iBGP Fall-over Trick
BGP fall-over is a neat BGP convergence optimisation technique whereby BGP peering is brought down as soon as the route to neighbor disappears from a routing table.
The difference between external and internal BGP is that the former usually peers over a directly-attached interface so that when the interface to neighbor is disconnected,
route is withdrawn from the routing table which triggers eBGP fall-over to bring down the neighborship.
iBGP, on the other hand, normally uses device loopbacks to establish peering sessions. What this means is if a summary or a default route is present in the routing table (either static or learned
via IGP), there is always a route to iBGP neighbor. In this case BGP has to wait for default 180 seconds (3 x keepalive timer) to bring down the neighborship and withdraw all the routes learned from dead neighbor.
To overcome that there’s a route-map option for a neighbor fall-over command which allows user to specify the exact prefix for which to look in the routing table. In the example below, the router will
look for specific host routes representing neighbor’s loopbacks and will trigger reconvergence as soon as those routes disappear.
Visibility is the first step toward data center security, vArmour reasons.
