I am running Centos 5.1 on a box with two network cards each connected to different networks. After booting, the wrong network card (eth1) is the primary interface (the last one to be activated, presumably). How do I get Centos to choose the other one?

Adding a couple of lines to /etc/rc.local works:

ifdown eth0
ifup eth0

... but that just does not seem like the proper way to do this.

Oh, and I'm not looking for "why don't you just switch the network cables?" ... that would work, but I've got reasons for not wanting to do that. I want eth0 to be the primary interface.

Please help.

Thanks,
Apollo

I guess I'm curious as to what you need from a "primary" interface.

From a routing point of view, your primary interface is the one that your default route will go out, and your secondary interface will support other routes that might be faster, and those routes are set specifically.

I should point out that it's a bit of a no-no for a host to have two live interfaces (see "multihoming"). However, in your case, I'm assuming that one network is the open world, and the other is some closed link (logically or physically...).

After all that babbling, I would play around with the routing table.

eth0 is the WAN (open world). eth1 is a local network. I can access the box from both sides just fine. However, DNS requests, for example, are being sent via eth1. I want them to go out on eth0.

You can just set your default route to go out that interface.

Any other services you use on your local side (mail for instance) you can set up specific routes for.

I found these links pretty easily, rather than remembering them off the top of my head:

http://www.linuxquestions.org/questi...or-eth1-95114/
http://www.cyberciti.biz/faq/linux-s...route-command/

haha. Well, after saying i didn't want to hear "why don't you just switch the network cables?" ... that's exactly what I did. I won't give the details, but it meant I had a few other minor hoops to jump through on my particular setup, but it all took about 10 minutes. Problem solved. Now I simply have the WAN on eth1.