Re: OpenBGP nexthop

[Claudio Jeker <cjeker_(_at_)_diehard_(_dot_)_n-r-g_(_dot_)_com>]

On Wed, Apr 12, 2006 at 12:18:07PM +0200, Sylvain Coutant wrote:
> Hi,
> 
> OpenBSD-current amd64 from around march, 20th.
> 
> Next to a reboot, OpenBGP had a problem validating NextHops :
> 
> Nexthop              State
> x.x.x.105       invalid   vlan97  UP, Ethernet, no carrier, 100 MBit/s
> 

What was the state of the parent interface and what kind of interface is
it?

> I had about 30 addresses on different vlans in this case. This resulted
> in the BGP session being up but routes were not valid, thus not
> installed.  I tried to "ifconfig down" one vlan and it crashed the whole
> box. Once rebooted, everything was fine.
> 

ifconfig down should not crash the box. Panic message and trace would be
interesting.

> 
> There is two points about this :
> 
> - Why is this happening ? What can I do to avoid this and/or get back
> into business without crashing the system ? Could this have to do with
> the OpenBGP/kroute.c patch sent yesterday ?
> 

This could fix your problem. The Henning's kroute.c diff fixes problem
with interface state change messages. Running without it may result in
wrong reported link states.

> - Shouldn't OpenBGP drop the session if the nexthop is not valid ? In
> our case, we do announce another AS behind us. Sessions were up, so I
> believe routes were announced to everybody. But as nexthop was declared
> invalid, routes to this AS were not installed. I think this could have
> created a loop : our upstream provider was sending packets for this
> customer's routes. As we hadn't routes installed for customer's prefix,
> we were sending back the packets to upstream ...
> 

No, the session and the nexthop are two different things. The prefix is
just marked as invalid and not considered for routing.

-- 
:wq Claudio