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Re: bgp update destroying transit on redback routers ?
From: Olivier Benghozi <olivier.benghozi () wifirst fr>
Date: Thu, 1 Dec 2011 20:03:06 +0100

Alexandre Snarskii <snar () snar spb ru> wrote:
AGGREGATOR is an optional transitive attribute of length 6.
            The attribute contains the last AS number that formed the
            aggregate route (encoded as 2 octets), followed by the IP
            address of the BGP speaker that formed the aggregate route
            (encoded as 4 octets).  Usage of this attribute is described
            in 5.1.7

And what to do with 4-byte AS-numbers then? That would explain the 8 bytes.


we also have some issues with this here, the update message the Redback logged is:

ffff ffff
ffff ffff
ffff ffff
ffff ffff
0049  02
4001 01 00
4002 12   02   04   00000513  00000d1c  0000b611  0000b611
4003 04 50ef82c1
4006 00
c007 08 00 0000 0000 0000 00
16 ce7d a4

The prefix is, AS-PATH is 1299 3356 46609 46609 (Telia, Level3, and finally Hostlogistic with one 
The AGGREGATOR is full of 0. I guess this could be what bothers the Redback/Ericsson code.

I see the same route by other sessions, and the aggregator looks OK, since the sh bgp says:
8218 4436 46609 46609
  Origin incomplete, localpref 100, med 100, weight 100, external, best
  aggregator:, AS 46609, atomic-aggregate

So Hostlogistic route to Level3 is malformed (according to the RFC, the AGGREGATOR content is mandatory if the 
attribute is present), but their route to NLayer is OK. Or maybe a Level3 router has a problem?
Anyway, our Redback/Ericsson routers are the problem now, since the other vendors don't throw away the BGP sessions...
I've opened a case at Ericsson, still waiting for an answer :-/

Olivier Benghozi

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