Routing Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

PDF

Routing Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

Fast reroute with remote loop-free alternate

Updated: June 30, 2026

Want to summarize with AI?

Describes how remote LFA tunnels traffic to a precomputed backup node more than one hop away to minimize loss during failures and speed recovery.

The fast reroute with remote loop-free alternate (FRR Remote LFA) is a resiliency feature that

enables rapid traffic redirection during link or router failures
uses precomputed alternate next hops to bypass failed network segments, and
supports recovery for failures that are more than one hop away from the point of local repair.

Table 1. Feature History Table
Feature Name	Release Information	Feature Description
Fast Reroute with Remote Loop-Free Alternate	Release 25.1.1	Introduced in this release on: Fixed Systems (8010 [ASIC: A100])(select variants only) This feature is supported on Cisco 8011-4G24Y4H-I routers.
Fast Reroute with Remote Loop-Free Alternate	Release 24.4.1	Introduced in this release on: Fixed Systems (8200 [ASIC: P100], 8700 [ASIC: P100, K100])(select variants only); Modular Systems (8800 [LC ASIC: P100])(select variants only) This feature minimizes traffic loss by rerouting packets around failed links quickly. It precomputes repair paths using the IS-IS routing protocol, allowing routers to switch immediately to these paths when a failure occurs, reducing transition time to under 50 milliseconds. This feature is supported on: 8212-48FH-M 8711-32FH-M 8712-MOD-M 88-LC1-36EH 88-LC1-12TH24FH-E 88-LC1-52Y8H-EM

Routing transition and convergence

When a link or router fails, distributed routing protocols must compute new paths. During this routing transition, traffic to affected destinations can be interrupted until the routers converge. Standard IGP or BGP convergence can take several hundred milliseconds. FRR remote LFA reduces this interruption by letting the router switch immediately to a precomputed repair path when it detects the failure.

FRR remote LFA with ring topology

Consider this ring topology for FRR remote LFA.

Device A sends traffic for destination F through next-hop B. Device B cannot serve as a loop-free alternate (LFA) for prefixes that nodes C and F advertise. The actual LFA is node D, but node D is not directly connected to the protecting node, A. To protect prefixes that node C advertises, node A must tunnel the packet around the failed A-to-C link to node D, as long as the tunnel does not use the failed link.

FRR remote LFA lets you tunnel a packet around a failed link to a remote loop-free alternate that is more than one hop away. The feature automatically creates the tunnel to avoid looping.

How FRR remote LFA computes and installs repair paths

FRR remote LFA protects network topologies in which local LFA fast reroute (FRR) does not provide enough coverage, such as ring-based topologies. It lets interior gateway protocols (IGPs) use non-directly connected neighbors as backup paths.

Summary

This process uses these components:

IGP: Identifies a non-directly connected neighbor as the LFA backup path.
Label Distribution Protocol (LDP): Establishes a labeled backup label-switched path (LSP) to the remote next hop and a transport LSP for tunneling.
Cisco Express Forwarding: Installs the repair paths that the routing protocols compute.

Workflow

These stages describe how FRR remote LFA works.

IGP identifies a remote neighbor that is more than one hop away as the LFA backup path.
LDP establishes a labeled backup LSP to the remote next hop.
LDP creates a transport LSP that tunnels traffic to the remote node.
Cisco Express Forwarding installs the repair path so that the router can switch traffic immediately when it detects a link or router failure.

Result

The network can achieve sub-50 millisecond convergence by using a precomputed repair path.

Configure remote FRR with remote LFA using IS-IS

This example shows an IPv4 LFA FRR configuration. IPv6 LFA FRR is also supported.

Procedure

Configure the IS-IS routing process and interfaces for remote LFA.

Example:

Router# configure
Router(config)# router isis ring
Router(config-isis)# is-type level-1
Router(config-isis)# net 49.0001.0000.0000.0007.00
Router(config-isis)# nsf cisco
Router(config-isis)# address-family ipv4 unicast
Router(config-isis-af)# metric-style wide
Router(config-isis-af)# exit
Router(config-isis)# interface Loopback 0
Router(config-isis-if)# point-to-point
Router(config-isis-if)# address-family ipv4 unicast
Router(config-isis-if)# exit
Router(config-isis)# interface TenGigabitEthernet 0/0/0/4
Router(config-isis-if)# point-to-point
Router(config-isis-if)# address-family ipv4 unicast

Enable FRR LFA computation.


If...	Then...
Enable FRR LFA prefix dependent computation	Configure the `fast-reroute per-prefix` command.
Enable FRR LFA prefix independent per-link computation	Configure the `fast-reroute per-link` command.

