setting IP address manually

[Mike McGrath]

> -----Original Message-----
> From: fedora-list-bounces at redhat.com 
> [mailto:fedora-list-bounces at redhat.com] On Behalf Of Bruno Wolff III
> Sent: Monday, October 24, 2005 9:51 PM
> To: Tim
> Cc: For users of Fedora Core releases
> Subject: Re: setting IP address manually
> 
> 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.

This is confusing the data link and network layers.  Mac addresses have
nothing to do with IP routing.  And you could have one mac address that
has multiple IP addresses.  (For example an aliased interface, like
eth0:0)  At no point in time should two seperate machines have the same
IP address.  There's goofy ways you could force it to work by manually
editing the ARP tables on both machines but I digress.

> > 
> > 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.

	-Mike