Cisco router ip cef

Posted on 2011-09-28
Medium Priority
Last Modified: 2012-05-12
I am migrating my config from an old Cisco router to a ASR 1001.  

Part of the config I am migrating over it not coming over, and it is a process I have never heard about.

ip cef - it is asking for additional options that I am unfamiliar with

Therefore, when I go to configure my interface, it states :

in Interface GigabitEthernet 0/0/0
        ip nbar protocol-discovery - because of the ip cef cmd issue
                       no ip mroute-cache - says to use mibs instead ?  The above command is    deprecated. Use MFIB commands instead.

What is this IP CEF (from a knowledge learning perspective)?  And what is the correct attribute that I should add to the end of this cmd ?
Question by:Elemental12
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LVL 18

Expert Comment

ID: 36806243
CEF is Cisco Express Forwarding, basically an advanced switching technology.  It used to have to be enabled, but now it's required for a lot of other technologies (e.g., MPLS) so it should be on by default in newer software.  I'm not clear on your issue -- are you saying you're getting an error because it's not enabled?  Did you have the "ip cef" command present in your old router?

MFIB is the multicast forwarding information base, which has apparently replaced the older command.

Expert Comment

ID: 36813603
Advanced version of caching..
config t
int f0/0
ip route-cache cef


Author Comment

ID: 36815171
ip cef was present on the old router, in the actual config.  I am not sure if it is one of those default hidden cmds in this newer cisco IOS.

Sanjeevloke, it took the cmd.  Perhaps it changed from a global configuration cmd on all interfaces to a cmd that is to be entered on just the interface that would be doing this ?
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Author Comment

ID: 36815206
also, I used no ip mfib cef input and no ip mfib cef output to cover the no ip mroute-cache depricated cmd; anything else you guys think I need ?

Expert Comment

ID: 36815497
you  can enable cef globally
config t#
#ip cef

it doesn't harm anything...

Author Comment

ID: 36815554
When I try to do that, it comes up with option :

ip cef ?
  accounting          Enable CEF accounting
  distributed         Distributed Cisco Express Forwarding
  load-sharing        Load sharing
  optimize            Optimizations
  traffic-statistics  Enable collection of traffic statistics

Not sure which options to use.  Looking at my old router, it only states "ip cef" in the global (not interface) cfg.  Looks like in the older IOS, you can just hit enter, without selecting options, but in the new IOS it requires you to pick one, or perhaps all.

Author Comment

ID: 36891234
anyone with more information about which options I should use/configure ?

Thanks in advance

Accepted Solution

Sanjeevloke earned 2000 total points
ID: 36891510
ip cef distributed  you should use...

Enable dCEF when you want your line cards to perform express forwarding so that the route processor can handle routing protocols or switch packets from legacy interface processors.

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