BFD – Bidirectional Forwarding Detection
1. What is BFD?
BFD stands for Bidirectional Forwarding Detection and it’s a protocol that is used for rapid detection of link failures when the line-protocol is still “up”. BFD is enabled on interface and creates a BFD session with the neighboring router (BFD Peer). Routing protocols such as EIGRP, OSPF and BGP support BFD and can rapidly detect a link failure without waiting for hold-timers to expire.
2. Enabling BFD
To enable BFD per interface, use:
R(config)# interface INTERFACE R(config-if)# bfd interval TX-MSEC min_rx RX-MSEC multiplier COUNT ! TX-MSEC = rate at which BFD packets are sent ! RX-MSEC = Min rate at which BFD packets are expected ! COUNT = how many packets can be missed before considering the link down
To verify BFD, use:
R# show bfd neighbors [detail]
2. BFD Support for routing protocols
2.1 EIGRP
To enable BFD support for EIGRP, use:
R(config)# router eigrp AS-NUMBER R(config-router)# bfd {interface INTERFACE|all-interfaces}
To verify, use:
R# show ip eigrp interfaces ... [details]
2.2 OSPF
To enable BFD support for OSPF, there are 2 options:
Option 1 is to enable OSPF support for BFD, one-by-one on each interface:
R(config)# interface INTERFACE R(config-if)# ip ospf bfd
Option 2 is to enable OSPF support for all BFD interfaces and the disable it on unneeded interfaces:
R(config)# router ospf PROC-ID R(config-router)# bfd all-interfaces ! Will enable BFD support for all interfaces
You can disable then OSPF support for BFD, per-interface, with:
R(config-if)# ip ospf bfd disable
To verify, use:
R# show ip ospf [details]
2.3 BGP
To enable BFD support for BGP, use:
R(config)# router bgp AS-NUMBER R(config-router)# neighbor NEIGH-IP fall-over bfd
To verify, use:
R# show ip bgp neighbors
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