Static IP distribution

Sun Jan 28 05:27:07 UTC 2001

At 11:36 PM -0500, 01/27/2001, Jay R. Ashworth wrote:

>On Sat, Jan 27, 2001 at 11:16:00PM -0500, Eric Sobocinski wrote:
> > It's possible theoretically but not in the real world.  Nice idea
> > though.  Your major headache is that DHCP isn't defined to work that
> > way.  :-)  Right now the DHCP model assumes that any static mapping can
> > depend upon a hardware identifier, usually the MAC.  It wouldn't be that
> > hard to define an appropriate DHCP option to substitute something more
> > arbitrary like a VC identifier, but to my knowledge no one has done
> > so.
>
>Perhaps I'm misunderstanding either you, Eric, or the situation, but
>DHCP client can supply a host name, can they not?  And I thought
>servers could use that to look up for a fixed address.
>
>Yes, it's configurable, rather than fixed, but at least it's *there*.
>
>Would this not solve the gentleman's problem?

Hmmm, you're right.  It gets supplied as a form of the "client identifier", 
but I've never seen a host name used, and somehow I hadn't notice on my 
recent reading of RFC 2131 that it even gives "DNS name" as an alternate 
possible use of the "client identifier" option.  [RFC 2131, page 8 et 
al]  I bow before your power of recollection.

I'm left wondering how one would enforce correct configuration of host name 
as the client identifier?  What would prevent one customer from configuring 
a machine to steal someone else's static address?  That wouldn't be much 
use for getting a second address but it would make for a dandy denial of 
service against the "someone else".

I suppose that, as long as the client identifier can be arbitrary, that one 
could issue a difficult-to-predict client identifier for each IP 
address.  Tell the customer it's their IP address contract number?  You're 
right, at least it's already there, even if the ISP discovers they have to 
modify some DCHP client software in order to implement it.

(I'm humbled)

--eric