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From: Nikos Vassiliadis <nvass@teledomenet.gr>
To: freebsd-questions@freebsd.org
Date: Tue, 14 Nov 2006 10:50:48 +0200
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Cc: jekillen <jekillen@prodigy.net>
Subject: Re: [OT]two networks, one nic
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On Tuesday 14 November 2006 07:52, jekillen wrote:
> Hello FreeBSD users,
> I have been operating under the assumption that
> the same network interface card cannot handle two
> different networks. But then I seem to have seen
> an example in one of the OReill¥ books on networking
> that had one interface with one assigned inet address
> and also aliased with another address that could only
> be on another network. If I understood that right, it
> seems to imply that I can use one Network interface
> card for at least two different networks, like so;
> 192.168.1.<somthing> and
> alias 172.0.0.<something>
> or;
> 192.168.1.<something>
> alias 192.168.2.<something>

or you can keep your secondary addresses to a
loopback interface:
ifconfig create lo1
ifconfig lo1 200.200.200.1/24
ifconfig lo1 alias 200.200.201.1/24
ifconfig lo1 alias 200.200.202.1/24
ifconfig lo1 alias 200.200.203.1/24
ifconfig lo1 alias 200.200.204.1/24
etc

> If this is possible is it accomplished via a special routing?

No, nothing special. Your box has:
network1.address1
network2.address1

your upstream router has:
network1.address2
network2.address2

If your router is willing to forward packets to/from your
addresses, everything will be correct(read bellow though).

> My concern is that I have a laptop with one network
> interface, built in,  but would like to access it both at
> a public static address and a private network address.
> Is this possible?
> 

Your private network address will not be routed by
your ISP. You have to use "real", routable addresses.
These are routable across the internet, the private
addresses aren't. They are for private use and should
be filtered.

Please give more information, if I didn't cover your
questions.

HTH, Nikos