Prerequisites for IP Flexible Algorithm
Configure the data-plane ip command under IGP flex-algo sub-mode to enable participation of the router with the IP Flexible Algorithm.
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Feature Name |
Release Information |
Feature Description |
IGP IP Flexible Algorithm for IS-IS Protocol |
Release 7.6.1 |
With IS-IS protocol extensions supporting Interior Gateway Protocol (IGP) Flexible Algorithm (Flex-Algorithm) on the IP data plane, you can now use the Algorithm to calculate IGP paths in an IP network without running Segment Routing. The IGP Flex-Algorithm allows for user-defined algorithms where the IGP computes paths based on a user-defined combination of metric type and constraints. Earlier, you could calculate IGP only using the Shortest Path First (SPF), which meant that you didn't have any choice except to use the default IGPpath calculated based on a native IGP metric. The following command is introduced: The following commands are modified: |
Flexible Algorithm allows operators to customize IGP shortest path computation according to their own needs. The Flexible Algorithm allows Link State IGPs (OSPF, ISIS) to compute paths using various constraints. Each Flexible Algorithm represents the triplet (Calculation-Type, Metric-Type, Constraints) which all routers in the area consistently elect using the defined selection algorithm.
In IP networks, the router uses IGP Flexible Algorithm by computing the paths to the IPv4 address [RFC0791] and IPv6 address [RFCS8200].
Each interface may be associated with one or more IP addresses, and each IP address may be associated with one Flexible Algorithm.
Packets sent to an address that is associated with a Flexible Algorithm follow the constraint-based path as calculated by the Flexible Algorithm.
Packet sent to an address, that is not associated with a Flexible Algorithm, follow the IGP least-cost path to the egress node.
IGP IP Flexible Algorithm allows forwarding of the voice traffic and data traffic over different paths in the IP network. It can, for example, provide a low latency path for the voice traffic.
This document describes the IS-IS protocol extensions to support IGP Flexible Algorithm in IP networks.
Configure the data-plane ip command under IGP flex-algo sub-mode to enable participation of the router with the IP Flexible Algorithm.
The set consisting of (a) calculation-type, (b) metric-type and (c) a set of constraints is referred to as a Flexible-Algorithm Definition.
Flexible-Algorithm is a numeric identifier in the range 128-255 that is associated via provisioning with the Flexible-Algorithm Definition.
To guarantee the loop free forwarding for paths computed for a particular Flex-Algorithm, all routers that are configured to participate in a particular Flex-Algorithm, and in the same Flex-Algorithm definition advertisement scope must agree on the definition of the Flex-Algorithm as in ietf-lsr-flex-algo.
To guarantee the loop free forwarding for paths computed for a particular Flexible Algorithm, all routers in the network must share the same definition of the Flexible Algorithm. This is achieved by dedicated router(s) advertising the definition of each Flexible Algorithm. Such advertisement is associated with the priority to make sure that all routers agree on a single and consistent definition for each Flexible Algorithm.
Definition of Flexible Algorithm includes:
Metric type
Affinity constraints
Exclude SRLG constraints
To enable the router to advertise the definition for the particular Flexible Algorithm, advertise-definition command is used. At least one router in the area, preferably two for redundancy, must advertise the Flexible Algorithm definition. Without the valid definition being advertised, the Flexible Algorithm are not be functional.
The IPv4 and IPv6 Algorithm Prefix Reachability TLVs defined in draft-ietf-lsr-ip-flexalgo are used to advertise prefix reachability associated with a Flexible Algorithm.
Each application using the Flexible Algorithm must use its own participation signaling. IP Flexible Algorithm uses ISIS IP Algorithm Sub-TLV as specified in draft-ietf-lsr-ip-flexalgo.
Each Flexible Algorithm maintains a separate set of paths—One set per each data-plane.
The IP Flexible Algorithm computation uses only the IP Flex-Algorithm prefixes that are advertised in IPv4 and IPv6 Algorithm Prefix Reachability TLV.
