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Date: Tue, 31 May 2005 07:07:48 -0400
From: Aziz Kezzou <french.linuxian@gmail.com>
To: freebsd-hackers <freebsd-hackers@freebsd.org>, 
	freebsd-net <freebsd-net@freebsd.org>
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Cc: 
Subject: Routing loop + raw IP packets : looking for clues ...
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Hi all,
For the purpose of my project I am simpulating a 3-hop network with
QEMU on my workstation, as follows :

|---------------------------------|          =20
|-------------------------------|            =20
|-------------------------------------|
|Daemon1(user process)|---tun0---| Daemon 2 on QEMU |---tun1---|
Daemon 3 (user porcess) |
|---------------------------------|           =20
|-------------------------------|           =20
|-------------------------------------|

My workstation  is running FC3 and QEMU is running FreeBSD5.3
I am tryning to exchange raw IP packets between daemon 1 and 3 through
daemon 2. I've succeded to by pass  the system routing and get packets
sent from daemon 1 to daemon 2 and from daemon 2 to daemon 3. BUT, on
daemon 3 I can not receive them ??!!

However, when I listen with tcpdump on tun0 and tun1 I see the packets
travelling as expected :
daemon1(192.168.0.1)------>(192.168.0.2)daemon2(192.168.1.2)------>
daemon3(192.168.0.2)

What could prevent me from receiving packets intended for daemon 3? I
am suspecting some hard coded rule to prevent routing loops (which is
my case) in the Linux kernel, am I on the right track ?

Note : I disabled completely my firewalls, so this could not be the reason.

Any help is highly appreciated.

-aziz