Subject: [mobile-ip] Dynamic Interfaces (was: 50 ms RA timer?)

From: Scott Corson <[email-masked]>
Date: Tue, 26 Nov 2002 15:52:30 -0500

> for Internet connectivity.  Mobile IP seemed to be quite well-regarded
> as a beneficial technology there.  I mentioned a couple of my
> pet peeves about current 802.11 device drivers and delays, and
> I got the impression that many (not all!) IEEE engineers in the
> meeting wanted to ensure that future products would work well
> with Mobile IP.

Increasingly, as the understanding permeates the industry that link layers
come and go, yet IP remains, link layer folks will begin to explicitly
design (or minimally to optimize) their technologies to plug into the
underbelly of an IP network.

The best thing the IETF could do IMHO would be to begin to *help* these
folks out.  

There is an increasingly broad class of link layer technologies under
development that, collectively, exhibit very 'dynamic' behavior.
Intermittent and varying connectivity is the norm, not the exception, for
this class of technologies.  And they need not be mobile technologies,
although this is the common case.

I think the IETF should define (or put into common practice) what is
essentially a new interface type--a "dynamic" interface--to be chosen for
use by these technologies if desired.  It should likely retain the
addressing semantics of a 'broadcast' interface--link layer unicast,
broadcast and multicast--yet ensure that the efficient, dynamic discovery of
'point-to-point' relationships between neighboring interfaces (generally
thru link layer mechanisms) can be communicated to the IP stack in a
standard way.  This mechanism would enable an IP stack to interact with this
new interface type in new ways.  This essentially requires standardizing
IP's "underbelly"--a term that Phil N. recently introduced on the PILC
list--to understand and work with dynamic interfaces.  

A 50ms RA timer is a pretty blunt instrument for assessing next-hop
reachability, and is inapplicable in many deployment scenarios.  If that is
the best you can do, then perhaps that is an answer, but it's certainly not
THE answer.  

A dynamic interface construct would be extremely general, and would likely
solve the problems that the recent interest in work on L2 triggers has hoped
to address.  It would apply to many technologies, and be useful in many
contexts where Mobile IP, MANET, Nemo and other such network layer protocols
must deal with link layer dynamics in a timely fashion.  It should also be
understood that the prerogative to act, to delay or to suppress these events
is still under the control of the IP layer.

-Scott