/CPU0:router(config-isis-srlg-name)# admin-weight 5000
This example shows how to configure the global weighted SRLG protection feature with remote SRLG flooding.The configuration includes local and remote router configuration. On the local router, the global weighted SRLG protection is enabled by using the fast-reroute per-prefix srlg-protection weighted-global command. In the remote router configuration, you can control the SRLG value flooding by using the advertise application lfa link-attributes srlg command. You should also globally configure SRLG on the remote router.
The local router configuration for global weighted SRLG protection with remote SRLG flooding is as follows:
RP/0/RP0/CPU0:router(config)# router isis 1
RP/0/RP0/CPU0:router(config-isis)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-isis-if-af)# fast-reroute per-prefix srlg-protection weighted-global
RP/0/RP0/CPU0:router(config-isis-if-af)# fast-reroute per-prefix tiebreaker srlg-disjoint index 1
RP/0/RP0/CPU0:router(config-isis-if-af)# exit
RP/0/RP0/CPU0:router(config-isis)# interface TenGigE0/0/0/0
RP/0/RP0/CPU0:router(config-isis-if)# point-to-point
RP/0/RP0/CPU0:router(config-isis-if)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-isis-if-af)# fast-reroute per-prefix
RP/0/RP0/CPU0:router(config-isis-if-af)# fast-reroute per-prefix ti-lfa
RP/0/RP0/CPU0:router(config-isis-if-af)# exit
RP/0/RP0/CPU0:router(config-isis)# srlg
RP/0/RP0/CPU0:router(config-isis-srlg)# name group1
RP/0/RP0/CPU0:router(config-isis-srlg-name)# admin-weight 5000
The remote router configuration for global weighted SRLG protection with remote SRLG flooding is as follows:
RP/0/RP0/CPU0:router(config)# srlg
RP/0/RP0/CPU0:router(config-srlg)# interface TenGigE0/0/0/0
RP/0/RP0/CPU0:router(config-srlg-if)# name group1
RP/0/RP0/CPU0:router(config-srlg-if)# exit
RP/0/RP0/CPU0:router(config-srlg)# interface TenGigE0/0/0/1
RP/0/RP0/CPU0:router(config-srlg-if)# name group1
RP/0/RP0/CPU0:router(config-srlg)# name group value 100
RP/0/RP0/CPU0:router(config-srlg)# exit
RP/0/RP0/CPU0:router(config)# router isis 1
RP/0/RP0/CPU0:(config-isis)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-isis-af)# advertise application lfa link-attributes srlg
This example shows configuring the global weighted SRLG protection feature with static provisioning of SRLG values for remote links. You should perform these configurations on the local router.
RP/0/RP0/CPU0:router(config)# srlg
RP/0/RP0/CPU0:router(config-srlg)# interface TenGigE0/0/0/0
RP/0/RP0/CPU0:router(config-srlg-if)# name group1
RP/0/RP0/CPU0:router(config-srlg-if)# exit
RP/0/RP0/CPU0:router(config-srlg)# interface TenGigE0/0/0/1
RP/0/RP0/CPU0:router(config-srlg-if)# name group1
RP/0/RP0/CPU0:router(config-srlg)# name group value 100
RP/0/RP0/CPU0:router(config-srlg)# exit
RP/0/RP0/CPU0:router(config)# router isis 1
RP/0/RP0/CPU0:router(config-isis)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-isis-if-af)# fast-reroute per-prefix srlg-protection weighted-global
RP/0/RP0/CPU0:router(config-isis-if-af)# fast-reroute per-prefix tiebreaker srlg-disjoint index 1
RP/0/RP0/CPU0:router(config-isis)# interface TenGigE0/0/0/0
RP/0/RP0/CPU0:router(config-isis-if)# point-to-point
RP/0/RP0/CPU0:router(config-isis-if)# address-family ipv4 unicast
RP/0/RP0/CPU0:router(config-isis-if-af)# fast-reroute per-prefix
RP/0/RP0/CPU0:router(config-isis-if-af)# fast-reroute per-prefix ti-lfa
RP/0/RP0/CPU0:router(config-isis)# srlg
RP/0/RP0/CPU0:router(config-isis-srlg)# name group1
RP/0/RP0/CPU0:router(config-isis-srlg-name)# admin-weight 5000
RP/0/RP0/CPU0:router(config-isis-srlg-name)# static ipv4 address 10.0.4.1 next-hop ipv4 address 10.0.4.2
RP/0/RP0/CPU0:router(config-isis-srlg-name)# static ipv4 address 10.0.4.2 next-hop ipv4 address 10.0.4.1 The ISIS Link-Group feature allows you to define a group or set of links, and raise or lower their ISIS metric according to a predefined number of active links.
