3750 CEF & equal-cost load-balancing - software CEF & ASICs?

[andrew.butterworth]

We are trying to tune CEF on a 3750 stack (4 * 3750-12S) and have hit an issue whereby the CEF commands don't change anything for the hardware forwarding path.  We have four routed Gigabit interfaces that each has an OSPF adjacency and we are learning the same route via each of these links and we want to load-balance over them.  Our client IP addressing is such that we aren't getting an even split on egress so we would like to try and tune CEF. What we are seeing is no way to tune the hardware forwarding path.

For example the 'ip cef load-sharing algorithm' changes how the software CEF path is determined which you can check with the 'show ip cef exact-route' command.  However if you check the hardware forwarding path with the command 'show platform forward' this doesn't change.

According to the documentation the dCEF commands on the 3750 only relate to the software forwarding path:

'Because the switch stack uses Application Specific Integrated Circuits (ASICs) to achieve Gigabit-speed line rate IP traffic, dCEF forwarding applies only to the software-forwarding path, that is, traffic that is forwarded by the CPU.'

So is there anyway to tune how the hardware CEF tables are determined?

Cheers

Andy

[cadet alain]

Hi,

As PBR can be Fast-switched  would it be an option for you to split the load using this feature ?

Regards.

Alain

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[andrew.butterworth]

PBR is a possibility, however it will be more complex and will require some tracking to be configured to cater for any failures that occur - PBR is just static routing at the end of the day....  I'd rather rely on the routing protocol to take care of any failures.

It appears the behaviour is very similar on a C6K Sup720 we are also testing with (i.e. software and hardware CEF paths), however with the Sup720 we can tune things with the 'mls cef ip' commands - these commands aren't available on the 3750.  It seems the hardware CEF switching just isn't configurable on the 3750/3560.

Andy