Multiple DHCP'd addresses on one NIC

[Rick Stevens]

Jeff Vian wrote:
> On Fri, 2005-03-11 at 15:07 -0800, Aaron O'Hara wrote:
> 
>>On Fri, 2005-11-03 at 23:56 +0100, Alexander Dalloz wrote:
>>
>>>Am Fr, den 11.03.2005 schrieb Aaron O'Hara um 23:26:
>>>
>>>
>>>>I have my firewall connected to my cable modem with one a single NIC.
>>>>(I have another NIC for my LAN).  My public NIC is set to DHCP an
>>>>address from my ISP.
>>>>
>>>>Is it possible with Fedora to setup multiple virtual adapters that have
>>>>unique MAC addresses (that I generate) that all DHCP an address from my
>>>>ISP?  This way, I'd have multiple public IPs bound to one physical
>>>>adapter.
>>>
>>>You really think the ISP would assign you several IPs this way? I don't
>>>believe that. At least it would be some kind of misuse.
>>>
>>>I suggest you ask your provider for official possibilities or rent a
>>>server with multiple public IPs in a computer center (rack center).
>>>
>>>Alexander
>>>
>>
>>My ISP officially allows for multiple dynamic IPs on a single account
>>(Shaw in British Columbia, Canada).  It's an official option, but
>>currently requires 1 NIC per IP.  I already have 3 public IPs spread
>>over 3 machines.  I want to amalgamate them to one 'box' for centralized
>>firewall purposes.
> 
> Maybe someone with definitive information can chime in here, but AFAIK
> an IP is tied to the adapter by MAC address..  Unless you have a device
> with a different MAC address it always seems to get just one IP no
> matter how many times you make a lease request.

It rather depends on the DHCP server implementation.  The vast majority
use MACs to index into their lease table, so there's generally a
one-to-one correspondence between MACs and leased IPs, but I don't think
that's a requirement.

Note that some NIC drivers allow you to bugger the MAC address, but I
wouldn't recommend it (it can wreak havoc on ARP tables and such).
Witness the unmitigated disaster that is Windows clustering with their
(rolling eyes) wonderful "virtual" MAC address creation...grrrr!

> Aliased interfaces would still have the same hardware address, so I
> don't see how this would work.

Again, it depends on the DHCP server in use and what its rules are.
----------------------------------------------------------------------
- Rick Stevens, Senior Systems Engineer     rstevens at vitalstream.com -
- VitalStream, Inc.                       http://www.vitalstream.com -
-                                                                    -
-           grep me no patterns and I'll tell you no lines           -
----------------------------------------------------------------------