This document describes the syslog message %IPRT-3-RIB_LOOP: Resolution loop formed by routes in RIB.
The syslog message %IPRT-3-RIB_LOOP: Resolution loop formed by routes in RIB means that a routing loop was introduced into the Routing Information Table (RIB), the routing table of the router when it resolves routes. The cause of this could be a change in the network topology (for example, an interface flap), a normal temporary routing convergence event, or a misconfiguration.
If the error is temporary/transient, this might be perfectly normal during a routing convergence. If this is persistent, it needs investigation.
An example of how a routing loop can be formed due to bad configuration and operation is explained in show ip route loops.
Complete these steps:
Enter the show ip route loops command in order to identify which routes are involved and how the loop occurred.
Check what recent changes were made to the network and/or routing protocols.
Try to correct the misconfiguration, if any.
Check for possible known defects with loops in the RIB for the specific Cisco IOS® version.
Check for side effects, such as continuous high CPU and route churn in the RIB.