Routing and switching with Cisco Catalyst 3550

Answered Question
Sep 22nd, 2010
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Hello everybody ! I use a Catalyst 3550 for routing and switching my clients to the Internet. I established a BGP session with an ISP which give me a default route for Global Access and full routing table (BGP) for Metro Access. At the moment everything is going fine, but the memory resources are low.  My question is : Is it possible to disable CEF on the switch port that is connected to the ISP ? And in this way the switch doesn't build a switching table with the bgp routes that it receives ? I receive from the ISP about 10k of metro routes and the installed memory on the switch is 64/8 MB.


Thank you in advance.

Correct Answer by Calin Chiorean about 6 years 7 months ago

If you really want, you can disable CEF on the interface like this:


conf t

int fax/y

no ip route-cache cef


Then you can check if it's disabled:


sw3-c3550#sh ip int fa0/1 | i CEF
  IP CEF switching is disabled
  IP route-cache flags are Fast, No CEF


Here:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094a83.shtml


You'll find an interesting article about how to  "Achieve Optimal Routing and Reduce BGP Memory  Consumption"

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Correct Answer
Calin Chiorean Wed, 09/22/2010 - 04:57
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If you really want, you can disable CEF on the interface like this:


conf t

int fax/y

no ip route-cache cef


Then you can check if it's disabled:


sw3-c3550#sh ip int fa0/1 | i CEF
  IP CEF switching is disabled
  IP route-cache flags are Fast, No CEF


Here:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094a83.shtml


You'll find an interesting article about how to  "Achieve Optimal Routing and Reduce BGP Memory  Consumption"

j-marenda Wed, 09/22/2010 - 08:52
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Calin,


You should not disable CEF on the Layer-3-Switch since this will disable hardware-based Layer3-Routing.

To process-switch traffic, the CPU in the 3550 is much too small.


Also, a Cat 3550 does not have sufficient memory to keep a bgp full-table, or two of them.

I would suggest to use at least one or a pair of  2821 router with 1GByte of Ram to do so,

(of course better a pair of 7201 with 2GByte of RAM).


Today, CEF ist working fine in most IOS Versions and many Cisco-uniqe features rely on it.


You may disable soft-config do save memory in BGP.


But iff you have just one upstream, you do not need BGP-full tables but only default-route,

and inject your own prefix. (You do not need bgp or an AS for that with just one connection).


just my 0.01 $,


Juergen.

Calin Chiorean Thu, 09/23/2010 - 02:01
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Juergen, I know that everybody's advice is to use CEF, and this would be the best, if possible. In some cases, you have to deal with the hardware that you have and I just answer to the original question, how and if CEF can be disabled on Cisco 3550.


Cheers,

Calin

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