When the total number of active links (in terms of ISIS adjacency) in a group falls below the configured number or members, a predefined offset is applied on the remaining active links. When the total number of active links in a group is reverted, ISIS restores the configured metric by removing the offset.
In the example below, Router A has to exit through router B and C. In between A and B there are two layer 3 links with the same ISIS metric (20). There is a similar setup between A and C (30). In normal operations, the traffic from A goes through B. If the ISIS Link-Group is not configured, even when the link between A and B fails, traffic is still routed through B. However, with ISIS Link-Group, you can set an offset of 20 with minimum-members of 2. Thus, if a link between A and B fails, the metric is raised to 40 (configured (20) + offset (20)), and so the traffic is routed to C. Further, you can define another ISIS Link-Group, this time between A and C. If a link between B and C fails, you can raise the offset to 20, and thus traffic is routed back to B.
Perform this task to configure Intermediate System-to-Intermediate System (IS-IS) link group profiles:
| Command or Action | Purpose | |||
|---|---|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
||
|
Step 2 |
router isis instance-id Example: |
Enters IS-IS configuration submode. |
||
|
Step 3 |
link-group link-group-name { [ metric-offset count | maximum ] | [ minimum-members count | revert-members count ] } |
|
||
|
Step 4 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
||
|
Step 5 |
show isis interface Example: |
(Optional) If link-group is configured on the interface, when showing the IS-IS interface-related topology, this command displays the link-group and current offset-metric value. |
||
|
Step 6 |
show isis lsp Example: |
(Optional) Displays the updated metric value. |
The following is an example configuration, along with the show isis interface output:
router isis 1
is-type level-2-only
net 49.1111.0000.0000.0006.00
link-group foo
metric-offset 100
revert-members 4
minimum-members 2
!
address-family ipv4 unicast
metric-style wide
!
interface GigabitEthernet0/0/0/1
point-to-point
address-family ipv4 unicast
link-group foo
RP/0/RSP0/CPU0:Iguazu#sh isis interface gig 0/0/0/1
Thu Jun 11 14:55:32.565 CEST
GigabitEthernet0/0/0/1 Enabled
Adjacency Formation: Enabled
Prefix Advertisement: Enabled
IPv4 BFD: Disabled
IPv6 BFD: Disabled
BFD Min Interval: 150
BFD Multiplier: 3
Circuit Type: level-2-only (Interface circuit type is level-1-2)
Media Type: P2P
Circuit Number: 0
Extended Circuit Number: 36
Next P2P IIH in: 8 s
LSP Rexmit Queue Size: 0
Level-2
Adjacency Count: 1
LSP Pacing Interval: 33 ms
PSNP Entry Queue Size: 0
CLNS I/O
Protocol State: Up
MTU: 1497
SNPA: 0026.9829.af19
Layer-2 MCast Groups Membership:
All ISs: Yes
IPv4 Unicast Topology: Enabled
Adjacency Formation: Running
Prefix Advertisement: Running
Metric (L1/L2): 110/110
Weight (L1/L2): 0/0
MPLS Max Label Stack: 1
MPLS LDP Sync (L1/L2): Disabled/Disabled
Link-Group (L1/L2): Configured/Configured
Metric-Offset (L1/L2):100/100
IPv4 Address Family: Enabled
Protocol State: Up
Forwarding Address(es): 100.5.6.6
Global Prefix(es): 100.5.6.0/24
LSP transmit timer expires in 0 ms
LSP transmission is idle
Can send up to 9 back-to-back LSPs in the next 0 ms
Note |
One IS-IS interface and address-family can specify only one link-group association. The default is for both levels regardless of the current circuit-type. The link-group association can be specified for one level only if configured. |
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters global configuration mode. |
|
Step 2 |
router isis instance-id Example: |
Enters IS-IS configuration submode. |
|
Step 3 |
interface type interface-path-id Example: |
Enters interface configuration mode. |
|
Step 4 |
address-family ipv4 | ipv6 [ unicast ] Example: |
Specifies the IPv6 address family and enters router address family configuration mode.
|
|
Step 5 |
link-group link-group-name [ level { 1 | 2 } ] Example: |
Specifies the link-group name and sets the tag at the level specified. |
|
Step 6 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
|
Step 7 |
show isis interface Example: |
(Optional) If link-group is configured on the interface, when showing the IS-IS interface-related topology, this command displays the link-group value. |
The IS-IS Max Metric on Startup feature allows IS-IS to advertise the maximum metric during the start-up phase. The feature allows the advertisement until either BGP converges or the specified start-up timer expires.
When you configure a router with maximum metric value on start-up, IS-IS advertises the maximum metric value for IS-IS links. IS-IS also advertises the prefixes that originated from the routers. This configuration makes the neighboring routers use this router as a transit-node of last resort. The router advertises the maximum metric only during the start-up phase when the routing table has not converged. The router advertises the normal metric values when the start-up timer expires or when the router receives the BGP converge signal. You can set maximum metric for default routes, SRv6 locator, or redistributed prefixes.
