David Conrad wrote:
How do you renumber the IP address stored in the struct sockaddr_in in a
long running critical application?
...
If you had a separation between locator and identifier, the application
could bind to the identifier and renumbering events could occur on the
locators without impacting the identifier.
For a long time I've suggested that we begin to look anew at the idea of
an "association" as an abstraction over "transport". Yes, I know that
this smacks if ISO/OSI, but there were a few granules of good ideas there.
The idea is this: An "association" is an end-to-end relationship
between a pair of applications that potentially spans several transport
lifetimes.
Then, if the underlying transport goes away, perhaps due to movement in
a mobile network or renumbering, then the association is reconstructed
on a new transport that is built in accord with the current addressing
and routing conditions.
Reconstruction does not, as some have assumed, require that the network
remember anything or hold any state. Rather, taking a cue from ISO/OSI,
the trick is that the association layer is merely a means for the
applications to reliably exchange checkpoint names. What those
checkpoint names mean is up to the applications - thus what to do if a
rebinding to a new transport requires going back to a checkpoint is
something entirely within the application and its networking library
code, not some state that is stored in the net.
Basically whenever applications establish a transport they say "Ahem,
where were we when we last spoke". One answer is "We did not last
speak" Another answer is "we last agreed on the checkpoint named
'foo'". How they recover from 'foo' is entirely application dependent.
(I have not really considered the security implications - in the absence
of some form of shared secret or other authentication on association
re-establishment there would probably be a race condition in which an
intruder could jump in.)
(I'm also thinking of TCP based applications, not UDP based ones. For
them I don't see renumbering as much of a problem, but I may not be
seeing enough.)
This is not something that can readily be transparently back-ported into
existing protocols; it's not something of trivial import. But it can be
deployed for new applications and not invalidate either existing
applications or existing application protocols.
And consider, for example, how something like this might have obviated
the need for the IP layer triangulation in mobile IP.
--karl--
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