Interfaces and Hardware Component Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

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Interfaces and Hardware Component Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

Configure link loss forwarding for CFM

Updated: September 8, 2026

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This topic describes how to configure LLF on a network by configuring a CFM domain and service, a MEP under the CFM domain and service, the continuity check message (CCM) interval on the MEP, Client Signal Fail (CSF) transmission and logging, and by enabling LLF on an interface.

Use this procedure to configure LLF on a network.

Procedure

  1. Configure a Connectivity Fault Management (CFM) domain and service.

    Example:

    Router# configure
Router(config)# ethernet cfm
Router(config-cfm)# domain dom1 level 1 service ser1 bridge group up-meps bridge-domain up-mep
    The CFM domain and service are established.

  2. Configure a Maintenance End Point (MEP) under the CFM domain and service.

    Example:

    Router(config)# interface GigabitEthernet0/2/0/0
Router(config-if)# ethernet cfm
Router(config-if-cfm)# mep domain dom1 service ser1 mep-id 1
    The MEP is defined under the specified CFM domain and service.

  3. Configure continuity check message (CCM) interval on the MEP. By default, the restore timer for a CCM notification is calculated based on the configured CCM interval.

    Example:

    Router(config-cfm-dmn-svc)# continuity-check interval 1m
    The CCM interval is set on the MEP.

  4. Configure Client Signal Fail (CSF) transmission on the MEP, to enable CSF transmission.

  5. Configure CSF logging on the MEP, to enable logging on receiving a CSF packet.

    Example:

    Router(config-cfm-dmn-svc)# csf interval 1m cos 4
Router(config-cfm-dmn-svc)# csf-logging
    Note

    The CSF configuration is optional and is not required when both the devices in CFM-protected network are running with IOS-XR. This configuration is required for inter-operation with certain client-end setups that contain devices from other clients.

    CSF transmission is enabled and logging is active upon receiving a CSF packet.

  6. Enable LLF on an interface using the propagate-remote-status command. This command triggers the interface to be TX-disabled on fault detection.

    Example:

    Router(config-if-cfm-mep)# propagate-remote-status
Router(config-if-cfm-mep)# commit

  7. Verify the LLF configuration and fault state for each interface

    Example:

    Router# show ethernet cfm interfaces llf location 0/RP0/CPU0
Defects (from at least one peer MEP):
A - AIS received I - Wrong interval
R - Remote Defect received V - Wrong Level
L - Loop (our MAC received) T - Timed out (archived)
C - Config (our ID received) M - Missing (cross-check)
X - Cross-connect (wrong MAID) U - Unexpected (cross-check)
P - Peer port down F – CSF received
GigabitEthernet0/1/0/0
MEP Defects Restore Timer
----- ---------------------------------- --------------
100 R Not running
101 None 10s remaining
102 RPF Not running
GigabitEthernet0/1/0/1
MEP Defects Restore Timer
----- ---------------------------------- --------------
110 None 3s remaining
GigabitEthernet0/1/0/2
MEP Defects Restore Timer
----- ---------------------------------- --------------
120 P 5s Not running

    The following output shows that the interface received a single CSF packet at 1 minute interval, so that the interface is TX-disabled with a damping timer of 3.5 minutes.

    Example:

    Router# show ethernet cfm local meps detail
Domain dom1 (Level 1), Service ser1
UP MEP on GigabitEthernet0/1/0/0 MEP-ID 1
========================================================================================
Interface state: UP MAC address: 0204.3dbe.c93b
Peer MEPs: 0 up, 0 with errors, 0 timed out (archived)
Cross-check errors: 0 missing, 0 unexpected
CCM generation enabled: No
AIS generation enabled: No
Sending AIS: No
Receiving AIS: No
Sending CSF: No
Receiving CSF: Yes (Interval: 1min, started 00:03:29 ago)
TX Disable triggered: Yes (restore timer not running)

    The following output shows that the interface received a CCM notification that the peer MEP port is down, so that the interface is TX-disabled.

    Example:

    Router# show ethernet cfm local meps detail
Domain dom1 (Level 1), Service ser1
UP MEP on GigabitEthernet0/1/0/0 MEP-ID 1
========================================================================================
Interface state: UP MAC address: 0204.3dbe.c93b
Peer MEPs: 1 up, 1 with errors, 0 timed out (archived)
Cross-check errors: 0 missing, 0 unexpected
CCM generation enabled: Yes, 1min (Remote Defect detected: Yes)
CCM defects detected: P - peer port down
AIS generation enabled: No
Sending AIS: No
Receiving AIS: No
Sending CSF: No
Receiving CSF: No
TX Disable triggered: Yes (restore timer 5s not running)

    The following output shows that the interface received CCM notification that the peer MEP port is up, and restore timer is started for the TX-disabled interface.

    Example:

    Router# show ethernet cfm local meps detail
Domain dom1 (Level 1), Service ser1
UP MEP on GigabitEthernet0/1/0/0 MEP-ID 1
========================================================================================
Interface state: UP MAC address: 0204.3dbe.c93b
Peer MEPs: 1 up, 0 with errors, 0 timed out (archived)
Cross-check errors: 0 missing, 0 unexpected
CCM generation enabled: Yes, 1min (Remote Defect detected: No)
AIS generation enabled: No
Sending AIS: No
Receiving AIS: No
Sending CSF: No
Receiving CSF: No
TX Disable triggered: Yes (restore timer running, 1183ms remaining)

    The following output shows Ether-MA configured bundles and their members:

    Example:

    Router# show ethernet infra internal ether-ma bundles
Bundle interface: Bundle-Ether1 (TX disabled)
Bundle members:
GigabitEthernet0/1/0/1
GigabitEthernet0/1/0/2
Bundle interface: Bundle-Ether2
Bundle members:
GigabitEthernet0/2/0/1