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Re: Max Prefixes Configured on Customer BGP

  • From: Leo Bicknell
  • Date: Fri Aug 16 09:29:30 2002

In a message written on Thu, Aug 15, 2002 at 11:41:17PM -0400, Richard A Steenbergen wrote:
> IMHO, using only prefix limits on a customer is actually doing them (and
> the rest of the internet that listens to your announcements) a disservice.

I think you might be missing a highly useful case of using max-prefix
with customers.  Many customers will want to deaggregate their
blocks, and/or leak more specifics.  While I don't want to argue
if that is good or not, the end result is most ISP's allow this in
some form.  Consider the difference between:

Case 1: a.b.0.0/16 exact match prefix filter

        Customer calls in, asks for change.

        a.b.0.0/17 + a.b.128.0/17 exact match prefix filter.

Case 2: a.b.0.0/16 le 19, max prefix 6

The second case allows customers to make changes with no delays,
and reduces the amount of work for the ISP.  It still enforces some
level of aggregation automatically to protect the system, but also
gives the customer some flexability.

Generally I'd recomend something around twice the number of prefixes,
with some sort of floor.  So, if you registered 200 prefixes, you
could announce 400 routes from them, with a maximum length as set
by your ISP.

       Leo Bicknell - - CCIE 3440
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