Technical data

System Administration

303561-A Rev 00

8-79

Slot/Internal Cache

The router operating system maintains an “internal” cache storage space on (and

for) each slot in the router. This slot-level, internal cache stores routing

information captured from traffic originated on the router. For example, the PING

protocol, the IP protocols, and TFTP can each generate their own traffic destined

for IP address locations internal or external to the router.

The internal cache provides to such protocols a local, high-speed database of best

routes from that slot to any other IP destination address in your network.

If the protocol application cannot find in the internal cache a route to the desired

destination, then it searches the main routing table to find one. Once the

application finds a route in the main routing table, it adds that route to the internal

cache for the local slot.

If the routing table changes (with old routes replaced by new routes), the changes

also propagate to the internal cache on the same slot.

The internal cache is limited and fixed in size, and operates on a first in first out

(FIFO) basis. For this reason, cache entries (routes) also have a finite lifetime

determined by the size (depth) of the internal cache. The larger the size of the

internal cache, the longer it takes for an entry in that cache to disappear.

With the

command, you can examine:

• The entire contents of the internal cache on any slot

• A subset of the total contents of the cache on any slot

To view the internal cache on any slot, enter the

command using the following

syntax:

ip cache 255.255.255.255

<s>

is a slot number.

255.255.255.255

is the default address bit mask for the internal cache on any slot.