Description

This article clarifies that the Bidirectional Forwarding Detection (BFD) feature will not work on Abstracted Fabric (AF) interfaces in MX Series routers where node slicing is deployed because BFD is not supported in such a scenario. 

Symptoms

When you configure the Bidirectional Forwarding Detection (BFD) feature on Abstracted Fabric (AF) interfaces, you will see that a BFD error is logged and that the feature does not work as expected. For example: 

MX> show configuration protocols ospf | display inheritance no-comments
Apr 28 11:52:41
traffic-engineering {
    shortcuts;
}
area 0.0.0.0 {
    interface fxp0.0 {
        disable;
    }
    interface fxp1.0 {
        disable;
    }
    interface lo0.0 {
        passive;
    }
    interface af0.10 {
        interface-type p2p;
        metric 120;
        bfd-liveness-detection {
            minimum-interval 300;
            multiplier 3;
            authentication {
                key-chain BFD-MD5;
                algorithm keyed-md5;
            }
        }
    }
    interface af0.20 {
        interface-type p2p;
        metric 120;
        bfd-liveness-detection {
            minimum-interval 300;
            multiplier 3;
            authentication {
                key-chain BFD-MD5;
                algorithm keyed-md5;
            }
        }                              
    }
}

MX> show ospf neighbor detail             
Apr 28 11:52:25
Address          Interface              State           ID               Pri  Dead
203.208.10.1     af0.10                 Full            202.160.242.200  128    38
  Area 0.0.0.0, opt 0x52, DR 0.0.0.0, BDR 0.0.0.0
  Up 01:34:12, adjacent 01:34:12
203.208.20.1     af0.20                 Full            202.160.242.200  128    35
  Area 0.0.0.0, opt 0x52, DR 0.0.0.0, BDR 0.0.0.0
  Up 00:00:51, adjacent 00:00:51

MX> show log ospf-trace.log | match bfd   
Apr 28 11:50:04.112512 Strict BFD: NOT SUPPORTED by neighbor 203.208.20.1
Apr 28 11:50:04.113441 Strict BFD: NOT SUPPORTED by neighbor 203.208.20.1
Apr 28 11:50:04.216397 Strict BFD: NOT SUPPORTED by neighbor 203.208.20.1
Apr 28 11:50:09.129077 Strict BFD: BFD UP notification received for neighbor 203.208.20.1 over interface af0.20
Apr 28 11:51:34.585866 OSPF neighbor 203.208.20.1 (realm ospf-v2 af0.20 area 0.0.0.0) state changed from Full to Down due to InActiveTimer (event reason: BFD session timed out and neighbor was declared dead) (nbr helped: 0)
Apr 28 11:51:34.585917 RPD_OSPF_NBRDOWN: OSPF neighbor 203.208.20.1 (realm ospf-v2 af0.20 area 0.0.0.0) state changed from Full to Down due to InActiveTimer (event reason: BFD session timed out and neighbor was declared dead)
Apr 28 11:51:34.591958 Strict BFD: NOT SUPPORTED by neighbor 203.208.20.1
Apr 28 11:51:34.594100 Strict BFD: NOT SUPPORTED by neighbor 203.208.20.1
Apr 28 11:51:36.266543 Strict BFD: BFD UP notification received for neighbor 203.208.20.1 over interface af0.20
 

Solution

When you deploy node slicing on MX routers, AF interfaces do not support the BFD feature.