Example:

Router(config-isis-af)# fast-reroute per-prefix
Router(config-isis-af)# fast-reroute per-prefix remote-lfa tunnel mpls-ldp
Router(config-isis-af)# fast-reroute per-prefix remote-lfa prefix-list
Router(config-isis-af)# commit

Example:

FRR with remote LFA running configuration

router isis ring
 is-type level-1
 net 49.0001.0000.0000.0007.00
 nsf cisco
 address-family ipv4 unicast
 fast-reroute per-prefix remote-lfa prefix-list abc
  metric-style wide
 !
 interface Loopback0
  point-to-point
  address-family ipv4 unicast
 !
 !
 interface TenGigabitEthernet 0/0/0/4
  point-to-point
  address-family ipv4 unicast
   fast-reroute per-prefix remote-lfa prefix-list 
   fast-reroute per-prefix remote-lfa tunnel mpls-ldp

Verify the route summary information about the specified routing table.

Example:

Router# show route 10.3.3.3
Routing entry for 10.3.3.3/32
   Known via "isis 44", distance 115, metric 20, type level-1
   Installed Nov 15 19:43:13.367 for 00:00:34
   Routing Descriptor Blocks
     10.1.1.1, from 10.3.3.3, via TenGigE0/0/0/0, Backup (remote)
       Remote LFA is 10.9.9.9
      Route metric is 0
     10.1.1.2, from 10.3.3.3, via TenGigE0/7/0/3, Protected
       Route metric is 20
   No advertising protos.

Verify the MPLS LDP configuration.

Example:

Router# show running mpls ldp 
Codes:
   - = GR label recovering, (!) = LFA FRR pure backup path
   {} = Label stack with multi-line output for a routing path
   G = GR, S = Stale, R = Remote LFA FRR backup
  
 Prefix           Label   Label(s)       Outgoing     Next Hop            Flags
                  In      Out            Interface                        G S R
 ------------- ----- -------- -------- --------------- ----
 192.0.2.0/24     16019   { 16001        Te0/0/0/0    10.1.1.1        (!)     R
                            28006 }                   (10.9.9.9)
                          ImpNull        Te0/7/0/3    192.0.2.1
 192.0.2.1/32     16013   ImpNull        Te0/0/0/0    10.1.1.1
 192.0.1.0/32     16014   { 16001        Te0/0/0/0    10.1.1.1        (!)     R
                            16002 }                   (10.9.9.9)
                          ImpNull        Te0/7/0/3    192.0.2.2
 10.9.9.9/32      16012   16001          Te0/0/0/0    10.1.1.1
                          28006          Te0/7/0/3    192.0.2.1
 10.23.1.0/24     16018   16004          Te0/0/0/0    10.1.1.1        (!)
                          ImpNull        Te0/7/0/3    192.0.2.1
 10.34.1.0/24     16015   ImpNull        Te0/0/0/0    10.1.1.1
 10.0.0.1/32      16011  { 16001         Te0/0/0/0     10.1.1.1        (!)     R
                            16013 }                   (10.9.9.9)
                          16016          Te0/7/0/3    192.0.2.1
 10.100.0.2/32     16010   { 16001       Te0/0/0/0    10.1.1.1         (!)     R

Configure FRR with remote LFA using OSPF

This example shows an IPv4 LFA FRR configuration. IPv6 LFA FRR is also supported.

Procedure

Enter configuration mode.

Example:

Router# configure

Enter OSPF configuration mode and specify the process ID.

Example:

Router(config)# router ospf 50
Router(config-ospf)# router-id 10.1.1.1

Enter address-family configuration mode.

Example:

Router(config-ospf)# address-family ipv4 unicast
Router(config-ospf-af)# area 0

Configure the interface for OSPF.

Example:

Router(config-ospf-af)# interface Loopback 0
Router(config-ospf-af)# exit

Configure the interface for FRR LFA.


If...	Then...
Enable FRR LFA prefix dependent computation	Use the fast-reroute per-prefix command.
Enable FRR LFA prefix independent per-link computation	Use the fast-reroute per-link command.

Example:

Router(config-ospf)# interface HundredGigE0/2/0/0
Router(config-ospf-if)# fast-reroute per-prefix remote-lfa tunnel mpls-ldp
Router(config-ospf-if)# commit

Example:

IPv4 LFA FRR running configuration

router ospf 50
 router-id 10.1.1.1
address-family ipv4 unicast
 area 0
   interface Loopback0
  !
  interface HundredGigE 0/2/0/0
    fast-reroute per-prefix remote-lfa tunnel mpls-ldp
  !
!

Need help?

Open a support case

(Requires a Cisco Service Contract)

The documentation set for this product strives to use bias-free language. For the purposes of this documentation set, bias-free is defined as language that does not imply discrimination based on age, disability, gender, racial identity, ethnic identity, sexual orientation, socioeconomic status, and intersectionality. Exceptions may be present in the documentation due to language that is hardcoded in the user interfaces of the product software, language used based on RFP documentation, or language that is used by a referenced third-party product. Learn more about how Cisco is using Inclusive Language.