what is the purpose of enabling "ip mroute-cache" and "ip route-cache"

[chinna_22]

Hi,

I want to know what is the purpose of enabling "ip mroute-cache" and "ip route-cache" on a cisco router.

[sundar.palaniappan]

Hi,

ip route cache - Enables fast switching. Fast switching is enabled by default on most interfaces.

ip mroute-cache - Enables IP multicast fast switching.

In other words, both commands enable fast switching on an interface - one for unicast traffic and the other one for multicast traffic.

Regards,

Sundar

[chinna_22]

Hi Sundar,

Thanks for your reply.I need one more clarification here.In my case i am enabling the fast switching both for unicast and multicast traffic on a interface.But i see the "no ip route-cache cef" added automatically on the same interface.Is this the expected behaviour, if so what exactly the reason for this behaviour.

Appereciate your quick response.

Regards

Chinna

[sundar.palaniappan]

Chinna,

What you are seeing is normal behavior. It appears you have CEF enabled globally in the device and when you configure fast switching on the interface it automatically disables CEF switching for just that interface.

Regards,

Sundar

[chinna_22]

Hi Sundar,

Thanks a lot for your reply.

Need one more clarification here, what are the advantages of fastswitching over CEF?

Regards

Chinna

[sundar.palaniappan]

Chinna,

Cisco recommends CEF over any other switching method because of it's efficiency. Selecting the best switching method depends on your network setup and the type of equipment used etc. The following link will guide you in choosing the right switching method for your network.

http://www.cisco.com/warp/public/105/20.html

Hope that helps!

Regards,

Sundar

[chinna_22]

Hi,

In our lab scenario, the "CEF" is enabled on the router globally (ip cef), but the fast switching is enabled on the Interface (Multilink).How exactly the router behaves in this case, enabling CEF globally and disabling CEF on an interface.In what context we generally configure router as above.

Appreciate your response on this.

Regards

Chinna

[chinna_22]

Hi,

In our lab scenario, the "CEF" is enabled on the router globally (ip cef), but the fast switching is enabled on the Interface (Multilink).How exactly the router behaves in this case, enabling CEF globally and disabling CEF on an interface.In what context we generally configure router as above.

Appreciate your response on this.

Regards

Chinna

[sundar.palaniappan]

Hi,

I don't know if you are using a older IOS. Cisco documentation states, enabling fast switching on an interface will cause CEF to be disabled on that interface. However, in my lab routers, running 12.3 code, I am not seeing the same behavior i.e when i configure fast switching, on the interface it doesn't disable CEF.

I cannot think of many reasons why fast switching would be superior to CEF. One such reason is CEF is known to have lot of bugs and that might be a situation calling for turning off CEF. If you are not in that situation then go ahead and configure 'ip route-cache cef' under the interface.

Regards,

Sundar

P.S. Pls. rate all helpful posts.

[chinna_22]

Sundar,

Our lab router is running on 12.2(15)MC2e.

In our case the CEF is enabled globally on the router.

"ip cef" is appearing on the global configuration.

But fast switching is configured on an multilink interface.On the interface if i cofigure fast switching , the CEF is disabling as you said automativally.

By question is in this case how the router behaves as CEF is enabed globally and fast switching on an interface?

Thanks

Chinna