For narrow metrics, the maximum metric value is 63; for wide metrics, the maximum metric value is 16777214.
Router(config)# router isis 1
Router(config-isis)# max-metric level 2
Router(config-isis)# is-type level-2-only
Router(config-isis)# net 49.0001.0000.0000.0100.00
Router(config-isis)# nsr
Router(config-isis)# nsf cisco
Router(config-isis)# address-family ipv4 unicast
Router(config-isis-af)# metric-style wide
Router(config-isis-af)# mpls traffic-eng level-2-only
Router(config-isis-af)# mpls traffic-eng router-id Loopback 0
Router(config-isis-af)# default-information originate
Router(config-isis-af)# redistribute static
Router(config-isis-af)# exit
Router(config-isis)# address-family ipv6 unicast
Router(config-isis-af)# metric-style wide
Router(config-isis-af)# srv6
Router(config-isis-af)# locator abc
Router(config-isis-af)# exit
Router(config-isis)# interface Loopback 0
Router(config-isis-if)# address-family ipv4 unicast
Router(config-isis-if-af)# exit
Router(config-isis)# address-family ipv6 unicast
Router(config-isis-af)# exit
Router(config-isis)# interface GigabitEthernet0/0/0/2
Router(config-isis-if)# address-family ipv4 unicast
Router(config-isis-if-af)# exit
Router(config-isis-if)# address-family ipv6 unicast
router isis 1
max-metric on-startup wait-for-bgp default-route external interlevel srv6-locator level 2
is-type level-2-only
net 49.0001.0000.0000.0100.00
nsr
nsf cisco
address-family ipv4 unicast
metric-style wide
mpls traffic-eng level-2-only
mpls traffic-eng router-id Loopback0
default-information originate
redistribute static
!
address-family ipv6 unicast
metric-style wide
srv6
locator abc
!
!
!
interface Loopback0
address-family ipv4 unicast
!
address-family ipv6 unicast
!
!
interface GigabitEthernet0/0/0/2
address-family ipv4 unicast
!
address-family ipv6 unicast
!
!
!
|
Feature Name |
Release Information |
Feature Description |
|---|---|---|
|
IS-IS protocol shutdown mode |
Release 24.4.1 |
You can now gracefully shut down IS-IS on an interface or router without abruptly interrupting network operations. This feature simplifies operations by consolidating multiple steps into a single command, ensuring network stability during maintenance or configuration changes. This feature introduces these changes: CLI: YANG Data Model:
|
The IS-IS protocol shutdown mode feature introduces the protocol shutdown command that allows you to gracefully shut down the IS-IS Protocol. This command eliminates the need to manually set the overload-bit and shut down each live interface.
When you use this command, the system
sets the overload-bit and floods local link-state packets (LSP) to all neighbors,
disables all active IS-IS interfaces (except the Non Stop Routing (NSR) interface),
maintains the IS-IS local LSP database and other local data structures intact, and
ensures that there are no IS-IS adjacency or routes for forwarding traffic.
The no form of the command reverses these actions:
Clears the overload-bit and floods local LSP to all neighbors.
Enables all live IS-IS interfaces (except NSR interface).
The IS-IS protocol shutdown mode feature provides these benefits:
Simplifies maintenance by consolidating multiple steps into a single command.
Reduces the risk of manual errors during configuration changes.
Maintains local LSP database and data structures intact, ensuring a smoother return to operation.
Provides a consistent operational procedure across different protocols (similar to OSPF and OSPFv3).
|
Step 1 |
Enable IS-IS protocol shutdown mode. Example:To disable the IS-IS protocol shutdown mode, use the no protocol shutdown command. |
|
Step 2 |
Verify that the IS-IS protocol shutdown mode is successfully enabled. Example: |
|
Step 3 |
Verify that the IS-IS interface is shown as disabled when it is in protocol shutdown state. Example: |
|
Feature Name |
Release Information |
Feature Description |
|
IS-IS Cost Fallback on IOS XR Bundle-Ether Interface |
Release 7.3.1 |
This feature enables you to effectively manage the capacity of the network across Bundle-Ether interfaces through a cost fallback mechanism. This mechanism increases the Bundle-Ether interface metric based on a active or total threshold. The threshold is a percentage of bandwidth. |
The IS-IS Cost Fallback on IOS XR Bundle-Ether Interface feature enables you to effectively manage the capacity of the network across the Bundle-Ether interfaces through a cost fallback mechanism. This mechanism increases the Bundle-Ether interface metric based on a active or total threshold. The threshold is a percentage of bandwidth.
Threshold = Bandwidth of the active bundle member links / the total bandwidth of all bundle links including both active and nonnative links.
