About the Unicast RIB and FIB
The unicast Routing Information Base (IPv4 RIB and IPv6 RIB) and Forwarding Information Base (FIB) are part of the Cisco NX-OS forwarding architecture, as shown in the following figure.
The unicast RIB exists on the active supervisor. It maintains the routing table with directly connected routes, static routes, and routes learned from dynamic unicast routing protocols. The unicast RIB also collects adjacency information from sources such as the Address Resolution Protocol (ARP). The unicast RIB determines the best next hop for a given route and populates the unicast forwarding information bases (FIBs) on the modules by using the services of the unicast FIB distribution module (FDM).
Each dynamic routing protocol must update the unicast RIB for any route that has timed out. The unicast RIB then deletes that route and recalculates the best next hop for that route (if an alternate path is available).
Layer 3 Consistency Checker
In rare instances, an inconsistency can occur between the unicast RIB and the FIB on each module. Cisco NX-OS supports the Layer 3 consistency checker. This feature detects inconsistencies between the unicast IPv4 RIB on the supervisor module and the FIB on each interface module. Inconsistencies include the following:
Wrong next-hop address
Incorrect Layer 2 rewrite string in the ARP or neighbor discovery (ND) cache
The Layer 3 consistency checker compares the FIB entries to the latest adjacency information from the Adjacency Manager (AM) and logs any inconsistencies. The consistency checker then compares the unicast RIB prefixes to the module FIB and logs any inconsistencies. See the Triggering the Layer 3 Consistency Checker section.
You can then manually clear any inconsistencies. See the Clearing Forwarding Information in the FIB section.
When the consistency checker is run before there is no consistency, consistency passes. But when more routes are learned exceeding the hardware limit of 4K and the show consistency-checker forwarding ipv4 command is run, consistency passes. The same is true when it is transitioning from an inconsistent state to a consistent state. It still shows failure routes. Until and unless the test forwarding ipv4 inconsistency route command is run again, it doesn't leave this state. This is an expected behavior.