Thursday, December 6, 2012

CEF FIB Table Entries

Cisco Express Forwarding aka CEF is made of two tables called Forwarding Information Base(FIB) and Adjacency table. Every table has its own data structure and passes some kind of information about the destination network.

CEF FIB table has special type of entries as listed below:-
1. Attached FIB entry:- Attached FIB entries are built for destinations which are actually attached to the router and for destinations which are configured via static routes to appear connected to the router e.g. ip route x.y.z.x via an interface.
2. Connected Entry:- A FIB entry is marked as connected entry if it is actually created because of an ip address command on a router’s interface.
3. Receive FIB Entry:- Receive FIB entries are built when the router should receive (process locally) packets destined to the address.
4. Recursive FIB Entry:- Recursive FIB entries indicate that the destination is reachable through some other route (Normally happens when the interface is not directly connected).

(How to check that the packets are CEF switched or Process Switched)

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