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Tuesday, January 12, 2010

Advantages of ip routecache on 2950t switch


The ip route-cache command is used on devices that perform routing to activate a so-called route cache (or Fast Switching) that speeds up the routing process by storing the result of routing table lookup in a cache, thereby improving the lookup time for subsequent packets going the same way. To deactivate the route cache on an interface, the no ip route-cache command is used.

The Catalyst 2950T does not have routing capabilities. The command no ip route-cache on the Vlan interface is there actually because the IOS is not performing any routing operations nor it has the support for that. The command cannot be removed from the Vlan interface. Simply put, it is a fixed command that results from the way the IOS for the 2950 series is built.

Click here for more information on Fast Switching and other switching methods here.

The primary function of a route cache is to speed up the routing table lookup by storing the result of the routing and header rewrite lookup for a packet into a cache organized for very fast lookups. For all subsequent packets going to the same destination, the results from the cache are used instead of looking them up again and again in the routing table and in the Layer3-to-Layer2 mapping tables, such as ARP or IP/DLCI maps. The load balancing may or may not be involved, and the per-destination load balancing is only a side effect of using the route cache.

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