[LARTC] routing mail on a different gateway

[Julien <dyna@tri-oxyde.org>]

Hi,

I have a linux box with two dsl modems on it (connection is done via 
pppoe), I'm trying to route default traffic on the primary connection 
(ppp0) and mail traffic on another one (ppp1). This traffic will come 
from the localhost.

I run Slackware 9.1 (Kernel 2.4.22), recompiled with necessary options 
for using iproute2.

According to the advanced routing howto, I did the following :

iptables −A OUTPUT −t mangle −p tcp −−dport 25 −j MARK −−set−mark 1

I use "-A OUTPUT" since I want to alter locally generated packets.

echo 201 mail.out >> /etc/iproute2/rt_tables
ip rule add fwmark 1 table mail.out
/sbin/ip route add default via [Second's ISP Gateway] dev ppp1 table 
mail.out

I get no error message, and ip rule ls and ip route show params where 
recorded, iptables -t mangle -lnV shows no problem too.

When I do telnet smtp.someisp.com 25, I see with tcpdump the packets 
going out through the interface ppp1 :

14:32:40.693429 62.212.120.196.34515 > 193.252.22.80.smtp: S 
4069327741:4069327741(0) win 5808 <mss 1452,sackOK,timestamp 929359 
0,nop,wscale 0> (DF) [tos 0x10]

But the problem is that there are originated from 62.212.120.196, which 
is the ip of ppp0, not ppp1. So packets can't take the way back.

How can I change the "from" ip of packets that are routed through ppp1 ?

Thanks for your help.

Julien

PS: I did a quite similar post in the netfilter list, and thanks to the 
guys there I succeeded solving the base problem (at start no packet was 
going out at all on ppp1) but now I know that lartc list exists, I think 
asking here is better.

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