Static IP distribution

Sun Jan 28 04:16:00 UTC 2001

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.  Beyond that, you've got to work with the problem that neither endpoint 
of a traditional DHCP session is ATM-aware.  Generally a customer 
workstation is querying a DHCP server somewhere in an ISP server farm, and 
the ATM VC covers only an intermediate part of the path between them.  I 
suppose that one could run a smaller DHCP server within each VC-terminating 
aggregation router, but that has its own set of administrative headaches, 
and again I don't believe anyone has done that.  Even if that did work, 
you'd still have the problem that ATM VC identifiers aren't globally 
unique, and keeping them locally unique has scaling problems.  And, as 
mentioned before you have problems if you have multiple addresses on one 
VC.  If the access (DSL) provider is not also the ISP, it gets even 
worse.  In other words, DHCP by ATM VC is a nice mind exercise but don't 
bother asking for it.

Not that I have any other solution in mind.

--eric

(speaking for myself and not representing my employer in any way)

At 10:35 AM -0500, 01/27/2001, Christopher A. Woodfield wrote:

>IANAAtmGuy, but could it potentially be possible to use DHCP and map IPs
>to PVCs instead of to the end user's MAC address? Even if the end user's
>MAC address changes, the PVC number shouldn't...
>
>However, this does get complex when you have multiple machines on a PVC.
>
>-C
>
> > Managing end user MAC addresses for static IP users would be a big
> > hassle.  Every time an end user changes a NIC, swaps a server out, buys
> > a new computer, they would need to put a call in because their MAC had
> > changed.
> >
> > Having DHCP assigned statics allows us to change DNS server IP's on the
> > fly with minimal implications.  It would also allow us to reassign new
> > IP space without breaking everything (end user mail/dns/etc. would
> > break).  Worst case senario is an IP subnet change would occur, the user
> > would DHCP their new "static" IP breaking any server services, but would
> > still be able to connect to the Internet.
> >
> > There were other arguments about possible DHCP spoofing agains't static
> > IP and such.
> >
>
>--
>---------------------------
>Christopher A. Woodfield                rekoil at semihuman.com
>
>PGP Public Key: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0xB887618B