Re: scope

["Eric A. Hall" <ehall@ehsco.com>]

on 8/8/2003 2:36 PM Rob Austein wrote:

> Ohta-san is correct that every single one of the approaches we've
> discussed has some kind of scoping constraint which, ultimately, is

This is what I was trying to point out as well.

> - RA/ND-based: if RA/ND isn't configured, discovery doesn't happen.
> 
> - Multicast-query based (DHCP, DHCP-lite, LLMNR-like, whatever): if
>   router multicast (or DHCP relay) isn't configured, may work anyway
>   on the local link, but otherwise discovery doesn't happen.
> 
> - Well-known address based: discovery propagates upstream following
>   the default route until it finds something or hits the edge of the
>   default free routing zone.  Discovery does not work if neither
>   well-known address nor default route is configured.

That's pretty mcuh right, except for a clarification to the well-known
address problem, which is that in the default (unmanaged) scenario,
locally-generated queries will follow the default routes, and will get
passed to whoever actually owns the address space in question.

There are actually two impositions here: First is that the use of an
address-based mechanism needs to have non-delegated, non-used address
space explicitly reserved for it by ICANN or whoever. Organizations don't
necessarily have to use that address space, but something needs to be
reserved for use in the default model, and it must not be part of RFC1918
space or any actual space. Second is that the use of locally-preferred
addresses actually cranks up the administrative costs greatly, since
admins not only have to configure the routing service to accomodate the
local addresses, but also needs to configure the nodes to use that address
space. None of the other requirements have any need for the admins to
manage the leaf-nodes whatsoever, and this is not a trivial artifact.

-- 
Eric A. Hall                                        http://www.ehsco.com/
Internet Core Protocols          http://www.oreilly.com/catalog/coreprot/

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