CEF LAB

[reetesh]

Can someone please help me out with this concept?

The global config command ip cef enables CEF on R2

To disable CEF on an interface i run the command no ip route-cache cef

On the above lab I disabled CEF on both interfaces of R2, yet the packet is routed via FIB

  

[Martin L]

real image/real device or GNS3? what IOS version / model ? can u disable CEF in GNS3 ?  don't have access to my gns3 gear now; will check later

Regards, ML
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[Giuseppe Larosa]

Hello @reetesh ,

two notes about your tests:

you are sending traffic with source and destination addresses that are defined on router interfaces, this makes this traffic not normal user traffic.

The second note is that even if you have disabled CEF, CEF is not the only forwarding optimization method that is available to routers.

You see that you have CEF disabled but IP route cache flags are F  no CEF.

That F stands for Fast switching a less efficient method then CEF but it is still a forwarding method.

I would suggest to make tests using IP addresses that are not on the router itself but your results are correct as you have disabled CEF but not Fast switching.

Hope to help

Giuseppe

[reetesh]

Greetings

I tried to modify the lab and i included VPCS.

But it's the same result. With CEF enabled globally when i disabled CEF on both the interfaces of R2 the ICMP packet is still routed via FIB. On one screenshot we can see even i disabled fast switching on both interfaces but output is same.

I still can't make it out why when CEF is disabled on the interfaces the ICMP packets are routed via FIB. 

I ran the command no ip route-cache cef on f0/0 & f0/1 on R2

The show ip int f0/0 | inc IP shows fast switching is enabled and Fast Switching does not use FIB