Concept Guide
For example, the following illustration shows a sample BFD conguration on Router 1 and Router 2 that use eBGP in a transit network to
interconnect AS1 and AS2. The eBGP routers exchange information with each other as well as with iBGP routers to maintain connectivity
and accessibility within each autonomous system.
Figure 15. Establishing Sessions with BGP Neighbors
The sample conguration shows alternative ways to establish a BFD session with a BGP neighbor:
• By establishing BFD sessions with all neighbors discovered by BGP (the bfd all-neighbors command).
• By establishing a BFD session with a specied BGP neighbor (the neighbor {ip-address | peer-group-name} bfd
command)
BFD packets originating from a router are assigned to the highest priority egress queue to minimize transmission delays. Incoming BFD
control packets received from the BGP neighbor are assigned to the highest priority queue within the control plane policing (COPP)
framework to avoid BFD packets drops due to queue congestion.
BFD noties BGP of any failure conditions that it detects on the link. Recovery actions are initiated by BGP.
BFD for BGP is supported only on directly-connected BGP neighbors and in both BGP IPv4 and IPV6 networks. Up to 200 simultaneous
BFD sessions are supported.
As long as each BFD for BGP neighbor receives a BFD control packet within the congured BFD interval for failure detection, the BFD
session remains up and BGP maintains its adjacencies. If a BFD for BGP neighbor does not receive a control packet within the detection
interval, the router informs any clients of the BFD session (other routing protocols) about the failure. It then depends on the individual
routing protocols that uses the BFD link to determine the appropriate response to the failure condition. The typical response is to terminate
the peering session for the routing protocol and reconverge by bypassing the failed neighboring router. A log message is generated
whenever BFD detects a failure condition.
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Bidirectional Forwarding Detection (BFD)