Great Circle Associates Firewalls
(February 1997)
 

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Subject: Re: How to configure two network interface into a same subnet? -Reply
From: Michael Ryan <mike @ NetworX . ie>
Date: Fri, 21 Feb 1997 12:18:29 GMT
To: Richard Brackett <rbrackett @ dsm . net>
Cc: firewalls @ GreatCircle . COM
Reply-to: mike @ NetworX . ie

On Thu, 20 Feb 1997 08:41:39 -0500 Richard Brackett wrote:

> I don't believe that you are going to be able to make that configuration work. 
>  How is TCP/IP supposed to choose
> which adapter to use when talking to that subnet?  Any multi-adapter 
> configuration I've seen or implemented needed
> two different subnets to work.  I've done this under various unix flavors, 
> Netware, and NT.  Most OS's will allow
> multiple same-subnet addresses to a single card, but not two different cards.
> Others may have different experiences and I'd be interested in hearing
> from anyone with more depth of knowledge on the subject.

I think you've hit it on the head here, Richard.  There is a possibility
that it would work in terms of -receiving- packets, but the O/S has no
way of knowing which interface to use when -sending- packets.

I tried to do exactly this on a FreeBSD machine several months ago, but
failed to get it to work.  I sent a query to the FreeBSD mailing list,
and replies were to the effect that it can't be done (per IP rules;
not FreeBSD rules).

A machine can have individual network interfaces to several networks;
it can have many host names assigned to a single IP address; it can have
a single network interface card as its direct route to many different
networks (reaching different subnets via IP aliasing) but it can't have
two separate interfaces directly attaching to the same network (or subnet).


Bye,
Mike
<mike @
 NetworX .
 ie>
---




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