BIRD ripng default gateway route strange behavior

[Ondrej Zajicek]

On Sat, Apr 18, 2015 at 07:14:07PM +0200, olivier a wrote:
> Hello all ^^
> 
> I'm puzzled with a really weird RIPng default gateway propagation problem.
> I don't quite understand what's happening. Here is what happens ...
> 
> Network topology :
> 
> PC1---Router1---Router2----InternetGateway---z
> 
> RIPng enabled on PC1, Router1, Router2
> Router2 has a static IPv6 DG ( Default Gateway ) to InternetGateway
> Router1 has no static IPv6 DG, and no kernel{learn} directive.
> 
> Router2=Ubuntu14.04 LTS, Router1=raspbian Wheezy, bird = last version,
> compiled from sources
> link-local addresses replaces with symbolic names ( ie [fe80::Router1] )
> 
> Something really strange seems to happen :
> 
> . Router2 gets this routing table :
> 
> default via InternetGateway dev eth0  proto static  metric 1
> default via [fe80::Router1] dev eth1  proto bird  metric 1024
> 
> But Router1 isn't announcing any IPv6 DefaultGateway, just ::/0 metric 16 (
> ie it is poisoning the route ).
> ( I checked using Wireshark ).
> 
> Is there a bug that transforms a received "::/0 metric 16" into a "default
> via [fe80::Router1] dev eth1  proto bird  metric 1024" route ?

Hi

There is a problem in RIP that routes with metric 16 are treated as usual routes
(e.g. exported to other protocols as usual routes). Best workaround would be
to limit such exports to other protocols by:

  if (defined(rip_metric) && (rip_metric = 16)) then reject;

in export filters to other protocols.

Kernel metric 1024 is just the default kernel metric in Linux-IPv6 where no
other is specified using krt_metric route attribute. This is different than
in Linux-IPv4 where the default kernel metric is 0.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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