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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.
When multiple instances of IS-IS are being run, an interface can be associated with only one instance (process). Instances may not share an interface.
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.
When multiple instances of IS-IS are being run, an interface can be associated with only one instance (process). Instances may not share an interface.
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 and . |
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 example shows how to enter router configuration mode:
RP/0/# configuration
RP/0/(config)# router isis isp
RP/0/(config-isis)#
The following example shows how to enter router address family configuration mode:
RP/0/(config)# router isis isp
RP/0/(config-isis)# address-family
ipv4 u
nicast
RP/0/(config-isis-af)#
The following example shows how to enter interface configuration mode:
RP/0/(config)# router isis isp
RP/0/(config-isis)# interface GigabitEthernet 0
/3/0/0
RP/0/(config-isis-if)#
The following example shows how to enter interface address family configuration mode:
RP/0/(config)# router isis isp
RP/0/(config-isis)# interface
GigabitEthernet 0 /3/0/0
RP/0/(config-isis-if)# address-family ipv4 unicast
RP/0/(config-isis-if-af)#
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. |
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.
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/RP0/CPU0:router(config-isis)# lsp-refresh-interval 1200 level 2
RP/0/RP0/CPU0:router(config-isis)# lsp-refresh-interval 1100 level 1
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Step 1 |
configure Example:Enters mode. |
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Step 2 |
router isis instance-id Example:Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.
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Step 3 |
lsp-refresh-interval seconds [ level { 1 | 2 }] Example:(Optional) Sets the time between regeneration of LSPs that contain different sequence numbers
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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.
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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.
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Step 6 |
lsp-mtu bytes [ level { 1 | 2 }] Example:(Optional) Sets the maximum transmission unit (MTU) size of LSPs. |
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Step 7 |
max-lsp-lifetime seconds [ level { 1 | 2 }] Example:(Optional) Sets the initial lifetime given to an LSP originated by the router.
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Step 8 |
ignore-lsp-errors disable Example:(Optional) Sets the router to purge LSPs received with checksum errors. |
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Step 9 |
interface type interface-path-id Example:Enters interface configuration mode. |
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Step 10 |
lsp-interval milliseconds [ level { 1 | 2 }] Example:(Optional) Configures the amount of time between each LSP sent on an interface. |
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Step 11 |
csnp-interval seconds [ level { 1 | 2 }] Example:(Optional) Configures the interval at which periodic CSNP packets are sent on broadcast interfaces.
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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. |
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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.
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Step 14 |
mesh-group { number | blocked } Example:(Optional) Optimizes LSP flooding in NBMA networks with highly meshed, point-to-point topologies.
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Step 15 |
Use the commit or end command. commit —Saves the configuration changes and remains within the configuration session.
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Step 16 |
show isis interface [ type interface-path-id | level { 1 | 2 }] [ brief ] Example:(Optional) Displays information about the IS-IS interface. |
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Step 17 |
show isis [ instance instance-id ] database [ level { 1 | 2 }] [ detail | summary | verbose ] [ * | lsp-id ] Example:(Optional) Displays the IS-IS LSP database. |
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Step 18 |
show isis [ instance instance-id ] lsp-log [ level { 1 | 2 }] Example:(Optional) Displays LSP log information. |
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Step 19 |
show isis database-log [ level { 1 | 2 }] Example:(Optional) Display IS-IS database log information. |
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 module of .
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.
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 NCS 5500 Series Routers.
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.
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).
This task explains how to configure authentication for IS-IS. This task is optional.
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Step 1 |
configure Example:Enters mode. |
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Step 2 |
router isis instance-id Example:Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.
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Step 3 |
lsp-password { hmac-md5 | text } { clear | encrypted } password [ level { 1 | 2 }] [ send-only ] [ snp send-only ] Example:Configures the LSP authentication password.
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Step 4 |
interface type interface-path-id Example:Enters interface configuration mode. |
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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. |
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Step 6 |
Use the commit or end command. commit —Saves the configuration changes and remains within the configuration session.
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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.
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Step 1 |
configure Example:Enters mode. |
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Step 2 |
router isis instance-id Example:Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.
