setting IP address manually

[Bruno Wolff III]

On Mon, Oct 24, 2005 at 11:59:01 +0930,
  Tim <ignored_mailbox at yahoo.com.au> wrote:
> Mike McGrath
> 
> >> Though I believe the issue you may be having is that you're trying to
> >> assign the same IP address to both interfaces.  They should have a
> >> different IP address (and ideally be on a different network)  for
> >> example, eth0: 192.168.1.250,  eth1: 192.168.2.250.
> 
> Bruno Wolff III:
> 
> > No that isn't it. You can use the same IP address on different interfaces.
> 
> That's asking for problems.  IP addresses relate to interfaces, not
> machines.  Each interface should have an unique address.  You'd be
> relying on your system trying to sort out problems for you with the same
> IP on different interfaces, and that's never a good thing.

I don't think that is correct. Ethernet interfaces have mac addresses that
identify them uniquely.
As far as routing goes, that is based on the destination address, not the
source address. It is more common that you want the source address to match
the outgoing interface so that return packets are routed more efficiently,
but there are situations where you want to use the same source address no
matter which outgoing interface you use.
> 
> How's it going to do that, then?  My computer has no idea about another
> computer on my network unless it talks to it, and they don't do that
> unless I deliberately try something between the two of them.

As others have mentioned, it looks like FC4 does an arp request to see if
any other machine on the local network(s) is already using that address.