ISP Cutover - Multip NICs on NATed Linux Box

I am cutting over to a new ISP and have I have a linux box on my
internal network which has a reverse NAT to its ssh port. I'm in a
situation where I'd like the box to be available concurrently to both
the current public IP address and the new public IP address for a two
week duration.

The box now has only a single NIC card. I have setup a second firewall
created for the new ISP connection.

I like to add a secondary NIC card, eth1, and configure it to route
through the second firewall to the internet. However, I feel I may
have a routing issue, as my eth0 NIC is routing out through the current
firewall to the internet.

Is there a way to setup routing so that the box will respond to ssh on
both public IP addresses?

Thanks,

-Eric

On Mon, 10 Apr 2006 11:45:52 -0700, ecross wrote:

> Is there a way to setup routing so that the box will respond to ssh on
> both public IP addresses?

With source-based routing, you can have packets sent by your machine with
a NEWIP source address routed to the new router and packets with an OLDIP
source address router to the old router.

You can use /sbin/ip to do this, but there may be a more friendly way;
it's been a long time since I played with this. For example:

/sbin/ip rule add from NEWIP to default table 5
/sbin/ip route add to default via NEWROUTER table 5

sets up a route table which does what you need for NEWIP.

I did a quick search on source-based routing, and I see that iptables can
also be used to do this. So that's another possible approach.

This article:
http://www.linuxjournal.com/article/7291

appears to discuss my solution in more detail.

I've no idea whether ip or iptables is the better approach.

- Andrew

Thanks for your reply Andrew. I ended up following this very clear
guide here:

http://www.tldp.org/HOWTO/Adv-Routin...ple-links.html

Good stuff.