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Re: Verio Peering Question
From: "Stephen J. Wilcox" <steve () opaltelecom co uk>
Date: Sun, 30 Sep 2001 13:10:00 +0100 (BST)



[2] Want to tune inbound traffic?  Fine... advertise those longer
    prefixes to your upstreams/peers.  But don't make the rest of
    the Internet suffer.  Communities good.  Extra routes bad.

but people dont advertise long prefixes in order to simply make
use of two providers for the sake of it, they do it in order to

IGP-into-BGP causes this, and is hardly for preferring traffic
from one upstream.

create their own unique routing policies which by definition
needs to be internet-wide

Tag a single netblock with a community or MED.  Don't split it
into two longer prefixes.  Of course, that might require inter-AS
cooperation.

but if only one provider is agg'ing it will always prefer the most
specific route regardless of tags

i would envisage all kinds of problems too where the aggregating
upstream accepts your specific routes via another isp by
mistake and then your transit traffic ends up going all round
the place.. you'd be advertising /24s to peers and all but one
transit, with primary transit aggregating up to /16 or
whatever, feels bad..

Hmmmm.  So I have customer X, who also connects to backbone B.
They advert several blocks, which I agg to 192.168.0.0/19.  B
does not agg the blocks... but I'd also agg what I hear from
B, into the same /19.  No problem here.

no problem for you, but B's other peers wont agg and they will only see
B's more specific path as valid

Or perhaps a hack... match ^[0-9]*_ and prefer it over longer
prefixes.  i.e., if you can get there directly, it's better than
going through another AS.

Your point definitely merits thought... but I'm not sure that
it's insurmountable.

i see where youre coming from but its not a part of bgp4. you could write
it into bgp5, trouble is theres a lot of routes out there less specific
and when you turn on this feature it could be very unpredictable.

the other issue is you dont really want to prefer any route, you want them
equally valid and how can you do that unless all the upstreams apply the
same tags/rules 

theres only 20000 AS's, and its the AS that is defined as having a single
routing policy not the prefixes. why cant internet routing be based on AS
announcements, yeah i know you need to rewrite everything but i couldnt
think of a better idea. :)

Steve


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