Re: [nsp] BGP Multihoming -how to announce backup route???

From: Gert Doering (gert@greenie.muc.de)
Date: Wed Nov 21 2001 - 05:27:31 EST


Hi,

On Wed, Nov 21, 2001 at 01:10:18AM +0200, Dmitri Kalintsev wrote:
> > Depending on the routing table growth, we're currently considering not
> > accepting /24s at all, and maybe not accepting anything more specific
>
> This would get you into trouble with networks that were issued to people
> before CIDR days. There are many /24's of this sort floating around.
>
> > than a /20 in the ARIN blocks (where nothing smaller was ever given out).

Please comment on the *full* sentence :-) - we're not going to filter /24s
from Swamp space or from network blocks where /24s have been officially
given to end users. If we filter, we'll start with the ARIN (and APNIC)
blocks that have only been assigned as /20 or even bigger blocks - those
should be announced as /20 or less specific, not as /24s.

> > So: always consider if you really want to fragment a perfectly nice and
> > shiny address block. What are the benefits, what are the risks and
> > costs.
>
> Fragmenting recently obtained blocks into anything smaller than /20 is a
> marketing and administrative suicide. You'll have piles of troubles that
> will outweight any positive effects you were trying to achieve.

I agree on that. Unfortunately when looking into the BGP table, there
are a fair number of ASes that think "it is normal to announce everything
as /24 and then play tricks with different MED/prepends per /24 to get
load-sharing". This is why I repeat myself all the time... :-)

gert

-- 
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Gert Doering - Munich, Germany                             gert@greenie.muc.de
fax: +49-89-35655025                        gert.doering@physik.tu-muenchen.de



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