Note |
The performance impact is proportional to the number of IP Flexible Algorithms in the participating router. Routers using the algorithm may use additional CPU cycles to:
|
IP Flexible Algorithm uses the base IPv4 and IPv6 packets for forwarding.
IP Flexible Algorithm prefixes are advertised in IGPs. The forwarding plane installs the IP Flex-Algorithm prefixes advertised by the receiving routers participating in the associated topology and algorithm.
The IP Flex-Algorithm prefixes can be protected by local LFA. When the prefix is associated with an algorithm, the LFA paths to such a prefix are calculated using the Flexible Algorithm in the associated topology. Thus, ensuring that the algorithm follows the same constraints as the calculation of the primary paths.
The IP Flex-Algorithm prefixes can be protected by TI-LFA. For more information on protecting the IP Flex-Algorithm prefixes, see Protecting Flexible Algorithm IP Prefixes.
The following workflow enables IP Flexible Algorithm:
Configure the IP data-plane to participate in the Flexible Algorithm. See Enabling the Flexible Algorithm Participation.
Define the parameters for FAD. See Flexible Algorithm Definitions.
Advertise the definition. See Flexible Algorithm Advertisement.
Define the admin groups. See Configuring Affinity.
Verify the Flexible Algorithm configuration.
Associate the IP address of the interface to the Flexible Algorithm. See Associating the IP Address to Flexible Algorithm.
router isis instance
flex-algo algo
data-plane ip
Note |
Segment Routing is the default data-plane. To use the IP data-plane, you must enable the data-plane ip command. |
The following commands configure the Flexible Algorithm definition under the flex-algo submode configuration:
router isis instance
flex-algo algo
metric-type {delay | te}
affinity {include-any | include-all | exclude-any} name1, name2, …
name—Name of the affinity map.
priority priority value
priority value—Priority used during the Flexible Algorithm definition election.
router isis instance
flex-algo algo
advertise-definition
The following command defines the affinity-map. Affinity-map associates the name with the particular Bit positions in the Extended Admin Group bitmask.
router isis instance
affinity-map name bit-position bit number
Name—Name of the affinity-map.
bit number—Bit position in the Extended Admin Group bitmask.
The following command associates the Flexible Algorithm-specific affinities with an interface:
router isis instance
interface type interface-path-id
affinity flex-algo name 1, name 2, …
name—Name of the affinity-map.
To associate the Flexible Algorithm with the interface global IPv4 or IPv6 address, use the following commands:
ipv4 address prefix-length [secondary | algorithm algo-no]
ipv6 address prefix-length algorithm algo-no]
Note |
If you do not associate an algorithm, the default algorithm value (0) is associated. |
The following example shows how to associate IPv4 address with a Flexible Algorithm for loopback interface 1:
Router(config)# interface loopback 1
Router(config-if#) ipv4 address 1.1.1.1/32
Router(config-if) #ipv4 address 1.1.1.1/32 algorithm 128 ----------> adds the algo value 128
Router(config-if)#commit
The following example associates the IPv6 address with a Flexible Algorithm for loopback interface 0:
Router(config)# interface loopback 0
Router(config-if)# ipv6 address 1::1/64 ---------------> add ipv6 add without algo
Router(config-if)# ipv6 address 1::1/64 algorithm 128 --------> add algo value 128
Router(config-if)#commit
The following figure is a six-node topology from R1 to R6 with configuration.
Node R2 defines the FAD.
IP Flexible Algorithm on node R2 ► R4 ► R3 ►R1.
This example shows the Flexible Algorithm 151 associated to IPv4 address at Loopback interface 51.
RP/0/RSP0/CPU0:Router# show run router isis
router isis 1
is-type level-2-only
net 49.0000.0000.0000.0012.00
affinity-map RED bit-position 4
flex-algo 151
data-plane ip
metric-type delay
advertise-definition
affinity include-any RED
!
