gateway on one nic routing

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From: Jeff Liebermann <jeffl@comix.santa-cruz.ca.us>
Newsgroups: comp.unix.sco.misc
Subject: Re: Must I have a NIC on the same network as a router for an SCO gateway?
Date: Sat, 24 Jun 2000 09:00:57 -0700
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On Sat, 24 Jun 2000 00:47:35 GMT, Robert Side <rside@aiinc.ca> wrote:
>You can add
>a second NIC and the SCO box can route between the two networks. Or
>you should be able to alias a second IP for your NIC and route that
>way (I think???, Never done it!). Either way, make sure you turn on
>IP forwarding.

I've built a single NIC router using Linux for entertainment value and
in desperation.  (i.e. the 2nd NIC was blown, it was 3am, no spare NIC
within 25 miles, buying time, desperate, etc).  It does work.  Every
packet that is suppose to go through the router gets repeated again,
effectively doubling traffic on the network segment.  I vaguely recall
that someones arp command will complain that a single MAC address has
two IP's although that's perfectly legal for multi-homed systems.  I
had to disarm "arpwatch" to get it to cease complaining.

In some other newsgroups I tend to lurk, the issues and questions
surrounding do-it-thyself routers is common.  Invariably someone
suggests doing it with a single NIC.  From my reading and limited
experience, it does work, and only downside is the doubling of
traffic.  Of course, for an internal firewall/gateway, it's completely
useless because any workstation could point the IP stack directly at
the external router and instantly bypass the single NIC firewall.

Yeah, I guess one could save $20 and build a gateway/router/firewall
with a single NIC.  However, I don't think that what he wants.

Also, there's some web page describing how to build a firewall using
an old MacIntosh.  Since some of these only allowed a single NIC card,
it's also done this way.  (I don't recall if it's a hardware or MacOS
limitiation).

>If I am wrong with my assumption or with any of my guesses, you didn't
>supply enough info.

Assumption, the mother of all screwups.

I don't understand why he would need a 2nd gateway (to where?) when he
already has a router/gateway/firewall going somewhere.  Some clues as
to the topology and EXACTLY what one is trying to accomplish, would be
most helpful.

-- 
Jeff Liebermann   jeffl@comix.santa-cruz.ca.us
150 Felker St #D  Santa Cruz CA  95060
831-421-6491 pager   831-429-1240 fax
http://www.cruzio.com/~jeffl/sco/   SCO stuff

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