Subject: the least-worst default

From: "Eric A. Hall" <[email-masked]>
Date: Wed, 12 Nov 2003 06:59:02 -0600

Of the three classes, the well-known address approach is the only one that
can work in all cases. DHCP and RA both have natural uses in specific
situations but difficulties in other situations, making them poor choices
as the "default".

OTOH, the well-known-address approach *can* work for everybody by default,
at least if a couple of minor changes are made. In particular, it needs to
use a multicast address rather than a unicast address -- servers won't be
able to listen on a unicast address that isn't configured in the OS, but
they should be able to bind and listen to a standardized multicast address
without any problems. And it should probably be restricted to an optype
that chooses a server, instead of being used for all queries -- this is
particularly important given the potential for spoofed answers if ad-hoc
servers are going to be allowed. Those changes can be debated separately,
of course. The important thing here is that this is the only approach that
has the potential for 100% coverage, and thus the only approach that's
suitable as the default.

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

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From: Masataka Ohta <[email-masked]>
Date: Thu, 13 Nov 2003 05:31:26 +0900

Eric A. Hall;
 
> use a multicast address rather than a unicast address

No, thanks. Any other minor changes?

> -- servers won't be
> without any problems.

But, we are talking about configuration which may or may not be
OS level one.

> The important thing here is that this is the only approach that
> has the potential for 100% coverage,

Are you saying CORE/RP/SS of CBT/PIM-SM/SSM exist 100% of the time?

Or, are you suggesting DVMRP?

What happens, if you are using some multicast protocol and your
ISP, which is running your DNS recursive servers, are using
a different multicast protocol?

Note also that CORE/RP/SS are single points of failure that, for
robustness, you must use 3 multicast addresses and three CORE/RP/SS.

Though link local multicast is OK (though link local broadcast is
enough with the CATENET model of the Internet), it does not mean
inter-link multicast is OK, either.

							Masataka Ohta