Re: Dynamic IP address assignment


Sun ECD Software (eagle_snax!db@decvax.dec.com)
27 Nov 88 22:39:37 GMT


In article <In article <1378@aucs.UUCP> In article <1378@aucs.UUCP> wdw@aucs.UUCP (Bill Wilder) writes:

> Does anyone know of an RARP implementation that dynamically assigns
> IP addresses from a pool?

We ship one standard as part of the Sun386i workstation. We don't
encourage use of RARP for this, but the option is supported. By
default we use extensions to RARP that we call "Dynamic RARP". (An RFC
on that is in progress.) A network policy option can be changed to
also allow use of RARP, if the network administrator is convinced that
this won't affect operation of an existing network. It usually
requires some conversion, and in any case clients have to know
how to deal with temporary IP addresses they've been handed.

We use it as part of an automated system and network installation
application. When diskful or diskless systems are set up on a network
supporting automated installation, they first get an IP address using
Dynamic RARP. Then they install themselves on the network, keeping
that IP address, using an RPC protocol. The requirement is that any
user can safely install a workstation (or PC) on the network just by
plugging it in and powering it on, except in cases where a network
administrator has decided that they should not be doing this (and set
the relevant policy to control this).

> Obviously this would be appropriate only for
> machines such as PC's in a public location where the current user may
> care less what his IP address is.

There are a lot of ways to use such a feature. "Obvious" is not a
phrase I'd apply to this decision! It really depends on the
application you're constructing using dynamic address assignment.

The way we use it is to set up a network of machines where all the
system names (and addresses) have to be persistent, since each
workstation will as a rule be serving data to others. We aren't
focussing on sites with money to spend on dedicated servers, or which
have any kind of expertise in networking. After that address is
assigned, it's made permanent unless it times out first due to
some kind of error (after 1 hour).

Another way that dynamic address assignment might be used is to let a
bunch of what I call "transient hosts" access the network. Not unlike
Kinetics does with Macintoshes -- the address is bound for the duration
of a session, and the clients of the address server advertise no
network services and need no names. (But how to enforce that?) I
especially like the example of contacting a commercial TCP/IP service
provider over a dialup IP link: you don't know, or care, the IP
network address in use at either end, but you want to be able to
use the service knowing only its phone number and your own VISA/MC
information.

We've also discussed allowing automatic reconfiguration of networks.
Imagine moving a workstation from one cable to another, and having all
the naming databases (YP, BIND, etc) automatically updated with the new
addressing information. Right now, the reconfiguration requires manual
steps at a central server, but in principle it needn't.

These last two get tricky when the system has substantial "identity",
because the IP address no longer is part of that identity. How many of
the Internet security models presume that IP addresses remain constant
over very long periods? How many applications have that hidden
assumption? And how many applications can really address the security
problems of whether or not to trust their client (or server) ? Also,
hosts make lots of assumptions about their "local" environment, ones
which probably won't be valid in a different environment.

I'm curious who is working on models that don't assume centralized
administration, as with a BIND or YP server. Dynamic address
assignment without a central control site would seem to be a requirement
for small (potentially isolated) IP networks which can't afford
a dedicated server.

    David Brownell dbrownell@sun.com
    Sun Entry Systems Software sun!suneast!db
    Billerica, MA

--
David Brownell,	Sun Microsystems East Coast Division
{ihnp4,decwrl,hplabs,ucbvax}!sun!dbrownell

"There is a time and a place for spontaneity."



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