The threshold based on the percentage of bandwidth makes it unnecessary to configure the changes as you upgrade the bandwidth.
Router(config)# router isis 1
Router(config-isis)# is-type level-2-only
Router(config-isis)# net 47.0000.0000.0002.00
Router(config-isis)# log adjacency changes
Router(config-isis)# address-family ipv4 unicast
Router(config-isis-af)# exit
Router(config-isis)# address-family ipv6 unicast
Router(config-isis-af)# metric-style wide
Router(config-isis-af)# segment-routing mpls sr-prefer
Router(config-isis-af)# exit
Router(config-isis)# interface Bundle-Ether1
Router(config-isis)# address-family ipv4 unicast
Router(config-isis-af)# metric 6 level 1
Router(config-isis-af)# metric 21 level 2
Router(config-isis-af)# metric fallback bandwidth multiplier <1-100> threshold <1-100>
Router(config-isis-af)# exit
Router(config-isis)# address-family ipv6 unicast
Router(config-isis-af)# metric 30 level 1
Router(config-isis-af)# metric 60 level 2
Router(config-isis-af)# metric fallback bandwidth multiplier <factor; 20> threshold <# bandwidth percentage; 80>
router isis 1
is-type level-2-only
net 47.0000.0000.0002.00
log adjacency changes
address-family ipv4 unicast
!
address-family ipv6 unicast
metric-style wide
segment-routing mpls sr-prefer
!
interface Bundle-Ether1
point-to-point
address-family ipv4 unicast
metric 6 level 1
metric 21 level 2
metric fallback bandwidth multiplier <1-100> threshold <1-100>
!
address-family ipv6 unicast
metric 30 level 1
metric 60 level 2
metric fallback bandwidth multiplier <factor; 20> threshold <# bandwidth percentage; 80>
!
Router# show isis interface Bundle-Ether1
!!
Bandwidth: 10000000
Total bandwidth: 20000000
.
IPv4 Unicast Topology: Enabled
Adjacency Formation: Running
Prefix Advertisement: Running
Policy (L1/L2): -/-
Metric (L1/L2): 18/63
Metric fallback:
Bandwidth (L1/L2): Active/Active
Anomaly (L1/L2): Inactive/Inactive
Weight (L1/L2): 0/0
.
IPv6 Unicast Topology: Enabled
Adjacency Formation: Running
Prefix Advertisement: Running
Policy (L1/L2): -/-
Metric (L1/L2): 600/1200
Metric fallback:
Bandwidth (L1/L2): Active/Active
Anomaly (L1/L2): Inactive/Inactive
Weight (L1/L2): 0/0
!!
The show output given below displays the information on IS-IS database.
Router# show isis database detail R2
Mon Jun 8 09:16:12.316 PDT
IS-IS 1 (Level-1) Link State Database
!!
Metric: 600 MT (IPv6 Unicast) IPv6 10:0:13::/112
Metric: 18 IP 10.0.13.0/24
Total Level-1 LSP count: 1 Local Level-1 LSP count: 1
IS-IS 1 (Level-2) Link State Database
Metric: 1200 MT (IPv6 Unicast) IPv6 10:0:13::/112
Metric: 63 IP 10.0.13.0/24
Total Level-2 LSP count: 2 Local Level-2 LSP count: 1
!!
Note |
For information on configuring the link delay anomaly threshold values, refer to Link Anomaly Detection with IGP Penalty in the Segment Routing Configuration Guide. |
When you configure Link Anomaly Detection in SR-PM, PM sets an anomaly bit (A-bit). When IGP receives the A-bit, IGP can automatically increase the IGP metric of the link by a user-defined amount (IGP penalty). This updated IGP metric is advertised in the network to make this link undesirable or unusable. When the link recovers, PM resets the A-bit.
Note |
When node is reloaded, the default or configured IGP metric (without penalty) is advertised until a new measurement is available. |
RP/0/RSP0/CPU0:ios(config)# router isis 100
RP/0/RSP0/CPU0:ios(config-isis)# interface GigabitEthernet 0/1/0/1
RP/0/RSP0/CPU0:ios(config-isis-if)# address-family ipv4 unicast
RP/0/RSP0/CPU0:ios(config-isis-if-af)# metric fallback anomaly delay increment 25
RP/0/RSP0/CPU0:ios(config-isis-if-af)# exit
RP/0/RSP0/CPU0:ios(config-isis-if)# exit
RP/0/RSP0/CPU0:ios(config-isis)# interface GigabitEthernet 0/1/0/2
RP/0/RSP0/CPU0:ios(config-isis-if)# address-family ipv4 unicast
RP/0/RSP0/CPU0:ios(config-isis-if-af)# metric fallback anomaly delay multiplier 2
router isis 100
interface GigabitEthernet0/1/0/1
address-family ipv4 unicast
metric fallback anomaly delay increment 25
!
