When the FIB table is full, assuming we are talking about hardware assisted platforms, traffic will be forwarded in software. There isn't any wildcard entry for redirection, traffic is simply punted to the CPU.
I respectfully disagree. Several sources on CEF insist that if the TCAM is full, a wildcard entry is installed in the place of all FIB entries that did not make it into the TCAM, and this wildcard entry causes the packets to be processed in software. For example, this is how CCNP Networking Academy curricula put it.
This fact seems to be corroborated also by the following document:
Note: In the rare case in which the FIB table is full, the wildcard entry is still present but, instead of dropping packets that match it, they are forwarded to the MSFC2. This only occurs if you have more than a 256K prefix in the FIB and if you cannot store the complete routing table and ARP adjacency in the FIB. You then need to have the default mechanism sent to MSFC2 since the MSFC2 can have a routing entry that is not present in the FIB.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...