!
interface Loopback51
passive
address-family ipv4 unicast
!
address-family ipv6 unicast
This example shows the IP address association with the Flexible Algorithm on Loopback interface 51.
RP/0/RSP0/CPU0:Router# show running interface Loopback 51
Mon Nov 15 14:02:09.832 IST
interface Loopback51
ipv4 address 2.2.2.51 255.255.255.255 algorithm 151
ipv6 address 2:2:2::51/128 algorithm 151
!
RP/0/RSP0/CPU0:Router# show running interface HundredGigE 0/1/0/0.301
Mon Nov 15 14:02:38.800 IST
interface HundredGigE0/1/0/0.301
ipv4 address 200.3.2.1 255.255.255.0 secondary algorithm 151
ipv6 address 200::3:2:1/112 algorithm 151
encapsulation dot1q 301
Use the show isis flex-algo algo-no to verify data-plane used with Flexible Algorithm configuration.
RP/0/RSP0/CPU0:RouterR2# show isis flex-algo 151
Mon Nov 15 15:54:06.291 IST
IS-IS 1 Flex-Algo Database
Flex-Algo 151:
Level-2:
Definition Priority: 128
Definition Source: Router.00, (Local)
Definition Equal to Local: Yes
Definition Metric Type: Delay
Definition Flex-Algo Prefix Metric: No
Exclude Any Affinity Bit Positions:
Include Any Affinity Bit Positions: 4
Include All Affinity Bit Positions:
Exclude SRLGs:
Disabled: No
Local Priority: 128
FRR Disabled: No
Microloop Avoidance Disabled: No
Data Plane Segemnt Routing: No
Data Plane IP: Yes
This example verifies the IP Algo Prefix Advertisements in ISIS database on R2.
RP/0/RP0/CPU0:RouterR1# show isis database detail verbose RouterR2
Mon Nov 15 16:05:22.188 IST
IS-IS 1 (Level-2) Link State Database
LSPID LSP Seq Num LSP Checksum LSP Holdtime/Rcvd ATT/P/OL
RouterR2.00-00 0x0000004c 0xd97e 773 /1200 0/0/0
Area Address: 49.0000
IPv4 Algo Prefix: MT (Standard (IPv4 Unicast)) 2.2.2.31/32 D:0 Metric: 0 Algorithm: 131
Prefix Attribute Flags: X:0 R:0 N:0 E:0 A:0
Source Router ID: 2.2.2.2
IPv4 Algo Prefix: MT (Standard (IPv4 Unicast)) 2.2.2.51/32 D:0 Metric: 0 Algorithm: 151
Prefix Attribute Flags: X:0 R:0 N:0 E:0 A:0
Source Router ID: 2.2.2.2
IPv4 Algo Prefix: MT (Standard (IPv4 Unicast)) 200.3.1.0/24 D:0 Metric: 10 Algorithm: 131
Prefix Attribute Flags: X:0 R:0 N:0 E:0 A:0
IPv4 Algo Prefix: MT (Standard (IPv4 Unicast)) 200.3.2.0/24 D:0 Metric: 10 Algorithm: 151
Prefix Attribute Flags: X:0 R:0 N:0 E:0 A:0
IPv6 Algo Prefix: MT (IPv6 Unicast) 2:2:2::31/128 D:0 Metric: 0 Algorithm: 131
Prefix Attribute Flags: X:0 R:0 N:0 E:0 A:0
IPv6 Algo Prefix: MT (IPv6 Unicast) 2:2:2::51/128 D:0 Metric: 0 Algorithm: 151
Prefix Attribute Flags: X:0 R:0 N:0 E:0 A:0
NLPID: 0xcc
NLPID: 0x8e
IP Address: 2.2.2.2
Router ID: 2.2.2.2
Metric: 0 IP-Extended 2.2.2.2/32
Prefix-SID Index: 2, Algorithm:0, R:0 N:1 P:0 E:0 V:0 L:0
Prefix-SID Index: 102, Algorithm:131, R:0 N:1 P:0 E:0 V:0 L:0
Prefix Attribute Flags: X:0 R:0 N:1 E:0 A:0