!
interface GigabitEthernet0/1/0/2
address-family ipv4 unicast
metric fallback anomaly delay multiplier 2
!
!
!
|
Feature Name |
Release Name |
Description |
|---|---|---|
| Protect IS-IS Processes in OOR Conditions | Release 24.2.1 |
This feature enables prompt alerts for out-of-resource conditions in IS-IS processes that could otherwise cause network instability and disruption due to memory leaks and excessive link-state packets (LSPs). That, in addition, they can disable the overload bit status flag that's included in the router's LSP to prevent setting of the overload-bit, but it's not recommended without Cisco consultation This ability to protect IS-IS processes in OOR conditions is enabled by default and you can't disable it. Previously, during OOR conditions, IS-IS processes restarted themselves, but the OOR conditions could persist. The feature introduces these changes: CLI:
YANG Data Model
(see GitHub, YANG Data Models Navigator) |
Out of Resource (OOR) condition is a scenario where an IS-IS process consumes more memory than its data resource limit permits. Under this condition, the IS-IS process actively restarts itself. Despite this restart, the excessive memory consumption issue may continue to occur. This feature actively monitors and alerts users to OOR conditions, proposing corrective measures and reduces network downtime by preemptively addressing OOR-related disruptions.
The IS-IS Protection Enhancements in OOR Conditions feature is enabled by default.
Memory leaks occur when the IS-IS process fails to release memory that is no longer needed. This inefficiency can cause the memory usage to grow slowly and steadily. Without intervention, this incremental growth can eventually consume all available memory resources, leading the IS-IS process into an OOR state. Such a state can significantly degrade network performance or even cause network failures.
To counteract memory leaks, this feature incorporates a mechanism to restart the IS-IS process. The restart clears the accumulated leaked memory, preventing the OOR condition. It effectively resets the process's memory state to clean slate.
The IS-IS protocol employs Nonstop Forwarding (NSF) to maintain uninterrupted network operation during the process restart. NSF ensures that the forwarding of packets continues seamlessly, as the routing state is preserved across the restart. This means that neither end users nor services experience any perceptible disruption during the remediation of the memory leak.
An excessive number of LSPs can flood the IS-IS process, usually due to configuration errors. This typically occurs when multiple nodes redistribute too many prefixes from another routing protocol into IS-IS simultaneously. This overabundance of Link-State Packets (LSPs) can overburden the router's processing capacity and memory, leading to the installation of an unsustainable number of routes into the RIB.
If the IS-IS process attempts to accommodate an extraordinary volume of routes—potentially in the millions—it may exhaust system resources and enter an OOR state. This can result in route installation failures, suboptimal routing, and possibly network instability or collapse.
The feature introduces control mechanisms to manage and regulate the flow of LSPs into the IS-IS process. By monitoring and potentially restricting the number of routes accepted or redistributed into IS-IS, the feature prevents system overload. These controls ensure routing process stability and allow the RIB to handle the route volume without compromising network performance.
IS-IS includes a functionality that regularly checks its memory usage, like a self-check. It monitors its usage against the maximum allowed memory (RLIMIT_DATA). If the memory usage approaches the threshold, IS-IS alerts the main thread, indicating high memory usage. On receiving this alert, the thread initiates action.
The IS-IS memory state is based on the current percentage usage of defined resource limit, which ranges from approximately 1.6 GB to 2.0 GB.
The table below categorizes memory usage into four states based on percentage usage and specifies the corresponding periodic monitoring intervals in seconds for each state.
|
Memory Usage (%) |
Memory State |
Periodic Monitoring Interval in Seconds |
|---|---|---|
|
Less than 80 |
Normal |
60 |
|
Greater than or equal to 80 and less than 90 |
Minor |
30 |
|
Greater than or equal to 90 and less than 95 |
Severe |
20 |
|
Greater than or equal to 95 |
Critical |
10 |
When the memory state is not 'Normal', IS-IS actively suppresses the computation and installation of Fast Reroute (FRR) backup paths to the Routing Information Base (RIB). Once the memory state returns to 'Normal' and remains stable for 180 seconds, IS-IS recommences the standard FRR computation and proceeds with installing FRR backup paths.
If IS-IS identifies a memory leak as the cause of the OOR condition, it initiates a process restart. The process restart does not trigger RP failover even if the nsr process-failures switchover is configured.
If IS-IS determines that the OOR condition does not stem from a memory leak, it enters the 'waiting state' as specified in ISO-10589. This action sets the overload bit in the LSP database for both levels.
In waiting state, the router accepts and processes existing LSPs, including purges. It accepts new LSPs but does not store or process them.
