[34090] in North American Network Operators' Group
Re: Static IP distribution
daemon@ATHENA.MIT.EDU (Eric Sobocinski)
Sat Jan 27 23:24:01 2001
Message-Id: <4.3.2.7.2.20010127220536.00c0c900@lint.cisco.com>
Date: Sat, 27 Jan 2001 23:16:00 -0500
To: "Christopher A. Woodfield" <rekoil@semihuman.com>
From: Eric Sobocinski <sobo@cisco.com>
Cc: "Kris S. Amundson" <krisa@metstream.com>, nanog@merit.edu
In-Reply-To: <20010127103541.C5911@semihuman.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"; format=flowed
Errors-To: owner-nanog-outgoing@merit.edu
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@semihuman.com
>
>PGP Public Key: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0xB887618B
