10.4 Process Switching and Fast Switching

CCNP RS 300-101, Implementing Path Control, Uncategorized

Here is a breakdown of the fast switching process as it relates to EIGRP:

  1. The EIGRP topology table informs the creation of the routing table.
  2. The routing table is referenced by the first packet in a new traffic flow with unique source and destination IP parameters, when no cache entry exists.
  3. The information is populated into the fast-switching cache. The cache also requires arp-cache information necessary to populate L2 frame header information for packet rewrite.
  4. Subsequent packets in the traffic flow are switched in hardware using the fast-switching cache entry (called fast destination lookup).

To verify the switching method, you may either issue a “show run” command and look for ip cef output, or issue a show ip cef, as illustrated below.

To disable CEF switching, issue a no ip cef from priv exec. The switching method will fallback to the next-best method (fast switching).

To disable fast switching, which is not recommended, issue a no ip route-cache on a particular interface:

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