Normal notification signifies a return to normal memory usage. If IS-IS is in the 'waiting state', it initiates a 60-second timer called as OORWaitingTimer. Receipt of any OOR notification other than 'Normal' cancels the OORWaitingTimer. IS-IS exits the 'waiting state' only when the OORWaitingTimer expires, indicating that memory usage has remained normal for 60 seconds.
Upon exiting the 'waiting state', IS-IS clears the overload bit in the LSP database for both levels, in compliance with ISO 10589. To accelerate the exchange of LSPs, IS-IS executes a one-time send of a Complete Sequence Number PDU (CSNP) across each IS-IS interface, whether LAN or point-to-point, applying a jitter of up to 10 seconds.
|
Feature Name |
Release Name |
Description |
|---|---|---|
| LSP Fast-Flooding on IS-IS Networks | Release 24.3.1 |
You can now accelerate the rate at which Link State Packets (LSPs) are distributed across an IS-IS network. Faster LSP distribution means faster network convergence. This faster convergence ensures that the most accurate topology information is quickly available across all routers on the network, reducing the chances of routing loops or misrouting. The feature introduces these changes: CLI: YANG Data Model:
(see GitHub, YANG Data Models Navigator) |
The LSP Fast-Flooding on IS-IS Networks feature increases the transmission of Link State Packets (LSPs) within an IS-IS domain. By boosting the flooding rate of LSPs, this feature facilitates quicker distribution of network topology data, aiding the network in adapting more swiftly to modifications. Network administrators can set up the feature to dispatch LSPs in bursts, targeting a default rate of 1000 LSPs per second, which is significantly higher than the conventional rate. The feature also modulates the sending rate based on the neighbor's capacity to process and acknowledge the LSPs, ensuring effective communication and preventing congestion.
Unlike traditional IS-IS flooding, which functions on a fixed timer, the IS-IS Fast Flooding of LSPs feature provides adaptability and control. It encompasses several adjustable parameters accessible through commands, such as settings for the local Partial Sequence Number PDU (PSNP) interval and the maximum flooding rate, which can be modified according to particular network requirements. This feature is inactive by default, permitting network administrators to activate it selectively where the network infrastructure will gain from improved LSP flooding capabilities. This selective activation is essential for maintaining optimal performance across various network topologies and situations.
The IS-IS Fast Flooding of LSPs feature incorporates real-time adjustment of the LSP flooding rate. This dynamic modification is based on persistent monitoring of the acknowledgment rates from neighboring routers through PSNP receipts. When the feature identifies delays in acknowledgment, it automatically decreases the flooding rate to avoid overloading the neighbor's processing capabilities. Conversely, if acknowledgments are received promptly, the feature may elevate the flooding rate up to the configured maximum, enhancing the speed of topology distribution. This adaptive method ensures that the feature reacts appropriately to the operational conditions of the network, providing an optimal balance between fast convergence and network stability. Network administrators can utilize this information to fine-tune the feature's parameters, ensuring that the flooding rate is both efficient and sustainable.
This section provides the following configuration examples:
The following example shows single-topology mode being enabled. An IS-IS instance is created, the NET is defined, IPv6 is configured along with IPv4 on an interface, and IPv4 link topology is used for IPv6.
This configuration allows POS interface 0/3/0/0 to form adjacencies for both IPv4 and IPv6 addresses.
router isis isp
net 49.0000.0000.0001.00
address-family ipv6 unicast
single-topology
interface POS0/3/0/0
address-family ipv4 unicast
!
address-family ipv6 unicast
!
exit
!
interface POS0/3/0/0
ipv4 address 10.0.1.3 255.255.255.0
ipv6 address 2001::1/64
The following example shows multitopology IS-IS being configured in IPv6.
router isis isp
net 49.0000.0000.0001.00
interface POS0/3/0/0
address-family ipv6 unicast
metric-style wide level 1
exit
!
interface POS0/3/0/0
ipv6 address 2001::1/64
The following example shows usage of the set- attached-bit and redistribute commands. Two instances, instance “1” restricted to Level 1 and instance “2” restricted to Level 2, are configured.
The Level 1 instance is propagating routes to the Level 2 instance using redistribution. Note that the administrative distance is explicitly configured higher on the Level 2 instance to ensure that Level 1 routes are preferred.
Attached bit is being set for the Level 1 instance since it is redistributing routes into the Level 2 instance. Therefore, instance “1” is a suitable candidate to get from the area to the backbone.
router isis 1
is-type level-2-only
net 49.0001.0001.0001.0001.00
address-family ipv4 unicast
distance 116
redistribute isis 2 level 2
!
interface GigabitEthernet 0/3/0/0
address-family ipv4 unicast
!
!
router isis 2
is-type level-1
net 49.0002.0001.0001.0002.00
address-family ipv4 unicast
set
-attached
-bit
!
interface GigabitEthernet 0/1/0/0
address-family ipv4 unicast
The following example shows how to tag routes.
route-policy isis-tag-55
end-policy
!
route-policy isis-tag-555
if destination in (5.5.5.0/24 eq 24) then
set tag 555
pass
else
drop
endif
end-policy
!
router static
address-family ipv4 unicast
0.0.0.0/0 2.6.0.1
5.5.5.0/24 Null0
!
