BGP Soft Reconfiguration RIB Tables

BGP Soft Reconfiguration is one way to dynamically and efficiently request a re-advertisement of prefixes of BGP peers whenever a change in policy is enacted.

Several RIB (Routing Information Base) constructs are vital to understanding how BGP route information is processed and stored. These constructs include the Loc-RIB and the adj-RIB-Out, which are always present in the router, irrespective of the configuration.

To inspect these constructs, network administrators can use the show ip bgp command, optionally appended with the advertised-routes keyword to view advertised routing information.

However, the adj-RIB-In is not inherently present unless soft reconfiguration is enabled on the router. Without this configuration, attempts to view received routes will fail like so:

R1#show ip bgp neighbors 192.168.12.2 received-routes
% Inbound soft reconfiguration not enabled on 192.168.12.2

When soft reconfiguration is activated, the router will allocate additional memory resources to create the adj-RIB-In. This allows for the tracking of all received routes, a process which increases the resource usage of the router due to the additional memory allocation required.

Links

https://networklessons.com/bgp/bgp-soft-reset-reconfiguration/