From owner-freebsd-questions  Wed Sep 11 17:22:32 1996
Return-Path: owner-questions
Received: (from root@localhost)
          by freefall.freebsd.org (8.7.5/8.7.3) id RAA16701
          for questions-outgoing; Wed, 11 Sep 1996 17:22:32 -0700 (PDT)
Received: from monet.telebyte.nl (jvissers@monet.telebyte.nl [194.235.214.12])
          by freefall.freebsd.org (8.7.5/8.7.3) with ESMTP id RAA16682;
          Wed, 11 Sep 1996 17:22:22 -0700 (PDT)
Received: (from jvissers@localhost) by monet.telebyte.nl (8.7.3/8.6.11) id CAA00961; Thu, 12 Sep 1996 02:22:00 +0200
From: Jos Vissers <Jos.Vissers@telebyte.nl>
Message-Id: <199609120022.CAA00961@monet.telebyte.nl>
Subject: Re: Why does arp not work when ip-alias installed
To: fenner@parc.xerox.com (Bill Fenner)
Date: Thu, 12 Sep 1996 02:21:59 +0200 (MET DST)
Cc: questions@FreeBSD.org, isp@FreeBSD.org
In-Reply-To: <96Sep11.090914pdt.177595@crevenia.parc.xerox.com> from "Bill Fenner" at Sep 11, 96 09:09:02 am
X-Mailer: ELM [version 2.4 PL25]
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: owner-questions@FreeBSD.org
X-Loop: FreeBSD.org
Precedence: bulk

Bill Fenner wrote:
> >We have a network with several Livingston portmaster and a
> >cisco router as gateway. Most of the dial-up ip addresses are on
> >the same class c network as the servers and therefore arp -a
> >should give the ethernet address of the portmaster for an
> >address that is in use.
> >
> >It does on machines without an ip-alias.
> >It doesn't on machines with ip-aliases.
> 
> Are machines with IP aliases still able to contact these hosts?

No, they cannot be reached:
PING usquebauch.telebyte.nl (194.235.214.23): 56 data bytes
ping: sendto: Host is down
ping: wrote usquebauch.telebyte.nl 64 chars, ret=-1

This is my own machine at home, I could log in to another
server and then telnet to this one so it should definitely
have been reacheable. From the dial-up host the server just
doesn't respond. It apparently knows how to get packets to
the server, but the server doesn't know how to get them back.

> What does "netstat -nr" show on the machines with aliases?

Without routed it shows nothing abnormal until you ping one of
the dial-up hosts that are connected at the time.
It wil not show in the routing table and arp -a shows:
usquebauch.telebyte.nl (194.235.214.23) at (incomplete)

If I run routed it shows the portmasters ip as gateway which is correct:
usquebauch         pm2.nmg            UGH         0        3       ed0

but arp -a doesn't show any of the dial-up hosts.


It did some further testing and it only appears to happen
when I add an ip-alias in another class-c network.
I used "ifconfig alias 193.67.242.20 netmask 0xffffff00" and
the machine's regular ip address is 194.235.214.65

When I remove the alias again it refuses to start working.

The problem doesn't occurr when I define aliases in the same
class-c with - of course - a netmask of 0xffffffff.

Is this my error? Should I use 2 different ethernet cards
when using different class-c addresses on one machine?
Another of our servers with 2 cards doesn't have this problem.

Thanks for the help, Jos

-- 
   Jos Vissers, System administrator Telebyte