Source Router ID: 2.2.2.2
Metric: 0 MT (IPv6 Unicast) IPv6 2:2:2::2/128
Prefix-SID Index: 12, Algorithm:0, R:0 N:1 P:0 E:0 V:0 L:0
Prefix-SID Index: 112, Algorithm:131, R:0 N:1 P:0 E:0 V:0 L:0
This example verifies Flexible Algorithm 151 is present in only the topology—IP data-plane
RP/0/RP0/CPU0:RouterR1# show isis topology flex-algo 151 data-plane segment-routing
Mon Nov 15 16:20:23.553 IST
IS-IS 1 paths to IPv4 Unicast (Level-2) routers
System Id Metric Next-Hop Interface SNPA
RouterR1 --
RouterR2 **
RouterR3 **
RouterR4 **
RouterR5 **
RouterR6 **
RP/0/RP0/CPU0:RouterR1# show isis topology flex-algo 151 data-plane ip
Mon Nov 15 16:20:30.097 IST
IS-IS 1 paths to IPv4 Unicast (Level-2) routers
System Id Metric Next-Hop Interface SNPA
RouterR1 --
RouterR2 32 RouterR3 Te0/0/0/14.2 *PtoP*
RouterR3 20 RouterR3 BE1 *PtoP*
RouterR4 30 RouterR3 BE1 *PtoP*
RouterR5 ** RouterR5 Te0/0/0/14.2 *PtoP*
RouterR6 ** RouterR5 Te0/0/0/14.2 *PtoP*
These examples verifies the flexible Algorithm 151 IP data-plane IP route.
RP/0/RP0/CPU0:RouterR3# show isis route flex-algo 151 2.2.2.51/32 detail
Mon Nov 15 16:01:50.553 IST
L2 2.2.2.51/32 [32/115] Label: None, medium priority
Installed Nov 15 12:57:39.377 for 03:04:11
via 32.1.15.2, TenGigE0/0/0/14.2, RouterR4, SRGB Base: 17000, Weight: 0
src RouterR2.00-00, 2.2.2.2
RP/0/RP0/CPU0:RouterR3# show isis fast-reroute flex-algo 151 2.2.2.51/32 detail
Mon Nov 15 16:02:04.619 IST
L2 2.2.2.51/32 [32/115] Label: None, medium priority
Installed Nov 15 12:57:39.377 for 03:04:25
via 32.1.15.2, TenGigE0/0/0/14.2, RouterR4, SRGB Base: 17000, Weight: 0
Backup path: LFA, via 32.1.13.2, Bundle-Ether1, RouterR2, SRGB Base: 17000, Weight: 0, Metric: 40
P: No, TM: 40, LC: No, NP: Yes, D: Yes, SRLG: No
src RouterR2.00-00, 2.2.2.2
RP/0/RP0/CPU0:RouterR3# show isis ipv6 route flex-algo 151 2:2:2::51/128 detail
Mon Nov 15 16:02:50.749 IST
L2 2:2:2::51/128 [32/115] Label: None, medium priority
Installed Nov 15 15:45:17.416 for 00:17:33
via fe80::28a:96ff:fee7:f400, TenGigE0/0/0/14.2, RouterR4, SRGB Base: 17000, Weight: 0
src RouterR2.00-00, 2:2:2::2
RP/0/RP0/CPU0:RouterR3# show isis ipv6 fast-reroute flex-algo 151 2:2:2::51/128 detail
Mon Nov 15 16:03:02.722 IST
L2 2:2:2::51/128 [32/115] Label: None, medium priority
Installed Nov 15 15:45:17.416 for 00:17:45
via fe80::28a:96ff:fee7:f400, TenGigE0/0/0/14.2, RouterR4, SRGB Base: 17000, Weight: 0
Backup path: LFA, via fe80::2bc:60ff:fe04:74dc, Bundle-Ether1, RouterR2, SRGB Base: 17000, Weight: 0, Metric: 40
P: No, TM: 40, LC: No, NP: Yes, D: Yes, SRLG: No
src RouterR2.00-00, 2:2:2::2
Topology-Independent Loop-Free Alternate (TI-LFA) and Microloop avoidance features provide protection to link, node, and Shared Risk Link Groups (SRLG) using Segment Routing.
