Re: routing mail on a different gateway

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

Julien wrote:

> Good Morning,
>
> 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 should be able to come from the localhost or the lan via 
> NAT.
>
> 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 PREROUTING −i eth0 −t mangle −p tcp −−dport 25 −j MARK 
> −−set−mark 1
> iptables −A PREROUTING −i lo −t mangle −p tcp −−dport 25 −j MARK 
> −−set−mark 1
>
> I'm not sure whether "lo" is needed.
>
> 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.
>
> But if I do telnet somemail.server.com 25, I get a timeout and no data 
> is sent via ppp1 (seen using ifconfig ppp1 or tcpdump -i ppp1).
>
> I can't figure what can be wrong nor where I should start looking for.
> I also looked in the ip-cref doc and found nothing that could help me.
>
> Feel free to ask me on any point I would have forgotten.
>
> Do you have an idea in order to solve this problem ?
>
> Thanks, in advance !
>
> Julien.
>
Now I changed iptables line to :

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

in order to mangle packets locally generated, that works better since I 
want to route local postfix's traffic.

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