Wired Bird BGP behaviour

Dr. Christian Riede christian.riede at it-connect.de
Mon Sep 21 10:10:43 CEST 2009


i have the following setup:

--+----------+----------+----------+ NET-ISP
  |          |          |          |
Quagga1   Quagga2    Quagga3     Quagga4  Test-Quagga1  Bird
  | |        | |        | |        | |        | |        | |
--+-|--------+-|--------+-|--------+-|--------+-|--------+ | NET-1
----+----------+----------+----------+----------+----------+ NET-2

<-------official productive AS----------> <-- private test AS-->

Quagga1-4 belong to our official AS. The Test-Quagga and the Bird use
a private AS.

All six BGP-Routers in NET-1 and NET-2 are fully meshed with BGP sessions
over NET-1 and NET-2.  Only Quagga1 and Quagga2 have BGP sessions to
the ISP-Router.

On Quagga1 and Quagga2, I see about 290000 accepted prefixes on the 
BGP-sessions to the ISP router and on the two sessions between Quagga1
and Quagga2.

On Bird, I also see about 290000 accepted prefixes on all sessions.

On Test-Quagga1, I see only 3 accepted prefixes on the sessions to Bird
(the direct attached networks).  When I shut down all eBGP sessions on
Test-Quagga1, I get the expected ~290000 accepted prefixes on the two
sessions to the Bird. The routing table grows very slowly.

If I stop Bird and start Quagga on the same system, I see all expected
~290000 prefixes on Test-Quagga1 via iBGP.

It seems that Bird does not re-announce routes to Test-Quagga1 that it
learnt via eBGP if it also receives those routes from Test-Quagga1 via
iBGP. This behaviour is different to Quagga.

Is my suspicion correct?

Can anyone explain this behaviour?

What is Bird doing differently than Quagga?

Is this a sensible behaviour of Bird?

Should/can it be fixed?

Mit freundlichen Grüßen

Dr. Christian Riede
Teamleiter Technik 

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