BGP offloading (fixing legacy router BGP scalability issues)

William Herrin bill at
Thu Apr 2 23:21:08 UTC 2015

On Wed, Apr 1, 2015 at 1:01 PM, Frederik Kriewitz <frederik at> wrote:
> In
> practice the biggest problem with [Cisco 6500s] is their poor BGP scalability
> due to the CPU/memory limitations.

Hi Frederik:

Are you sure about that? I would expect you to hit the wall on the
TCAM long before CPU/RAM limitations. Check your log for errors along
the lines of "FIB_EXCEPTION: FIB TCAM exception, Some entries will be
software switched."

This might be masked as a CPU problem since routing for destinations
which fall out of the TCAM is forced up to the main CPU.

If this is your problem and you're talking about sup-720-3bxl's with a
1M TCAM, you can change how much of the TCAM is allocated to which
functions for now. Longer term, you either upgrade to something with a
bigger TCAM or you reduce the number of routes you carry by
introducing superset routes such as a default route and then filtering
out the more-specifics your customers are least likely to use.

Bill Herrin

William Herrin ................ herrin at  bill at
Owner, Dirtside Systems ......... Web: <>

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