With BGP Auto FRR, if a peer has multiple routes with the same prefix that are learned from different peers, the peer uses the optimal route as the primary link to forward packets and the less optimal route as a backup link. If the primary link fails, the peer rapidly notifies other peers that the BGP route has become unreachable and then switches traffic from the primary link to the backup link.
Usage Scenario
On the network shown in Figure 1, Device Y advertises a learned BGP route to Device X2 and Device X3 in AS 100; Device X2 and Device X3 then advertise the BGP route to Device X1 through RR. Therefore, Device X1 receives two routes whose next hops are Device X2 and Device X3 respectively. Then, Device X1 selects a route based on a configured routing policy. Assume that the route sent by Device X2 (Link A) is preferred. The route sent by Device X3 (Link B) then functions as a backup link.
If a node along Link A fails or faults occur on Link A, the next hop of the route from Device X1 to Device X2 becomes unavailable. If BGP Auto FRR is enabled on Device X1, the forwarding plane then quickly switches to Link B the traffic from Device X1 to Device Y, which ensures uninterrupted traffic transmission. In addition, Device X1 reselects the route sent by Device X3 based on the forwarding prefixes and then updates the FIB table.