Using 2 NICS?

Karl Bellve Karl.Bellve at
Wed Oct 25 11:53:30 PDT 2000

Robert Ross wrote:
> What do you mean "Linux is assigning both IPs to the first NIC"?
> Something like:
> # ifconfig eth0
> # ifconfig eth1

Right, this is the way I set it up.

However, it appears that one of the NICs seems to be used for both IPs.
I am not sure why this happens. I can disconnect NIC #2 and still ping
both IPs. If I disconnect NIC #1 and connect NIC #2, I can no longer
ping either IP. If I use ifconfig -a, it reports correctly. Each NIC has
its own IP, MAC address, mask, interupt etc. I was told that Linux
assigns both IPs to the first working NIC card (eth0) when the networks
are the same.

> doesn't work?  It would be a terrible change in the semantics of ifconfig
> if it didn't.  I have done this more than once, but not under RH7.0 or
> Linux 2.4.  I would be surprised if it were impossible to do now though.
> Perhaps what you mean is "the way I have my RedHat machine configured
> keeps putting both IP addresses on the same card and I don't know how to
> fix that"?
> Rob
> ---
> Rob Ross, Mathematics and Computer Science Division, Argonne National Lab
> On Wed, 25 Oct 2000, Karl Bellve wrote:
> > The question is, is it possible to use two NICs with their own unique IP
> > on the same subnet? I would then allow half of our computers to connect
> > to one IP and the other half to the other IP. I know this isn't load
> > balancing but I think this should be doable.
> >
> > Right now, Linux is assigning both IPs to the first NICs since they have
> > the same netmask and gateway.


Karl Bellve, Ph.D.                   ICQ # 13956200
Biomedical Imaging Group             TLCA# 7938 		
University of Massachusetts
Email: Karl.Bellve at
Phone: (508) 856-6514
Fax:   (508) 856-1840
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