On Fri, Apr 20, 2007 at 02:02:18PM -0400, Ralph Droms wrote:
> Set up the relay agent in your router to point at my DHCP server.
There are also DHCPINFORM (v4) and Information-Request (v6) messages
which can transit the public Internet. I think however, v4 fails
with NAT.
They are also not widely used for this purpose at the moment.
I was thinking about this while swimming yesterday.
Phillip's abstract problem is that multiple administrative domains
exist.
There is the physically attached network, which represents one
administrative domain which reaches to every place the broadcast
domain touches. Someone is responsible for that network, and
the services it provides which facillitate access.
There is his 'home' network, which represents a second administrative
domain.
There is his 'work' network, which represents a final third domain
(or more).
It is likely that each of these three domains will wish to present
dynamic configuration contents.
One subset of them are only contextually useful when the physical and
administrative domains match (such as "what's the default gateway?"
and "where on earth is the network port I'm attached to?").
A second subset of them are contextually useful no matter where on the
Internet Phillip's laptop is connected (such as "where is my Inbox?"
or "where should I send my lat/long to?").
Right now, DHCP(v4|v6) has only been used to solve for the case where
the physical and administrative domains match. Operationally.
DHCPv6 could easily be used for the case where the administrative
domain is extra to the physical broadcast domain by making use
of the Information-Request, and sorting values fetched this way
ahead of values got off the link.
DHCPv4 could potentially also be used for the same case, as the same
message exists, but we would need to introduce a signal for alternative
server behaviour ("reply to source address and port") to work around
NAT if that were desirable.
Both would require a single manual configuration element - the
address(es) of the DHCP servers the laptop wishes to acquire
super-administrative configuration from. Probably delivered as
a domain name, possibly also advertised eg via DHCP while the
client is on the administrative domain's physical links.
Firewalls or NAT, even if a problem, really aren't, since software can
cache old values until it can freely observe the system again. This
is just the same as network partition or packet loss problems.
--
David W. Hankins "If you don't do it right the first time,
Software Engineer you'll just have to do it again."
Internet Systems Consortium, Inc. -- Jack T. Hankins
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