Configure Topology-Independent Loop-Free Alternate (TI-LFA)

Topology-Independent Loop-Free Alternate (TI-LFA) uses segment routing to provide link protection in topologies where other fast reroute techniques cannot provide protection. The goal of TI-LFA is to reduce the packet loss that results while routers converge after a topology change due to a link failure. Rapid failure repair (< 50 msec) is achieved through the use of pre-calculated backup paths that are loop-free and safe to use until the distributed network convergence process is completed.


Note
TI-LFA supports IPv4 only.

TI-LFA provides link protection. The link is excluded during the post convergence backup path calculation.

Configuring TI-LFA for IS-IS

This task describes how to enable per-prefix Topology Independent Loop-Free Alternate (TI-LFA) computation to converge traffic flows around link failures.

Before you begin

Ensure that the following topology requirements are met:

  • Router interfaces are configured as per the topology.

  • Routers are configured with IS-IS.

  • Segment routing for IS-IS is configured. See Enabling Segment Routing for IS-IS Protocol.

  • Enter the following commands in global configuration mode:

    Router(config)# ipv4 unnumbered mpls traffic-eng Loopback0
Router(config)# mpls traffic-eng
Router(config-mpls-te)# exit
Router(config)#

SUMMARY STEPS

  1. configure
  2. router isis instance-id
  3. interface type interface-path-id
  4. address-family ipv4 [ unicast]
  5. fast-reroute per-prefix
  6. fast-reroute per-prefix ti-lfa

DETAILED STEPS

  Command or Action Purpose
Step 1

configure

Step 2

router isis instance-id

Example:


RP/0/RP0/CPU0:router(config)# router isis 1

Enables IS-IS routing for the specified routing instance, and places the router in router configuration mode.

Note 
You can change the level of routing to be performed by a particular routing instance by using the is-type router configuration command.
Step 3

interface type interface-path-id

Example:


RP/0/RP0/CPU0:router(config-isis)# interface GigabitEthernet0/0/2/1

Enters interface configuration mode.
Step 4

address-family ipv4 [ unicast]

Example:


RP/0/RP0/CPU0:router(config-isis-if)# address-family ipv4 unicast

Specifies the IPv4 address family, and enters router address family configuration mode.

Step 5

fast-reroute per-prefix

Example:


RP/0/RP0/CPU0:router(config-isis-if-af)# fast-reroute per-prefix

Enables per-prefix fast reroute .

Step 6

fast-reroute per-prefix ti-lfa

Example:


RP/0/RP0/CPU0:router(config-isis-if-af)# fast-reroute per-prefix ti-lfa

Enables per-prefix TI-LFA fast reroute link protection.

TI-LFA has been successfully configured for segment routing.

Configuring TI-LFA for OSPF

This task describes how to enable per-prefix Topology Independent Loop-Free Alternate (TI-LFA) computation to converge traffic flows around link failures.


Note
TI-LFA can be configured on the instance, area, or interface. When configured on the instance or area, all interfaces in the instance or area inherit the configuration.

Before you begin

Ensure that the following topology requirements are met:

  • Router interfaces are configured as per the topology.

  • Routers are configured with OSPF.

  • Segment routing for OSPF is configured. See Enabling Segment Routing for OSPF Protocol.

  • Enter the following commands in global configuration mode:

    Router(config)# ipv4 unnumbered mpls traffic-eng Loopback0
Router(config)# mpls traffic-eng
Router(config-mpls-te)# exit
Router(config)#

SUMMARY STEPS

  1. configure
  2. router ospf process-name
  3. area area-id
  4. interface type interface-path-id
  5. fast-reroute per-prefix
  6. fast-reroute per-prefix ti-lfa

DETAILED STEPS

  Command or Action Purpose
Step 1

configure

Step 2

router ospf process-name

Example:


RP/0/RP0/CPU0:router(config)# router ospf 1

Enables OSPF routing for the specified routing process, and places the router in router configuration mode.

Step 3

area area-id

Example:


RP/0/RP0/CPU0:router(config-ospf)# area 1

Enters area configuration mode.

Step 4

interface type interface-path-id

Example:


RP/0/RP0/CPU0:router(config-ospf-ar)# interface GigabitEthernet0/0/2/1

Enters interface configuration mode.
Step 5

fast-reroute per-prefix

Example:


RP/0/RP0/CPU0:router(config-ospf-ar-if)# fast-reroute per-prefix

Enables per-prefix fast reroute.

Step 6

fast-reroute per-prefix ti-lfa

Example:


RP/0/RP0/CPU0:router(config-ospf-ar-if)# fast-reroute per-prefix ti-lfa

Enables per-prefix TI-LFA fast reroute link protection.

TI-LFA has been successfully configured for segment routing.