The IP Flexible Algorithm does not support TI-LFA and Microloop avoidance on its own. However, you can protect the IP Algorithm prefixes in the IP network by enabling Segment Routing in the network. With Segment Routing Flexible Algorithm, you can also protect the IP Flexible Algorithm traffic on its backup path.
Following conditions are required for TI-LFA protection and/or Microloop avoidance of the IP Flexible Algorithm traffic:
Both Segment Routing and IP Flexible Algorithms data-planes must be enabled for a particular Flexible Algorithm X in an IS-IS area.
The exact same set of reachable routers in the IS-IS area is participating in the Segment Routing and IP data-planes for Flexible Algorithm X.
The following figure is a six-node topology from R1 to R6 with configurations.
Node R2 is winning the FAD.
IP Flexible Algorithm with Flexible Algorithm 151 on nodes R2 ►R4 ► R3 ►R1.
Segment Routing Flexible Algorithm with Flexible Algorithm 131 on nodes R2 ►R6 ► R5► R1 ► R3 ► R4.
Both Segment Routing and IP Algorithm with Flexible Algorithm 131 on node R1 ► R3 ►R4 ►R2.
This example shows the Flexible Algorithm 131 and 151 configuration on R2.
RP/0/RSP0/CPU0:RouterR2# show run router isis
router isis 1
is-type level-2-only
net 49.0000.0000.0000.0012.00
affinity-map GREEN bit-position 4
flex-algo 131
data-plane segment-routing ip
metric-type delay
advertise-definition
affinity include-any GREEN
!
flex-algo 151
data-plane ip
metric-type delay
advertise-definition
affinity include-any RED
!
address-family ipv4 unicast
metric-style wide
segment-routing mpls sr-prefer
segment-routing mpls unlabeled protection route-policy ip_fa
!
address-family ipv6 unicast
metric-style wide
segment-routing mpls sr-prefer
segment-routing mpls unlabeled protection route-policy ip_fa
interface Loopback0
passive
address-family ipv4 unicast
prefix-sid index 2
prefix-sid algorithm 131 index 102
!
address-family ipv6 unicast
prefix-sid index 12
prefix-sid algorithm 131 index 112
!
!
interface Loopback31
passive
address-family ipv4 unicast
!
address-family ipv6 unicast
!
!
interface Loopback32
passive
address-family ipv4 unicast
!
address-family ipv6 unicast
!
This example shows the Loopback interfaces 31 and 51 associated to Flexible Algorithms 131 and 151 respectively.
RP/0/RSP0/CPU0:RouterR2# show run int Loopback 31
Mon Nov 15 14:02:03.386 IST
interface Loopback31
ipv4 address 2.2.2.31 255.255.255.255 algorithm 131
ipv6 address 2:2:2::31/128 algorithm 131
!
RP/0/RSP0/CPU0:Router# show run int Loopback 51
Mon Nov 15 14:02:09.832 IST
interface Loopback51
ipv4 address 2.2.2.51 255.255.255.255 algorithm 151
ipv6 address 2:2:2::51/128 algorithm 151
!
This example shows the 100-Gigabit Ethernet interface associated to the Flexible Algorithms 131 and 151.
