Setting the outgoing IP-Address

Hi all,

I'm probably missing something easy, but I have problems in choosing which
IP-Address should be used for outgoing packets (read: I don't know how to do
it). Here is the scenario:

A debian 3.0 machine with 3 ethernet interfaces, eth0 connected to the local
network, eth1 connected to provider_A using the ip-address 212.1.2.3 and
eth2 connected to provider_B using the ip-address 80.3.2.1.

I am moving from provider_A to provider_B and while the cached DNS-Entries
on some machines in the internet still point to 212.1.2.3 the machine should
respond to both network interfaces, while the defaultroute is set to eth2.

A ping to 80.3.2.1 from outside works fine, but a ping to 212.1.2.3 enters
the machine from eth1 and the echo_reply leaves through eth2 *BUT* using
212.1.2.3 as source address for the packet.

Since 212.1.2.3 is not within the network of provider_B, his routers throws
the packet away, so my ping to 212.1.2.3 won't be answered.

Is there some way to tell the IP-stack to use the address of the outgoing
interface as source under all circumstances, even if the packet is a reply
to a packet on another interface?.

Thanks,

Uli

In article <bebt4u$oe3$05$(E-Mail Removed)>, Ulrich Wurst wrote:
> I'm probably missing something easy, but I have problems in choosing which

No, it's not something easy. But it can be done.

> Is there some way to tell the IP-stack to use the address of the outgoing
> interface as source under all circumstances, even if the packet is a reply
> to a packet on another interface?.

Your answer lies in the poorly-documented iproute2 package. Well, there
is the IP command reference, if you can find it. Ah, here's one at
http://snafu.freedom.org/linux2.2/docs/ip-cref/
I guess it's in the source package too, as a .tex file. Unfortunately I
don't know how to convert that to a useful format. <sheepish grin>
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> Your answer lies in the poorly-documented iproute2 package.

Hi,

thanks, I already found the Advanced Router Howto und used the "routing for
multiple uplinks" method from section 4.2. Works like a champ.

Uli