BGP Tracking
BGP tracking provides fast link fault detection to speed up network convergence. When a fault occurs on the link between BGP peers that have BGP tracking configured, BGP tracking can quickly detect peer unreachability and instruct the routing management module to notify BGP of the fault, achieving rapid network convergence.
Compared to BFD, BGP tracking is easy to configure because it needs to be configured only on the local device. BGP tracking is a fault detection mechanism at the routing layer, whereas BFD is a fault detection mechanism at the link layer. BGP route convergence on a network where BGP tracking is configured is slower than that on a network where BFD is configured. Therefore, BGP tracking is not suitable for voice services that require fast convergence.
Applications
In Figure 1, RouterA and RouterB, and RouterB and RouterC establish IGP connections. RouterA and RouterC establish an IBGP peer relationship. BGP tracking is configured on RouterA. When a fault occurs on the link between RouterA and RouterB, IGP performs fast convergence. Subsequently, BGP tracking detects the unreachability of the route to RouterC and notifies the fault to BGP on RouterA, which then interrupts the BGP connection with RouterC.
If establishing an IBGP peer relationship requires IGP routes, the interval between peer unreachability discovery and connection interruption needs to be configured. This interval must be longer than the IGP route convergence time. Otherwise, before IGP route flapping caused by transient interruption is suppressed, the BGP peer relationship may have been interrupted, causing unnecessary BGP convergence.