RP/0/RSP0/CPU0:Router# show run int HundredGigE 0/1/0/0.301
Mon Nov 15 14:02:38.800 IST
interface HundredGigE0/1/0/0.301
ipv4 address 200.3.1.1 255.255.255.0 algorithm 131
ipv4 address 200.3.2.1 255.255.255.0 secondary algorithm 151
ipv6 address 200::3:1:1/112 algorithm 131
ipv6 address 200::3:2:1/112 algorithm 151
encapsulation dot1q 301
Use the show isis flex-algo command to verify Flexible Algorithm configurations.
This example verifies Flexible Algorithm 131 configuration on both Segment Routing and IP data-planes.
RP/0/RSP0/CPU0:RouterR2# show isis flex-algo 131
Mon Nov 15 15:54:01.104 IST
IS-IS 1 Flex-Algo Database
Flex-Algo 131:
Level-2:
Definition Priority: 128
Definition Source: Router.00, (Local)
Definition Equal to Local: Yes
Definition Metric Type: Delay
Definition Flex-Algo Prefix Metric: No
Exclude Any Affinity Bit Positions:
Include Any Affinity Bit Positions: 4
Include All Affinity Bit Positions:
Exclude SRLGs:
Disabled: No
Local Priority: 128
FRR Disabled: No
Microloop Avoidance Disabled: No
Data Plane Segemnt Routing: Yes
Data Plane IP: Yes
This example verifies the Flexible Algorithm 151 configuration on the IP data-plane.
RP/0/RSP0/CPU0:RouterR2# show isis flex-algo 151
Mon Nov 15 15:54:06.291 IST
IS-IS 1 Flex-Algo Database
Flex-Algo 151:
Level-2:
Definition Priority: 128
Definition Source: Router.00, (Local)
Definition Equal to Local: Yes
Definition Metric Type: Delay
Definition Flex-Algo Prefix Metric: No
Exclude Any Affinity Bit Positions:
Include Any Affinity Bit Positions: 4
Include All Affinity Bit Positions:
Exclude SRLGs:
Disabled: No
Local Priority: 128
FRR Disabled: No
Microloop Avoidance Disabled: No
Data Plane Segemnt Routing: No
Data Plane IP: Yes
This example verifies the Loopback interface 32 configuration.
RP/0/RSP0/CPU0:RouterR2#show isis interface Loopback 31 VERIFY ALGO AND IP IN ISIS INTERFACE
Mon Nov 15 16:42:30.819 IST
Loopback31 Enabled
Adjacency Formation: Disabled (Passive in IS-IS cfg)
Prefix Advertisement: Enabled
!
IPv4 Address Family: Enabled
Protocol State: Up
Forwarding Address(es): Unknown (Intf passive in IS-IS cfg)
Global Prefix(es): 2.2.2.31/32 (131)
IPv6 Address Family: Enabled
Protocol State: Up
Forwarding Address(es): Unknown (Intf passive in IS-IS cfg)
Global Prefix(es): 2:2:2::31/128 (131)
!
This example verifies the IP Algo Prefix Advertisements in ISIS database on R2.
