CEF operation

[moamen.elhefnawy]

hello

I have 2 questions about the CEF and its operation as it may affect my network

1- when I'm using the default route 0.0.0.0 , and I have packets routed via this default route as no specific route in the routing tables

those packets will be proccess switched or CEF switched ?

2- I know the operation of the CEF and the using of FIB table adjacency table , but what I need to know about the lookup for matching on the cef table , how this lookup done , software process or H/W proccess

Thanks & BR

Moamen

[pkhatri]

Hi,

1. Whether or not CEF is used depends on what you have configured on your router. Packets routed via the default route can certainly be CEF-switched.

2. I believe it is done in software in the lower-end platforms. It is, of course, highly optimized.

Regards,

Paresh

[pkhatri]

Hi again,

You can use the following link to determine the switching path being used by your router:

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

Hope that helps - pls rate posts that are helpful.

Paresh

[moamen.elhefnawy]

Hello,

thanks for your prompt reply , actually for the first question which is the most important , we have opened a case with Cisco TAC , and one of the engineers advised that packets routed using the default route are proccess switched not CEF switched , altough the CEF is enabled on the all interfaces

But it seems strange for me , do you have any documentation about this issue

Thanks & BR

Moamen

[pkhatri · Accepted solution]

Hi Moamen,

That is not true.. packets routed using the default route are certainly CEF-switched, if enabled.

I have just tried this in my lab and here are my results:

Before sending 5 pings:

LABCE-2651XM#show int fast0/0 switching

FastEthernet0/0

Throttle count 0

Drops RP 0 SP 0

SPD Flushes Fast 0 SSE 0

SPD Aggress Fast 0

SPD Priority Inputs 194829 Drops 0

Protocol IP

Switching path Pkts In Chars In Pkts Out Chars Out

Process 194729 19676627 193956 21470330

Cache misses 0 - - -

Fast 128892 14697688 8367 953838

Auton/SSE 0 0 0 0

Protocol DEC MOP

Switching path Pkts In Chars In Pkts Out Chars Out

Process 0 0 3256 250712

Cache misses 0 - - -

Fast 0 0 0 0

Auton/SSE 0 0 0 0

Protocol ARP

Switching path Pkts In Chars In Pkts Out Chars Out

Note that the number of packets fast (CEF) switched was 128892.

Now I did a ping from another route that went through this router and was routed via the default route.

LABCE-2651XM#show int fast0/0 switching

FastEthernet0/0

Throttle count 0

Drops RP 0 SP 0

SPD Flushes Fast 0 SSE 0

SPD Aggress Fast 0

SPD Priority Inputs 194838 Drops 0

Protocol IP

Switching path Pkts In Chars In Pkts Out Chars Out

Process 194738 19677340 193958 21470450

Cache misses 0 - - -

Fast 128897 14698258 8372 954408

Auton/SSE 0 0 0 0

Protocol DEC MOP

Switching path Pkts In Chars In Pkts Out Chars Out

Process 0 0 3256 250712

Cache misses 0 - - -

Fast 0 0 0 0

Auton/SSE 0 0 0 0

Protocol ARP

Switching path Pkts In Chars In Pkts Out Chars Out

LABCE-2651XM#

Note that the number of packets fast (CEF) switched is now 128897 - a difference of 5.

That proves that traffic routed via the default route is CEF-switched.

Hope that helps - pls rate the post if it does.

Paresh.

[pkhatri]

Looks like that output did not appear as I expected.. i've attached a text file that has the output in a better format.

Paresh.

[moamen.elhefnawy]

Many thanks for your support ,

I think that is the right answer to my question and I Appreciate your help

Thanks again

Moamen

[pkhatri · Accepted solution]

Not a problem, Moamen... There would be a serious issue if default-routed traffic were not CEF-switched !!

Pls do remember to rate posts that help.

Regadrds,

Paresh.