*BSD News Article 94764


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From: Tony Griffiths <tonyg@OntheNet.com.au>
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: Multiple IP adresses with FreeBSD
Date: Wed, 30 Apr 1997 17:27:40 +1000
Organization: On the Net (ISP on the Gold Coast, Australia)
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To: pierre revel <prevel@semaphore.fr>
Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:39991

pierre revel wrote:

> 
> I suppose that I can make it with the directive 'alias' in ifconfig
> but it doesn't work... It is not a problem with apache,
> I'm just trying to 'ping' the server at multiple IP addresses.

Alias' is the correct way of doing this.  However, I don't think that
adding an alias IP address to an Ethernet interface actually tells the
box to respond to ARP requests.  So if another host tries a 'ping' it
will not be able to determine the MAC address of the host with the alias
IP addresses!

> 
> If anybody has an experience of this problem, any help
> will be appreciated !

In all cases that I have come across, the host containing the alias IP
addresses is either the 'designated router' for the entire C-class, or
there is an explicit route in the default router which points off to the
target machine and all of the alias addresses are part of a sub-net that
is different to the main network on the LAN. (ie. hosts on the LAN don't
try to ARP but simply send to the default router which knowns to forward
the packet to the virtual Web server host via an explicit route).

Tony