BFD for BGP
BGP periodically sends messages to peers to detect the status of the peers. It takes more than 1 second for this detection mechanism to detect a fault. When data is transmitted at gigabit rates, long-time fault detection will cause packet loss. This cannot meet high reliability requirements of networks. Bidirectional Forwarding Detection (BFD) provides the millisecond-level fault detection for BGP to improve network reliability.
As shown in Figure 1, RouterA belongs to AS 100 and RouterB belongs to AS 200. RouterA and RouterB are directly connected and establish the EBGP peer relationship. Association between BGP and BFD is configured on RouterA and RouterB. When a fault occurs on the link between RouterA and RouterB, BFD can rapidly detect that the BFD session changes from Up to Down and notify this fault to RouterA and RouterB. RouterA and RouterB process the neighbor Down event and select routes again using BGP.