[c-nsp] Layer 2 vs Layer 3 Performance Question

Kevin Graham kgraham at industrial-marshmallow.com
Mon Jun 22 12:23:26 EDT 2009




> Hmm. I'm more familiar with the sup720/PFC3 hardware than the earlier stuff.

Sup2/MSFC2 is same switching paths as 720, only major difference is the common
lack of a switch fabric.

> What IOS version are you running? Can you "show mod"?
> 
> Are the servers & backup kit on the same linecard? If the linecard lacks a DFC, 
> then it's possible having them on the same VLAN would buy you local layer2 
> switching, versus a (potentially contended) layer3 lookup on the PFC/sup.

What local lookup are you expecting to occur on a non-DFC linecard? Unless I'm
missing something, you're looking at the exact same switching path for L2 or
L3. In terms of forwarding performance, the only major difference would be an
extreme edge case on overburdened hardware such saving a double-lookup for IPv6
by reverting to a single lookup for L2.


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