Setting a Delay in Releasing an Obtained Label in a BGP EVPN FRR Switchover Scenario

Usage Scenario

As shown in Figure 1, Device A and Device D belong to AS100, and Device B, Device C, Device E, and Device F belong to AS200 in a BGP EVPN FRR switchover scenario. Device B selects the optimal route that is learned from the EBGP EVPN peer Device A and the sub-optimal route that is learned from the IBGP EVPN peer Device E. In normal situations, Device B preferentially selects a labeled BGP route learned from EBGP EVPN peer Device A and advertises the route to the IBGP EVPN peer Device C. Device B delivers an incoming label map (ILM) entry and next hop label forwarding entry (NHLFE), and Device C also delivers an NHLFE entry. If Device A is restarted due to a fault, Device B withdraws the route learned from Device A, selects the sub-optimal route learned from IBGP EVPN peer Device E, and reflects the route to Device C through the RR. Then, Device B releases the applied label and deletes the ILM entry mapped to the label. If traffic arrives at Device C before Device C updates the NHLFE entry, Device C still uses this entry to forward traffic to Device B. Because Device B has released the label and deleted the ILM entry, packets are lost for the second time.

Figure 1 Networking for packet loss during a BGP EVPN FRR switchover

To prevent traffic loss during a BGP EVPN FRR switchover, configure the local device to delay deleting the ILM entry.

Pre-configuration Tasks

Before setting a delay in releasing an obtained label in a BGP EVPN FRR switchover scenario, complete the following tasks:

• Configure EVPN or BD EVPN.

• Configure BGP Auto FRR in the BGP-EVPN address family view.