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Re: A simple question

2003-04-20 10:10:20
At 07:20 PM 4/19/03 -0400, Keith Moore wrote:
>   | To assign more than one address to every host means the host must have
>   | an intelligent means of deciding which address to use.
>
> Yes, but the amount of intelligence actually needed is pretty minimal.
> (It is actually harder to decide between multiple available global
> prefixes, than to decide between global and site local - the former is
> a difficult problem, the latter is almost trivial).

disagree.  the app can choose any global prefix and reasonably expect it to
work,

I completely disagree with this assumption. Firewalls and address filters mean that no app can make any reasonable assumption. Some addresses will work and others will fail. The app is left with no clues as to why the connection failed. Assuming it's just a link failure and retrying sometime in the future things will work is a receipt for user frustration.

modulo link failures. but when choosing between a global and a site
local the app needs to know whether the site local address will be valid for
the hosts that need to use it, and it has no way to know this.   the app may
also have to choose which interface to use with the site-local prefix,
and it has no good way to know this either.

The decision process is not forced on the app/host by the existence of the site-local prefix. It is due to the emergence of firewalls and address filters. The reality is that non-global routing scopes exist today. The question is - how do we provide some feedback to apps that they are trying to cross a scope boundary that it's a permanent error condition (5xx in SMTP verbiage)? One proposed notification method is the site-local prefix. Other methods can be created, but something needs to be done and simply killing site-locals and ignoring the underlying scoping issue is a non-starter.

Rich

------------------------------------

Richard A. Carlson                              e-mail: 
RACarlson(_at_)anl(_dot_)gov
Network Research Section                        phone:  (630) 252-7289
Argonne National Laboratory                     fax:    (630) 252-4021
9700 Cass Ave. S.
Argonne,  IL 60439




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