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Step 3 |
l sp-password keychain keychain-name [ level { 1 | 2 }] [ send-only ] [ snp send-only ] Example:Configures the keychain. |
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Step 4 |
interface type interface-path-id Example:Enters interface configuration mode. |
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Step 5 |
hello-password keychain keychain-name [ level { 1 | 2 }] [ send-only ] Example:Configures the authentication password for an IS-IS interface. |
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Step 6 |
Use the commit or end command. commit —Saves the configuration changes and remains within the configuration session.
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You can configure up to 16 IS-IS instances. MPLS can run on multiple IS-IS processes as long as the processes run on different sets of interfaces. Each interface may be associated with only a single IS-IS instance. The software prevents the double-booking of an interface by two instances at configuration time—two instances of MPLS configuration causes an error.
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.
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.
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Step 1 |
configure Example:Enters mode. |
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Step 2 |
router isis instance-id Example:Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.
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Step 3 |
net network-entity-title Example:Configures network entity titles (NETs) for the routing instance.
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Step 4 |
is-type { level-1 | level-1-2 | level-2-only } Example:(Optional) Configures the system type (area or backbone router).
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Step 5 |
Use the commit or end command. commit —Saves the configuration changes and remains within the configuration session.
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Step 6 |
show isis [ instance instance-id ] protocol Example:(Optional) Displays summary information about the IS-IS instance. |
Single-topology IPv6 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.
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. |
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Step 1 |
configure Example:Enters mode. |
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Step 2 |
interface type interface-path-id Example:Enters interface configuration mode. |
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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.
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Step 4 |
exit Example:Exits interface configuration mode, and returns the router to mode. |
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Step 5 |
router isis instance-id Example:Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.
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Step 6 |
net network-entity-title Example:Configures NETs for the routing instance.
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Step 7 |
address-family ipv6 [ unicast ] Example:Specifies the IPv6 address family and enters router address family configuration mode.
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Step 8 |
single-topology Example:(Optional) Configures the link topology for IPv4 when IPv6 is configured.
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Step 9 |
exit Example:Exits router address family configuration mode, and returns the router to router configuration mode. |
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Step 10 |
interface type interface-path-id Example:Enters interface configuration mode. |
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Step 11 |
circuit-type { level-1 | level-1-2 | level-2-only } Example:(Optional) Configures the type of adjacency.
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Step 12 |
address-family { ipv4 | ipv6 } [ unicast ] Example:Specifies the IPv4 or IPv6 address family, and enters interface address family configuration mode.
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Step 13 |
Use the commit or end command. commit —Saves the configuration changes and remains within the configuration session.
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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. |
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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. |
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
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.
The incremental SPF algorithm can be enabled separately. When enabled, the incremental shortest path first (ISPF) is not employed immediately. Instead, the full SPF algorithm is used to “seed” the state information required for the ISPF to run. The startup delay prevents the ISPF from running for a specified interval after an IS-IS restart (to permit the database to stabilize). After the startup delay elapses, the ISPF is principally responsible for performing all of the SPF calculations. The reseed interval enables a periodic running of the full SPF to ensure that the iSFP state remains synchronized.
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Step 1 |
configure Example:Enters mode. |
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Step 2 |
router isis instance-id Example:Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.
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Step 3 |
address-family { ipv4 | ipv6 } [ unicast ] Example:Specifies the IPv4or IPv6 address family, and enters router address family configuration mode. |
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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.
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Step 5 |
ispf [ level { 1 | 2 }] Example:(Optional) Configures incremental IS-IS ISPF to calculate network topology. |
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Step 6 |
Use the commit or end command. commit —Saves the configuration changes and remains within the configuration session.
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Step 7 |
show isis [ instance instance-id ] [[ ipv4 | ipv6 | afi-all ] [ unicast | safi-all ]] spf-log [ level { 1 | 2 }] [ ispf | 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.
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Step 1 |
configure Example:Enters mode. |
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Step 2 |
router isis instance-id Example:Enables IS-IS routing for the specified routing process, and places the router in router configuration mode.
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Step 3 |
set-overload-bit [ on-startup { delay | wait-for-bgp }] [ level { 1 | 2 }] Example:(Optional) Sets the overload bit.
