*BSD News Article 68900


Return to BSD News archive

Path: euryale.cc.adfa.oz.au!newshost.anu.edu.au!harbinger.cc.monash.edu.au!nntp.coast.net!news.kei.com!newsfeed.internetmci.com!news.ac.net!news.serv.net!not-for-mail
From: zeno@serv.net (Sean T. Lamont)
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: Can't traceroute to virtual hosts
Date: 19 May 1996 00:56:23 -0700
Organization: ServNet Internet Services, Seattle, WA
Lines: 62
Message-ID: <4nmk77$17o@itchy.serv.net>
References: <4mhaeg$f8@venus.os.com> <4nd1nv$1cn@anorak.coverform.lan> <4nhq8j$f5p@itchy.serv.net> <4nljp0$1l5@uriah.heep.sax.de>
NNTP-Posting-Host: itchy.serv.net

In article <4nljp0$1l5@uriah.heep.sax.de>,
J Wunsch <joerg_wunsch@uriah.heep.sax.de> wrote:
>zeno@serv.net (Sean T. Lamont) wrote:
>
>> >The mask should be 0xffffffff - meaning that anything on this network can
>> >be reached down this interface.... ie. only that machine.
>> 
>> From a TCP/IP standpoint, this makes little sense. All bits are significant
>> for the network, none for the host? What about IP broadcast for that 
>> subnetwork?
>
>It is already caught by the `primary' address of this interface.  Only
>the `secondary' address(es) should get 0xffffffff.  (I.e., unlike
>filename hard links, the different aliases are not uniform each
>other.)

ah, but since you're specifying 0xffffffff, the primary address isn't
on the same net as the 'aliased' address. Any subnetwork should have
one broadcast per net, which since you're specifying a 32-bit subnet
mask, indicates that there should be one broadcast address per IP#.
As a matter of fact, there shouldn't even be a way to route packets between 
that net and the other nets on your class C, but by some amount of alchemy,
 it works.

>
>From a TCP/IP standpoint, alias addresses are a DON'T DO anyway. :)
>
>-- 


I'm not sure I agree.  If you think about a machine with multiple
physical ethernet interfaces on the same box, each having a separate
interface (ed0,ed1, etc.), it's pretty straightforward. The only major
leap of faith is to say "ok, ed0.0 and ed0.1 are really on the same
ethernet interface.

As a matter of fact, this might be more straightforward way to do IP
aliasing under FreeBSD, the ability to create (to borrow the term from
cisco) a "subinterface" ed0.0, ed0.1,ed0.2, which are separate from ed0
and behaves like a real interface in every respect. 

As a further objection, I would maintain that EVERY tcp/ip connection
on a unix box has IP "aliases". Usually one for the ethernet, lo0 for
your loopback, and any slip interfaces you're using. Try configuring
apache for a VirtualHost on 127.0.0.1 ; it works on every unix box I've
worked on, regardless of whether they support ip aliasing or not!

for whatever reason, using 0xffffff00 and routing that IP# to 127.0.0.1
works just fine for me , and I will continue to use it.








-- 
Sean T. Lamont, President / CEO, Abstract Software (ServNet)  
- Internet access * WWW hosting * TCP/IP * UNIX * NEXTSTEP * WWW Development -
email: lamont@abstractsoft.com              WWW:  http://www.serv.net
"...There's no moral, it's just a lot of stuff that happens". - H. Simpson