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North American Network Operators Group

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Re: Max Prefixes Configured on Customer BGP (WAS Re: ALGX problems?)

  • From: Joe Wood
  • Date: Thu Aug 15 21:16:55 2002

On Thu, 15 Aug 2002, Richard A Steenbergen wrote:

> If you're using a Cisco, and they leak, their session stays down until a
> human clears it. It also does very little to prevent leaking of a single
> route (like one of Phil Rosenthal's /24s), impacting someone else. As a
> customer, I would always insist on being prefix-listed and not
> prefix-limited.

The intent of this discussion isn't whether prefix-filtering is
appropriate or not. It is up to the individual ISP to determine what
degree of filtering is appropriate for their BGP customers.

However, for ISP's that do NOT use any sort of prefix filters, wouldn't
you prefer that your BGP session was limited to a number of prefixes, in
case of a routing leak?

While leaking a /24 may be impacting, it (in most circumstances, don't
beat me up over this one) is not nearly as impacting as leaking a whole
routing table.

> I far prefer a prefix list automatically built from IRR entries, with a
> NOC and even a website capable of triggering a manual update if you need
> to get routes out now. It's all a bit of a hack, but its workable. IMHO AS
> Path filters are useless and redundant if you have proper prefix-lists.

I would also prefer prefix lists that were built automatically from an
IRR, with a manual update feature.... If you find a provider who can
claim to do this, let me know :) The best I've found is providers who can
manually add entries into the filters, and let them update off the IRR
once you've added the proper route object. Most providers that I've dealt
with (that configure off an IRR) won't even touch their filters, and will
only allow the once a day update.


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