RP/0/RP0/CPU0:RouterR1# show isis database detail verbose RouterR2
Mon Nov 15 16:05:22.188 IST
IS-IS 1 (Level-2) Link State Database
LSPID LSP Seq Num LSP Checksum LSP Holdtime/Rcvd ATT/P/OL
RouterR2.00-00 0x0000004c 0xd97e 773 /1200 0/0/0
Area Address: 49.0000
IPv4 Algo Prefix: MT (Standard (IPv4 Unicast)) 2.2.2.31/32 D:0 Metric: 0 Algorithm: 131
Prefix Attribute Flags: X:0 R:0 N:0 E:0 A:0
Source Router ID: 2.2.2.2
IPv4 Algo Prefix: MT (Standard (IPv4 Unicast)) 2.2.2.51/32 D:0 Metric: 0 Algorithm: 151
Prefix Attribute Flags: X:0 R:0 N:0 E:0 A:0
Source Router ID: 2.2.2.2
IPv4 Algo Prefix: MT (Standard (IPv4 Unicast)) 200.3.1.0/24 D:0 Metric: 10 Algorithm: 131
Prefix Attribute Flags: X:0 R:0 N:0 E:0 A:0
IPv4 Algo Prefix: MT (Standard (IPv4 Unicast)) 200.3.2.0/24 D:0 Metric: 10 Algorithm: 151
Prefix Attribute Flags: X:0 R:0 N:0 E:0 A:0
IPv6 Algo Prefix: MT (IPv6 Unicast) 2:2:2::31/128 D:0 Metric: 0 Algorithm: 131
Prefix Attribute Flags: X:0 R:0 N:0 E:0 A:0
IPv6 Algo Prefix: MT (IPv6 Unicast) 2:2:2::51/128 D:0 Metric: 0 Algorithm: 151
Prefix Attribute Flags: X:0 R:0 N:0 E:0 A:0
NLPID: 0xcc
NLPID: 0x8e
IP Address: 2.2.2.2
Router ID: 2.2.2.2
Metric: 0 IP-Extended 2.2.2.2/32
Prefix-SID Index: 2, Algorithm:0, R:0 N:1 P:0 E:0 V:0 L:0
Prefix-SID Index: 102, Algorithm:131, R:0 N:1 P:0 E:0 V:0 L:0
Prefix Attribute Flags: X:0 R:0 N:1 E:0 A:0
Source Router ID: 2.2.2.2
Metric: 0 MT (IPv6 Unicast) IPv6 2:2:2::2/128
Prefix-SID Index: 12, Algorithm:0, R:0 N:1 P:0 E:0 V:0 L:0
Prefix-SID Index: 112, Algorithm:131, R:0 N:1 P:0 E:0 V:0 L:0
This example verifies the Flexible Algorithm participation in Segment Routing and IP data-plane in IS-IS database on R2.
RP/0/RP0/CPU0:RouterR1# show isis database detail verbose RouterR2
Mon Nov 15 16:05:22.188 IST
Router Cap: 2.2.2.2 D:0 S:0
Segment Routing: I:1 V:1, SRGB Base: 17000 Range: 7000
SR Local Block: Base: 15000 Range: 1000
Node Maximum SID Depth:
Label Imposition: 10
SR Algorithm:
Algorithm: 0
Algorithm: 131
IP Algorithm:
Algorithm: 131
Algorithm: 151
Flex-Algo Definition:
Algorithm: 131 Metric-Type: 1 Alg-type: 0 Priority: 128
Flex-Algo Include-Any Ext Admin Group:
0x00000010
Flex-Algo Definition:
Algorithm: 151 Metric-Type: 1 Alg-type: 0 Priority: 128
Flex-Algo Include-Any Ext Admin Group:
0x00000010
This exanple verifies Flexible Algorithm 131 is present in both topologies—Segment Routing and IP data-plane
RP/0/RP0/CPU0:RouterR1# show isis topology flex-algo 131 data-plane segment-routing
Mon Nov 15 16:20:05.271 IST
IS-IS 1 paths to IPv4 Unicast (Level-2) routers
System Id Metric Next-Hop Interface SNPA
RouterR1 --
RouterR2 32 RouterR5 Te0/0/0/14.2 *PtoP*
RouterR3 20 RouterR3 BE1 *PtoP*
RouterR4 30 RouterR3 BE1 *PtoP*
RouterR5 12 RouterR5 Te0/0/0/14.2 *PtoP*
RouterR6 22 RouterR5 Te0/0/0/14.2 *PtoP*
RP/0/RP0/CPU0:RouterR1# show isis topology flex-algo 131 data-plane ip
Mon Nov 15 16:20:14.015 IST
IS-IS 1 paths to IPv4 Unicast (Level-2) routers
System Id Metric Next-Hop Interface SNPA
RouterR1 --
RouterR2 32 RouterR5 Te0/0/0/14.2 *PtoP*
RouterR3 20 RouterR3 BE1 *PtoP*
RouterR4 30 RouterR3 BE1 *PtoP*
RouterR5 12 RouterR5 Te0/0/0/14.2 *PtoP*
RouterR6 22 RouterR5 Te0/0/0/14.2 *PtoP*
This example shows Segment Routing Flexible Algorithm 131 prefix with Prefix SIDs.
