*BSD News Article 83101


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From: Ken Bigelow <kbigelow@www.play-hookey.com>
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: Two devices with same IP
Date: Sun, 17 Nov 1996 11:22:51 +0000
Organization: Erol's Internet Services
Lines: 57
Message-ID: <328EF58B.16E4@www.play-hookey.com>
References: <56ltqk$nhv@csugrad.cs.vt.edu> <56lvvc$62f$1@gail.ripco.com> <56m19m$u08@csugrad.cs.vt.edu>
Reply-To: kbigelow@www.play-hookey.com
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H. Jared Agnew wrote:
> 
> I'm sorry I must not have been clear enough, I'm talking about having two
> devices, be they ethernet cards or modems in one machine with the same IP.
> 
>     -------     192.168.0.1     --------    192.168.0.1  ---------
>     ^local net  ^ethernet card  ^dual holmed host  ^modem   ^world
> 
> Thanks
> 
> ---  Jared
> --jared@vt.edu
> 
> David Richards (dr@ripco.com) wrote:
> : In article <56ltqk$nhv@csugrad.cs.vt.edu>,
> : H. Jared Agnew <jagnew@csugrad.cs.vt.edu> wrote:
> : >  I have a friend that uses Redhat-4.0.  He was giving me flac about the fact
> : >that FreeBSD will not allow the same IP on more than one device.  I talked
> : >to a few friends and they told me that this was because haveing two devices
> : >with the same IP is against TCP/IP standards or something.  If anyone knows
> : >where I could read more about this could you please post.  Maybe a FAQ or
> : >RFC???  Thanks
> 
> : Correct.
> 
> : One system can have more than one IP address assigned to it, but it is
> : utterly WRONG to have more than one machine with the same MAC or IP
> : address.
> 
> : That Linux would allow this is no suprise to me :-)
> 
> : Perhaps he's talking about "IP Masquerade" where a Linux box can "hide"
> : several machines behind it, using it's IP address for connections to/from
> : those machines? Handy for cheap users whose ISP won't provide them with
> : additional addresses.
> : --
> : David Richards                             Ripco, since Nineteen-Eighty-Three
> : My opinions are my own,                    Public Access in Chicago
> : But they are available for rental          Shell/SLIP/PPP/UUCP/ISDN/Leased
> : dr@ripco.com                               (312) 665-0065 !Free Usenet/E-Mail!

I have no problem with that. My gateway/mailserver/Webserver/etc. is
running FreeBSD 2.1R. It uses a 33.6k modem for connection to my ISP,
and an NE2100 clone (lnc0) for my local network. Both ports have the
same IP address, and work fine with no trouble. Since they are both
attached to the same box, neither my ISP nor my local network (nor
anyone else) have any trouble indentifying this box as a unique node.

I also have no problem operating through this box to access the Internet
from other boxes on my local network, or accessing the local net from
outside.
-- 
Ken

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