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Re: Thinking differently about the site local problem (was: RE: site local addresses (was Re: Fw: Welcome to the InterNAT...))

2003-03-31 15:26:59
On Mon, 31 Mar 2003 16:12:51 -0600
"Matt Crawford" <crawdad(_at_)fnal(_dot_)gov> wrote:

All right, how do you make internal site communications completely
oblivious to a change in your externally-visible routing prefix?

You declare that any app that keeps connections around for more than
some time period T (say for 30 days) have a mechanism for
detecting and recovering from prefix changes. That solves the
problem for all apps, not just for local apps. 

Ah, well, if we're allowed to solve problems by fiat, let's just
declare that everyone "do the right thing" about site-local
addresses, automatically drop unauthorized packets, end hunger and
violence, and brush their teeth.

well, it's about like declaring by fiat that all apps should always use
DNS names, that apps should never use IP addresses, and that DNS should
be aware of network topology -- without bothering to consult with apps
writers to see whether this will actually work.

look, we've basically got three choices for address stability.  either 

(a) sites never renumber, 
(b) they renumber occasionally, or
(c) they NAT.  

we haven't figure out how to make (a) work and allow routing to scale,
or to allow enterprise networks to split or merge, etc.  we have tried
very hard to work around the problems with (c) and failed miserably. 
(b) is the only remaining option.  so it's not so much a matter
of declaring 'by fiat' that apps need to be able to survive renumbering,
as setting expectations for which apps need to be able to survive
renumbering while they're running.  and it appears feasible to set
expectations in such a way that most apps need not worry about it.

Keith



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