Solved: ip route cache on 2950t switch

mahesh18 · ‎01-11-2010

Hi all,

I have 2950t switch and it has 1 vlan.

right now i have this under vlan 1

no ip route-cache

my question is should i enable it under vlan1 or not?

what are its advantages?

many thanks

mahesh

Peter Paluch · ‎01-11-2010

Hello,

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.

Obviously, 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. I don't think that the command can be even 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.

You might want to read more about the Fast Switching and other switching methods here:

http://www.cisco.com/en/US/tech/tk827/tk831/technologies_white_paper09186a00800a62d9.shtml

Best regards,

Peter

View solution in original post

Peter Paluch · ‎01-11-2010

Hello Ganesh,

Nice reply. Please allow me to add a correction, though.

The route cache allows outgoing packets to be load-balanced on a per-destination basis rather than on a per-packet basis.

This is not the main point of using the route cache. 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.

Best regards,

Peter

View solution in original post

Peter Paluch · ‎01-11-2010

Hello,

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.

Obviously, 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. I don't think that the command can be even 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.

You might want to read more about the Fast Switching and other switching methods here:

http://www.cisco.com/en/US/tech/tk827/tk831/technologies_white_paper09186a00800a62d9.shtml

Best regards,

Peter

mahesh18 · ‎01-12-2010

Hi Peter,

Thanks for great reply.

Your answer was very good easily understandable and clear.

many thanks

mahesh

Ganesh Hariharan · ‎01-11-2010

Hi,

IP route cache is used for fast switching of packets, The route cache allows outgoing packets to be load-balanced on a per-destination basis rather than on a per-packet basis. The ip route-cache command with no additional keywords enables fast switching.

Entering the ip route-cache command has no effect on a subinterface. Subinterfaces accept the no form of the command; however, this disables CEF or dCEF on the physical interface as well as all subinterfaces associated with the physical interface,enables (ingress) NetFlow accounting for traffic arriving on an interface.

Hope that helps out your query !!

Regards

Ganesh.H

Peter Paluch · ‎01-11-2010

Hello Ganesh,

Nice reply. Please allow me to add a correction, though.

The route cache allows outgoing packets to be load-balanced on a per-destination basis rather than on a per-packet basis.

This is not the main point of using the route cache. 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.

Best regards,

Peter

Ganesh Hariharan · ‎01-11-2010

Thanks for clarification Peter !!

Regards

Ganesh.H

mahesh18 · ‎01-12-2010

hi ganesh,

Many thanks for your reply too.

mahesh