RP/0/RSP0/CPU0:RouterR2# show isis route flex-algo 131 1.1.1.1/32 detail SR FA 131 PREFIX WITH PREFIX-SID
Mon Nov 15 15:32:53.170 IST
L2 1.1.1.1/32 [31/115] Label: 17101, medium priority
Installed Nov 15 13:46:40.902 for 01:46:13
via 32.1.24.2, TenGigE0/1/0/3/6, Label: 17101, RouterR4, SRGB Base: 17000, Weight: 0
src RouterR1.00-00, 1.1.1.1, prefix-SID index 101, R:0 N:1 P:0 E:0 V:0 L:0, Alg:131
RP/0/RSP0/CPU0:Router#
RP/0/RSP0/CPU0:Router2# show isis fast-reroute flex-algo 131 1.1.1.1/32 detail
Mon Nov 15 15:32:58.794 IST
L2 1.1.1.1/32 [31/115] Label: 17101, medium priority
Installed Nov 15 13:46:40.902 for 01:46:19
via 32.1.24.2, TenGigE0/1/0/3/6, Label: 17101, RouterR4, SRGB Base: 17000, Weight: 0
Backup path: TI-LFA (link), via 32.1.26.2, TenGigE0/1/0/3/5.2 tb5-r6, SRGB Base: 17000, Weight: 0, Metric: 120
P node: RouterR6.00 [6.6.6.6], Label: ImpNull
Q node: RouterR5.00 [5.5.5.5], Label: 25009
Prefix label: 17101
Backup-src: RouterR1.00
P: No, TM: 120, LC: No, NP: No, D: No, SRLG: No
src RouterR1.00-00, 1.1.1.1, prefix-SID index 101, R:0 N:1 P:0 E:0 V:0 L:0, Alg:131
This example shows IP Flexible Algorithm 131 prefix with IP Prefixes.
RP/0/RSP0/CPU0:RouterR2#show isis route flex-algo 131 1.1.1.31/32 detail
Mon Nov 15 15:33:15.970 IST
L2 1.1.1.31/32 [31/115] Label: None, medium priority
Installed Nov 15 13:46:34.923 for 01:46:42
via 32.1.24.2, TenGigE0/1/0/3/6, tb5-r4, SRGB Base: 17000, Weight: 0
src RouterR1.00-00, 1.1.1.1
!!TI-LFA backup is seen only if both IP AND SR TOPOLOGY ARE CONGRUENT
RP/0/RSP0/CPU0:RouterR2#show isis fast-reroute flex-algo 131 1.1.1.31/32 detail
Mon Nov 15 15:33:27.404 IST
L2 1.1.1.31/32 [31/115] Label: None, medium priority
Installed Nov 15 13:46:34.923 for 01:46:54
via 32.1.24.2, TenGigE0/1/0/3/6, tb5-r4, SRGB Base: 17000, Weight: 0
Backup path: TI-LFA (link), via 32.1.26.2, TenGigE0/1/0/3/5.2 tb5-r6, SRGB Base: 17000, Weight: 0, Metric: 120
P node: tb5-r6.00 [6.6.6.6], Label: ImpNull
Q node: tb5-r5.00 [5.5.5.5], Label: 25009
Prefix label: None
Backup-src: RouterR1.00
P: No, TM: 120, LC: No, NP: No, D: No, SRLG: No
src RouterR1.00-00, 1.1.1.1