!
router isis uut
net 00.0000.0000.12a5.00
address-family ipv4 unicast
metric-style wide
redistribute static level-1 route-policy isis-tag-555
spf prefix-priority critical tag 13
spf prefix-priority high tag 444
spf prefix-priority medium tag 777
The following example shows how to activate IS-IS overload bit avoidance:
config
mpls traffic-eng path-selection ignore overload
The following example shows how to deactivate IS-IS overload bit avoidance:
config
no mpls traffic-eng path-selection ignore overload
This section describes an example for configuring IS-IS to handle overloading of routers, without setting the overload bit.
When a router is configured with the IS-IS overload bit, it participates in the routing process when the overload bit is set, but does not forward traffic (except for traffic to directly connected interfaces). To configure the overload behavior for IS-IS, without setting the overload bit, configure the max-link-metric statement. By configuring this statement, the router participates in the routing process and is used as a transit node of last resort.
Ensure that you are familiar with configuring router interfaces for a given topology.
|
Step 1 |
Configure Routers A, B, and C as shown in the topology. Use the following IP Addresses:
|
|
Step 2 |
Configure IS-IS and the corresponding net addresses on Routers A, B and C. Example: |
|
Step 3 |
Configure IPv4 and IPv6 address families on the loopback interfaces of Routers A, B, and C. Example: |
|
Step 4 |
Configure the link metrics on the router interfaces. Example: |
|
Step 5 |
Confirm your configuration by viewing the route prefixes on Routers A, B, and C. Example: |
|
Step 6 |
Confirm the link metrics on Router B, prior to configuring the max-link-metric statement. Example: |
|
Step 7 |
Configure the max-link-metric statement on Router B. Example: |
|
Step 8 |
Commit your configuration. Example: |
|
Step 9 |
Confirm the change in link metrics on Router B. Example: |
|
Step 10 |
(Optional) Verify the change in route prefixes on Routers A and C. Example: |
IS-IS has been successfully configured to handle router overload without setting the overload bit.
|
Feature Name |
Release |
Description |
|---|---|---|
|
Setting SPF interval in IS-IS to postpone the IS-IS SPF computations |
Release 7.7.1 |
You can now define a standard algorithm to postpone the IS-IS SPF computations by setting an SPF interval. This reduces the computational load and churn on IGP nodes when multiple temporally close network events trigger multiple SPF computations. This algorithm also reduces the probability and the duration of transient forwarding loops during native IS-IS convergence when the protocol reacts to multiple temporally close events. This feature complies with RFC 8405. This feature introduces the spf-interval ietf command. |
You can set an SPF interval in IS-IS to define a standard algorithm to postpone the IS-IS SPF computations off. This reduces the computational load and churn on IGP nodes when multiple temporally close network events trigger multiple SPF computations.
This algorithm reduces the probability and the duration of transient forwarding loops during native IS-IS convergence when the protocol reacts to multiple temporally close events.
To do this, you can use the algorithm specified by RFC 8405 to temporarily postpone the IS-IS SPF computation.
This task is optional.
Enter to the Cisco IOS XR configuration mode.
Router# configureEnable IS-IS routing for the specified routing instance and place the router in router configuration mode.
Router(config)# router isis <tag>Specify the IPv4 or IPv6 address family, and then enters router address family configuration mode.
Router(config-isis)# address-family {ipv4 | ipv6} unicastSet the interval type (IETF) for SPF calculations.
Router(config-isis-af)# spf-interval ietfCommit the changes.
Router(config-isis-af)# commitRouter# configure
Router(config)# router isis isp
Router(config-isis)# address-family ipv4 unicast
Router(config-isis-af)# spf-interval ietf?
initial-wait Initial delay before running a route calculation [50]
short-wait Short delay before running a route calculation [200]
long-wait Long delay before running a route calculation [5000]
learn-interval Time To Learn interval for running a route calculation [500]
holddown-interval Holddown interval for running a route calculation [10000]
level Set SPF interval for one level only
Router(config-isis-af)# spf-interval ietf
Router(config-isis-af)# commit
Router# show run router isis
router isis 1
net 49.0001.0000.0000.0100.00
log adjacency changes
address-family ipv4 unicast
metric-style wide
spf-interval ietf
!
address-family ipv6 unicast
metric-style wide
spf-interval ietf
!
