OSPF Load-sharing

[udo.konstantin]

Hi,

Currently I configure two catalyst 4506E as the Core OSPF router.

I know ospf will do per default equal load-Balancing. Also I know this load-balancing depends on the switching mode. In our case this is CEF and should be done per-Destination. I think it's possible to change e load-balancing to per-packet !!

Because normally if the load-balancing done with per-destination it is possible the links are not really utilized?! So I will change it to per-packet load balancing.

How can this changed on the catalyt 4506E switch ?

Thanks

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[cadet alain]

Hi,

this is highly discouraged to do per-packet load-sharing especially if you are using udp based applications or have a firewall

in the path because firewalls don't like assymetric routing too much. But anyway the command is under the interface:

ip load-sharing per-packet

Regards.

Alain

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[Giuseppe Larosa · Accepted solution]

Hello Udo,

in CEF the IP flow is defined by IP source address and IP destination address.

a boolean EXOR of last meaninglful bits of IP SA and IP DA and an hash seed that changes only at reload is used to assign flows to equal cost links.

IF traffic is made of multiple distinct  IP flows load sharing works well with load spread on the equal cost parallel links.

As noted by Alain load balancing per packet is not recommended because it can cause out of order issues.

I even wonder if the command is available on a multilayer switch like yours

Hope to help

Giuseppe

[cadet alain · Accepted solution]

Hi Giuseppe,

indeed it seems it is not supported as far as my search has  resulted.

Regards.

Alain

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