Re: Virtual NICs w/different MAC addresses
From: P Gentry (rdgentry1_at_cablelynx.com)
Date: 05/05/04
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Date: 5 May 2004 11:09:24 -0700
KR <kristian.rasmussen@broadpark.no.spam.com> wrote in message news:<4097e6de$1@news.broadpark.no>...
> Is it possible to set up a virtual NIC with a MAC address other than the
> one of the host (physical) NIC, and use dhcpcd/pump/dhclient and have a
> DHCP server assign an address to it?
>
> I have Internet access via cable, and my contract allows me to connect
> up to 5 different PCs to the cable modem. The ISP uses DHCP to assign IP
> addresses, and although the 5 addressess will always be in the same
> subnet, they are not contiguous and may change from time to time.
Don't bet on the fact that they will be on the same subnet (unless the
ISP promises and offers up his privates for a breach). The "typical"
URB that acts as the CMs gateway can support up to 6 subnets on the
same _physical_ cable segment -- ugly.
> This is what I'm trying to do: I want a Linux-based firewall between the
> 'net and my PCs, and I would like to NAT the PCs behind different IP
> addresses.
So use MASQing and keep your lan IPs private _and_ under your control.
> The problem is that the firewall PC obviously only gets assigned one
> address when I run 'dhcpcd eth0'. Creating an alias and running dhcpcd
> again (dhcpcd eth0:0) doesn't work as eth0:0 has the same MAC address as
> eth0. I guess could stick 4 extra NICs in the firewall, but surely there
> must be a better way to do it?
First, it is not clear to me why you want/need to use the ISP
addresses at all -- beyond the one for your FW. Simply use MASQing at
the FW and use private addresses on the lan.
If you need to use your ISP's dhcp addresses, then you need something
like dhcrelay (man dhcrelay -- it's available on RH -- or try
http://www.isc.org/ ). This will relay the dhcp requests to the
servers and relay back the replies to the clients.
Beware -- this will make setting up your FW filter rules a much bigger
pain than if you used private (static) IPs on the lan -- IPs that
_you_ assign/control. Not to mention that your entire lan will then
be exposed/reachable from the internet -- are you _sure_ you want that
headache?
hth,
prg
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