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Step 4 |
address-family { ipv4 | ipv6 } [ unicast ] Example:Specifies the IPv4 or IPv6 address family, and enters router address family configuration mode. |
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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.
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Step 6 |
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.
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Step 7 |
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
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Step 8 |
maximum-paths route-number Example:(Optional) Configures the maximum number of parallel paths allowed in a routing table. |
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Step 9 |
distance weight [ address / prefix-length [ route-list-name ]] Example:(Optional) Defines the administrative distance assigned to routes discovered by the IS-IS protocol.
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Step 10 |
set-attached-bit Example:(Optional) Configures an IS-IS instance with an attached bit in the Level 1 LSP. |
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Step 11 |
Use the commit or end command. commit —Saves the configuration changes and remains within the configuration session.
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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 HundredGigE 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 HundredGigE 0/1/0/0
address-family ipv4 unicast
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.
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Step 1 |
configure Example:Enters mode. |
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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. |
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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.
|
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.
This optional task describes how to associate a tag with a connected route of an IS-IS interface.
|
Step 1 |
configure Example:Enters 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. |
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
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. |
This task explains how to configure your router with NSF that allows the 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.
|
Step 1 |
configure Example:Enters 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.
|
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.
|
Step 1 |
configure Example:Enters 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. |
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)# commitThe 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.
This task explains how to configure IS-IS for MPLS TE. This task is optional.
Your network must support the MPLS 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. |
|
Step 1 |
configure Example:Enters 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 |
metric-style wide [ level { 1 | 2 }] Example:Configures a router to generate and accept only wide link metrics in the Level 1 area. |
|
Step 7 |
Use the commit or end command. commit —Saves the configuration changes and remains within the configuration session.
|
|
Step 8 |
show isis [ instance instance-id ] mpls traffic-eng tunnel Example:(Optional) Displays MPLS TE tunnel information. |
|
Step 9 |
show isis [ instance instance-id ] mpls traffic-eng adjacency-log Example:(Optional) Displays a log of MPLS TE IS-IS adjacency changes. |
|
Step 10 |
show isis [ instance instance-id ] mpls traffic-eng advertisements Example:(Optional) Displays the latest flooded record from MPLS TE. |
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.
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.
|
Step 1 |
configure Example:Enters 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. |
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.
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.
|
Step 1 |
configure Example:Enters 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 HundredGigE 0/1/0/3. |
|
Step 6 |
Use the commit or end command. commit —Saves the configuration changes and remains within the configuration session.
|
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.
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 features:
MPLS
IS-IS
|
Step 1 |
configure Example:Enters mode. |
|
Step 2 |
mpls traffic-eng path-selection ignore overload Example:Activates IS-IS overload bit avoidance. |
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
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 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.
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.
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 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 links 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 links or higher cost links 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.
By using the bandwidth command in interface configuration mode .
By adjusting 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.
This set of procedures configures multitopology routing, which is used by PIM for reverse-path forwarding (RPF) path selection.
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.
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 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 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.
|
Step 1 |
configure Example:Enters 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 .
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters 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 . |
|
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.
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 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 enable the IP/LDP fast reroute computation to converge traffic flows around link failures.
Note |
To enable node protection on broadcast links, fast reroute and bidirectional forwarding detection (BFD) must be enabled on the interface under IS-IS. |
| Command or Action | Purpose | |
|---|---|---|
|
Step 1 |
configure Example: |
Enters 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 | ipv6 } [ unicast ] Example: |
Specifies the address family, and enters router address family configuration mode.
|
|
Step 6 |
fast-reroute {per-link | per-prefix } Example: |
|
|
Step 7 |
Do one of the following:
Example:Or |
Configures fast-reroute per-link or per-prefix computation for one level; use either level 1 or level 2. |
|
Step 8 |
Do one of the following:
Example:Or |
Excludes an interface from fast-reroute computation. |
|
Step 9 |
Do one of the following:
Example:Or |
Configures to include an interface to LFA candidate in fast-reroute computation. |
|
Step 10 |
Use the commit or end command. |
commit —Saves the configuration changes and remains within the configuration session.
|
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 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 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. |
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 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
-
-
!
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-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-metric statement. Example: |
|
Step 7 |
Configure the max-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.
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 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.
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.
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