[ILUG] ADSL+leased line together

[Deim Agoston]

Hello!

We had leased line but it was too narrow for our office and work (ok, 2 years ago
64kbit/sec line was very good) and decided to install ADSL. Everything went smooth
and it's working perfectly from the ADSL point of view. But we still had the leased line.
So, the machine has got 3 NICs, and the links looks like this:

Net-----ADSL provider (dynamic IP)--------------| ppp0-eth0 eth1|---LAN (192.168.1.0/24)
    |						|		|
    |						| 		|
    |						|		|
    |----Leased line (router: 213.163.35.157)	|eth2		|
    		     (network: 213.163.35.156)	|----------------
		     (bcast: 213.163.35.159)

I want to use the leased line to provide low volume mailing lists for our clients, secondary 
DNS and so on. So, when LAN machines goes out to administer or browse the Net they
should use the ADSL line.

The problem is that the system doesn't want to recognize the configuration of
eth2. System is Debian Woody. /etc/network/interfaces follows:
auto lo
iface lo inet loopback

auto eth1
iface eth1 inet static
address 192.168.1.99
netmask 255.255.255.0
network 192.168.1.0
broadcast 192.168.1.255
auto eth2
iface eth2 inet static
address 213.163.35.158
netmask 255.255.255.252
network 213.163.35.156
broadcast 213.163.35.159

When ppp link stands up it becames the default route. And the routing table looks like this:
core-3-g5.netpo *               255.255.255.255 UH    0      0        0 ppp0
213.163.36.156  *               255.255.255.252 U     0      0        0 eth2
192.168.1.0     *               255.255.255.0   U     0      0        0 eth1
default         core-3-g5.netpo 0.0.0.0         UG    0      0        0 ppp0

OK, the problem as you may see:
When somebody wants to connect to 213.163.36.158 port 80, they come from network
213.163.36.156. The problem is that all packets go back at _ppp0_ instead of
eth2. And they never get a reply. If I just add another routing 
 route add -net 213.163.35.156 netmask 255.255.255.252 gw 213.163.35.157 eth2

 it doesn't work either. OK, I know I should remove the previous routing on eth2.
 But if I did it and routing gone, and added the line above, the kernel gave
 me an error message.

I know I just overlooked something. Maybe I couldn't solve this without
implemetnig a policy routing (I've done this before but I try to solve this
an other way)
Kernel is 2.4 so maybe I can use iptables for proper source routing.
Give me URIs, RTFMs and so on.
Thanks,
Ago