[c-nsp] Making SUP720 cope better under BGP load

[Simon Lockhart]

All,

I'm currently using SUP720-3BXL's in my BGP border devices.  Obviously the
SUP720 is not a particularly fast CPU, so it is pretty slow at bringing up a
lot of BGP sessions.

On one particular box, I've got 250 BGP neighbours - 1 full table transit, 2
IGP to route-reflectors, and the rest are peering sessions at an IXP. Recently,
the IXP did maintenance causing the interface to drop, and it bought the box to
its knees. The "BGP Router" process takes all the available CPU while it tries
to re-establish the BGP sessions. While this is happening, the SUP720 seems to
give up processing other stuff in a timely manner - and I see MPLS LDP drop,
OSPF neighbours drop, and then BGP sessions drop due to hold timer expires.
With all these drops, it causes even more CPU load, and the cycle continues.

I've been talking to other SUP720 using ISPs, and it seems that some see this
same effect, and others don't.

Currently running 12.2(33)SXJ3

Are there any tweaks that I can apply to the IOS config to make the SUP720
cope better in this sort of situation? I'd be happy for the BGP sessions to
take a lot longer to re-establish, if it didn't kill everything else in the
process...

And, as a follow-on question, given that the SUP720 is so under-powered for
BGP, what other options do I have which would cope better? SUP-2T? Or, if
I need to move away from the 6500, what's good for BGP routing with about 
20-40G of throughput (i.e. 4-8 * 10GE ports)? How does the ASR9k or ASR1k
range fair for BGP performance?

Many thanks in advance,

Simon