Re: Persistent applications-level identifiers, the DNS, and RFC 2428
2003-10-01 13:05:23
--On Wednesday, 01 October, 2003 14:35 -0400 Keith Moore
<moore(_at_)cs(_dot_)utk(_dot_)edu> wrote:
John,
The extensions in 2428 are in wide use, and they work just
fine. I don't see any reason to change them.
Nor do I believe there is consensus that applications should
always be passing names in preference to IP addresses. And
until there is a system for assigning stable names to hosts
that are independent of any administrative domain (since hosts
often don't live in a single administrative domain), and
quickly and reliably mapping from those names to IP addresses,
the idea that applications should pass names in preference to
IP address is something that I would classify "fantasy" at
best. In particular, DNS is not sufficient to replace IP
addresses in this role.
see also
http://www.cs.utk.edu/~moore/opinions/ipv6/dns-as-endpoint-id.
html
Keith, you are starting down the path I was hoping to avoid, so
maybe my specific concern and suggestion wasn't clear. If is is
working well as is, then I withdraw even the hint of deprecating
the thing. My main objection to 2428 is not that it _permits_
addresses, but that it provides no option other than addresses
and nothing on which to hang a DNS name or other identifier if
one has one. That, it seems to me, is poor protocol design
going forward, since it implies that the next new identifier
requires yet another set of command keywords.
I suggest that it is useful, indeed important, to have a way to
express and use DNS names --and, potentially, other
identifiers-- as an alternative to addresses, if only because
they isolate the near-user interface of the applications
protocol from having to know which transport is to be used.
Unlike a number of other situations in which I would agree with
you, neither the "stable name" issue nor the independence of
administrative domain one are significant here -- we routinely
set up FTP command connections using DNS names, there are likely
to be many circumstances in which it would be equally
appropriate to set up the data connection that way, and FTP data
connections don't persist (significantly) longer than the
command connection.
We can debate --and work out-- the applicability statement that
explains when one model or the other should be used. But the
protocol should, at least, support the alterative of passing a
name.
regards,
john
I just had occasion to look again at RFC 2428, "FTP
Extensions for IPv6 and NATs", M. Allman, S. Ostermann, C.
Metz. September 1998, and to think about in the context of
the recent flame-war^H^H^H^H^H^H^H^H^H discussions about use
of IP addresses in applications. 2428 provides additional
syntax and mechanisms for FTP to deal with IPv6, with some
useful properties for NATs (useful if you believe in NATs).
It appears to provide only for addresses and does not appear
to be extensible except to the addressing formats of new
versions of IP.
It seems appropriate to ask whether 2428 should be opened and
given at least the capability of passing DNS names and maybe
some syntax that would permit clean extension to future
identifiers. In the unlikely event that there is
insufficient interest or energy to do that work, should it
be moved to historic or otherwise given a "not recommended"
status as potentially harmful and inconsistent with the
principle that applications (especially for IPv6) should be
passing names and not IP addresses?
Please consider this a fairly narrow question. I don't want
to start either the "applications level identifiers" debate
or the NAT wars again and they aren't necessary to answering
the question. On those topics, please, everyone, your
points --pro, con, or otherwise-- have been made and anyone
who is going to be convinced has been convinced. More
traffic on those subjects in the guise of responding to this
question will just convince more people that it is
impossible to carry out a technical discussion on the IETF
list.
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