CEF load balancing per packet on 4500

Unanswered Question
Feb 16th, 2010

hi,

i need to know is the feature of CEF load-balancing per-packet supported on 4500 switch or not?

if not supported how i can make per-packet load-balancing in another way......

thx

Adham

I have this problem too.
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Jon Marshall Tue, 02/16/2010 - 08:39

adham.mohamed wrote:

hi,

i need to know is the feature of CEF load-balancing per-packet supported on 4500 switch or not?

if not supported how i can make per-packet load-balancing in another way......

thx

Adham

Adham

No it is not supported on the 4500, only per destination load-balancing is supported. You can't do per-packet load-balancing with CEF and as far as i know there is no other way to do it. You would need to install a router upstream to be able to do this.

Jon

Adham mohamed said Tue, 02/16/2010 - 08:47

Thanks for confirmation - But if I put a command # no ip route-cache under the vlan interface which face the two balanced links, this will lead to per-packet behavior but in cpu processing Not hardware processing provided by CEF. correct me if I'm wrong.

Best Regards

Adham Abdallah

Network Engineer

Summit Technology Solutions

Jon Marshall Tue, 02/16/2010 - 09:02

adham.mohamed wrote:

Thanks for confirmation - But if I put a command # no ip route-cache under the vlan interface which face the two balanced links, this will lead to per-packet behavior but in cpu processing Not hardware processing provided by CEF. correct me if I'm wrong.

Best Regards

Adham Abdallah

Network Engineer

Summit Technology Solutions

Can you actually put that command in ie. "no ip route-cache" ? As far as i am aware you cannot disable CEF on a 4500 but i could be wrong.

Jon

Adham mohamed said Tue, 02/16/2010 - 09:14

Yes I can put int under vlan interface. My assumption is to enable legacy route-cache load balancing per packet.

Best Regards

Adham Abdallah

Network Engineer

Summit Technology Solutions

tdistlists Tue, 02/16/2010 - 12:51

Hey,

I think you can only disable dCEF for your linecards on a 4500, but not disable CEF completely -- with the #no ip cef distributed command, but this will just lead to centralized cef switching.

Can you issue the following command and see what output you get after you issue the ip route-cache command?

I just tried on one of my 4500s and I can't issue that command.

#sh cef int vl2216
Vlan2216 is down (if_number 209)
  ...
  Hardware idb is Vlan2216
  Fast switching type 21, interface type 156
  IP CEF switching enabled
  IP CEF switching turbo vector
  IP prefix lookup IPv4 mtrie 8-8-8-8 optimized
...
Ganesh Hariharan Wed, 02/17/2010 - 03:11

Yes I can put int under vlan interface. My assumption is to enable legacy route-cache load balancing per packet.

Best Regards

Adham Abdallah

Network Engineer

Summit Technology Solutions

Hi Adham,

Cat 4500 series switches support per-destination and Load Sharing Hash Function, check out the below link on further information.

http://72.163.4.161/en/US/docs/switches/lan/catalyst4500/12.2/31sga/configuration/guide/cef.html#wp1146775

and no "ip route-cache" starts process switching, in which each packet is checked for source and destination IP from the routing table. You get per-packet load balancing if you have more than one path to the destination.

Hope to help

If helpful do rate the post

Ganesh.H


Giuseppe Larosa Wed, 02/17/2010 - 03:28

Hello Adham,

>> My assumption is to enable legacy route-cache load balancing per packet.

given the multilayer switch nature of the platform this is :

a) not recommnded at all

b) possibly ineffective depending on multilayer CEF implementation you could end up with just process switching packets that would be sent to main cpu.

Depending on what device is on the other side you should consider:

a L2 or L3 etherchannel can be used

Hope to help

Giuseppe

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