This article describes scenarios in which BGP neighbors may miss updates from their peers.

In some scenarios, BGP peers may experience discrepancies in BGP updates. They could either observe delays in the updates or miss them entirely if one of the peers flaps within the same peer group.

In some scenarios, when one peer in the BGP group (e.g., JUNIPER_TEST, which includes the affected peer 10.10.10.1) was stable, while another peer, 20.20.20.1, in the same group, was continuously flapping, updates to the stable peer were halted whenever the flapping peer came back online. However, when the flapping peer went down, updates resumed.

It appears that when a peer keeps flapping within the same group, the regular updates to the stable peers are delayed until the Route Reflector (RR) is able to synchronize all required routes with the flapping peer. Essentially, the RR seems to be aligning the route advertisements between the flapping peer and stable peers before resuming regular updates to all peers in the group.

Since update messages are sent on a per-group basis, whenever a peer flaps multiple times in the group, the RR pauses updates for the rest of the group. This behavior has been confirmed with engineering and is considered expected.