Routing question (GRE packet vs normal traceroute)?

[Xin LI]

Hi,

A friend of mine has encountered some problem in his setup which
consists a pair of GRE peer, one running on OpenBSD and another
running FreeBSD 7.2-RELEASE; with 7.2-STABLE, there is no improvement
over the situation.  The problem we have observed seems to be related
to GRE packet not being routed as observed, here is some details:

 - The FreeBSD box has one network interface connected to two (2)
upstream network, with different IP and does not belong to the same
subnet, say, one is 1.2.3.4/24 and another is 5.6.7.8/24
 - The default gateway can be reached through the first IP address
bound to the network interface;
 - An explicit route has been configured to the OpenBSD host, the
gateway being used can be reached directly via the secondary (aliased
5.6.7.8/24) IP.
 - Both the default gateway and the explicit host route can reach the
OpenBSD route.

The problem they had is, while traceroute to the OpenBSD host can give
the desired result, however, packets that is supposed to be
transferred through the GRE tunnel, while they will be encapsulated
into a GRE packet, the GRE packet itself won't go to the explicit host
route, but end up going to the default gateway.

The friend has configured his switch to "bounce" the packet back to
the server by configuring a host route on L3 switch, and it seems that
the FreeBSD box is able to route the GRE packet to its desired gateway
this time.

Any suggestions?

Cheers,
-- 
Xin LI <delphij at delphij.net> http://www.delphij.net