Router(config-isis-af)# spf-interval ietf?
initial-wait Initial delay before running a route calculation [50]
short-wait Short delay before running a route calculation [200]
long-wait Long delay before running a route calculation [5000]
learn-interval Time To Learn interval for running a route calculation [500]
holddown-interval Holddown interval for running a route calculation [10000]
level Set SPF interval for one level only
The following show command displays the output with the new spf-interval algorithm. The output displays the actual delay taken to compute the SPF.
Router# show isis ipv4 spf-log last 5 detail
IS-IS 1 Level 2 IPv4 Unicast Route Calculation Log
Time Total Trig.
Timestamp Type (ms) Nodes Count First Trigger LSP Triggers
------------ ----- ----- ----- ----- -------------------- -----------------------
--- Wed Mar 16 2022 ---
15:31:49.763 FSPF 1 6 3 tb5-r4.00-00 LINKBAD PREFIXBAD
Delay: 101ms (since first trigger)
261177ms (since end of last calculation)
Trigger Link: tb5-r2.00
Trigger Prefix: 34.1.24.0/24
New LSP Arrivals: 0
SR uloop: No
Next Wait Interval: 200ms
RIB Batches: 1 (0 critical, 0 high, 0 medium, 1 low)
Timings (ms): +--Total--+
Real CPU
SPT Calculation: 1 1
Route Update: 0 0
----- -----
It is recommended to use the default delay values, which are listed in Syntax description. These default parameters are suggetsed by RFC 8405. These should be appropriate for most networks.
However, you can configure different values if required.
Router# configure
Router(config)# router isis isp
Router(config-isis)# address-family ipv4 unicast
Router(config-isis-af)# spf-interval ietf
Router(config-isis-af)# commit
Router(config-isis-af)# spf-interval ietf short-wait 500
Router(config-isis-af)# commit
To implement more IP routing protocols, see the following document modules in Routing Configuration Guide for Cisco ASR 9000 Series Routers:
Implementing OSPF
Implementing BGP
Implementing EIGRP
Implementing RIP
The following sections provide references related to implementing IS-IS.
|
Related Topic |
Document Title |
|---|---|
|
IS-IS commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples |
Routing Command Reference for Cisco ASR 9000 Series Routers |
|
MPLS TE feature information |
Implementing MPLS Traffic Engineering on Cisco ASR 9000 Series Router module in MPLS Configuration Guide for Cisco ASR 9000 Series Routers |
|
Bidirectional Forwarding Detection (BFD) |
Interface and Hardware Component Configuration Guide for Cisco ASR 9000 Series Routers and Interface and Hardware Component Command Reference for Cisco ASR 9000 Series Routers |
|
Standards |
Title |
|---|---|
|
Draft-ietf-isis-ipv6-05.txt |
Routing IPv6 with IS-IS, by Christian E. Hopps |
|
Draft-ietf-isis-wg-multi-topology-06.txt |
M-ISIS: Multi Topology (MT) Routing in IS-IS, by Tony Przygienda, Naiming Shen, and Nischal Sheth |
|
Draft-ietf-isis-traffic-05.txt |
IS-IS Extensions for Traffic Engineering, by Henk Smit and Toni Li |
|
Draft-ietf-isis-restart-04.txt |
Restart Signaling for IS-IS, by M. Shand and Les Ginsberg |
|
Draft-ietf-isis-igp-p2p-over-lan-05.txt |
Point-to-point operation over LAN in link-state routing protocols, by Naiming Shen |
|
Draft-ietf-rtgwg-ipfrr-framework-06.txt |
IP Fast Reroute Framework, by M. Shand and S. Bryant |
|
Draft-ietf-rtgwg-lf-conv-frmwk-00.txt |
A Framework for Loop-free Convergence, by M. Shand and S. Bryant |
|
MIBs |
MIBs Link |
|---|---|
| — |
To locate and download MIBs using Cisco IOS XR software, use the Cisco MIB Locator found at the following URL and choose a platform under the Cisco Access Products menu: https://mibs.cloudapps.cisco.com/ITDIT/MIBS/servlet/index |
|
RFCs |
Title |
|---|---|
|
RFC 1142 |
OSI IS-IS Intra-domain Routing Protocol |
|
RFC 1195 |
Use of OSI IS-IS for Routing in TCP/IP and Dual Environments |
|
RFC 2763 |
Dynamic Hostname Exchange Mechanism for IS-IS |
|
RFC 2966 |
Domain-wide Prefix Distribution with Two-Level IS-IS |
|
RFC 2973 |
IS-IS Mesh Groups |
|
RFC 3277 |
IS-IS Transient Blackhole Avoidance |
|
RFC 3373 |
Three-Way Handshake for IS-IS Point-to-Point Adjacencies |
|
RFC 3567 |
IS-IS Cryptographic Authentication |
|
RFC 4444 |
IS-IS Management Information Base |
|
RFC 8405 |
Set SPF interval in IS-IS to postpone the IS-IS SPF computations |
|
Description |
Link |
|---|---|
|
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