Routing question on RH9, two gateways

tscman · 11-23-2004, 11:40 AM

Hi all,

Sorry this is a pretty long post, here goes...

I have a need to connect two adsl lines to a RedHat 9 box, via two ethernet cards (eth0 and eth1).

The thing that is confusing me is getting the routes setup properly - namely the issue of gateways. The two adsl connections are on different subnets and have different gateways.

I need to be able to access both connections, and have the linux box accessable from the web via both connections, but the routing table - as configured by the network scripts at boot time - looks like this:

IP1: 1.1.1.102
gateway: 1.1.1.101
subnet mask: 255.255.255.252
dev: eth0

IP2 - 2.2.2.102
gateway: 2.2.2.101
subnet mask: 255.255.255.252
dev: eth1

eth2 is LAN...

(both IP's made up)

Code:

# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
1.1.1.102  	0.0.0.0         255.255.255.252 U      0      0        0 eth0
2.2.2.102 	0.0.0.0         255.255.255.252 U      0      0        0 eth1
169.254.0.0     0.0.0.0         255.255.0.0     U      0      0        0 eth2
192.168.0.0     0.0.0.0         255.255.255.0   U      0      0        0 eth2
127.0.0.0       0.0.0.0         255.0.0.0       U      0      0        0 lo
0.0.0.0         1.1.1.101     	0.0.0.0         UG     0      0        0 eth0

You may have noticed that the adsl connections are both bridged (RFC1483) and thus the subnets allow for only two nodes - the IPs I've got and the default gateways.

So, that's how the network scripts configure things for me at boot time, and I can access the internet and can access the box from the internet via either 1.1.1.102 or 2.2.2.102.

But what the routing table info here is telling me is: route all traffic to/from 2.2.2.102 to anywhere THROUGH 1.1.1.102 - ie. through the default gateway.

And everything breaks if I disconnect eth0 (1.1.1.102) - I can't get to the internet or access the box from the internet on 1.1.1.102 OR 2.2.2.102.

This is no good. I think what I need to do is have the ADSL IP addresses added with their unique gateways instead of 0.0.0.0 (ie. the default gateway). Is that right?

Does anyone know how I can multi-home this box and get around the problem of one default gateway?

Thanks in advance for reading such a long post

peter_robb · 11-24-2004, 11:15 AM

Time to read the Advanced Routing HOWTO, particularly Sections 4 & 5

tscman · 11-25-2004, 06:39 AM

Thanks Peter! Working my way through it...