Subject: RE: Guidance needed on well known ports

From: "Hallam-Baker, Phillip" <[email-masked]>
Date: Sat, 18 Mar 2006 14:09:47 -0800

The whole idea of fixed ports is broken.

The idea that there are only 1024 or even 65535 Internet applications is
broken. 

The Internet has a signalling layer, the DNS. Applications should use it.
The SRV record provides an infinitely extensible mechanism for advertising
ports.

Fixed ports do not work behind NAT. Anyone who wants to deploy IPv6 would be
well advised to pay careful attention to that restriction. SRV ports work
just fine behind a NAT.

IANA should be told to close the well known ports registry. Applications
should use DNS SRV records for service location.

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From: "Joel M. Halpern" <[email-masked]>
Date: Sat, 18 Mar 2006 18:31:05 -0500

While in general I would like to see this approach taken, this 
particular case is a perfect example of where I think one can not 
reasonably do that.  The protocol is for the purpose of configuring a 
router.  The router that needs to be configured could easily be 
between the network engineer and the DNS server.  The protocol can 
not rationally depend upon DNS (no matter how much I like the 
elegance of removing ports, using dynamic port numbers, and using dynamic DNS.)
Yes, we could invent a better way to make things work.  And maybe we should.
But Netconf should not be held up waiting for that to be developed.
Until we develop such a beast, we have to use port numbers.
Given that constraint, what guidelines ought to be used for whether a 
protocol gets a port number above or below 1024?

Yours,
Joel

At 05:09 PM 3/18/2006, Hallam-Baker, Phillip wrote:
>Content-class: urn:content-classes:message
>Content-Type: multipart/signed; protocol="application/x-pkcs7-signature";
>         micalg=SHA1; boundary="----=_NextPart_000_0011_01C64AAE.C23D25B0"
>

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From: Keith Moore <[email-masked]>
Date: Sat, 18 Mar 2006 21:09:51 -0500

> The idea that there are only 1024 or even 65535 Internet applications is

agree with you so far.

> The Internet has a signalling layer, the DNS. Applications should use it.

strongly disagree.  DNS is a huge mess.  It is slow and unreliable.  In 
practice it is often inconsistent both from one query location to 
another and with reality.

only the host knows which application is listening on which port.  if 
there is going to be a layer of indirection between service name and 
service selector, it's extremely bad design to put that layer of 
indirection external to the host that's providing the service.  (now if 
you want to argue that an architecture really needs to support clusters 
of hosts all providing the same service, I'd agree, but DNS is still not 
a good way to do this.)

> The SRV record provides an infinitely extensible mechanism for advertising

yes, and is not backward compatible with most applications.  also, for 
some reason, few new applications want to use it.

> Fixed ports do not work behind NAT. 

irrelevant.  lots of things do not work behind NAT.  NATs are inherently 
broken and cannot be fixed.  they are an architectural dead end.

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From: Joe Touch <[email-masked]>
Date: Sun, 19 Mar 2006 00:51:23 -0800

> The whole idea of fixed ports is broken.
...
> The SRV record provides an infinitely extensible mechanism for advertising

And with what port would I reach this magical DNS that would provide the
SRV record for the DNS itself?

> well advised to pay careful attention to that restriction. SRV ports work

Except that many NATs also intercept DNS requests and redirect them to
their own servers, for their own purposes, which can interfere with SRV
records (by design).

The only thing that works fine behind a NAT is what the NAT vendor wants
to work fine. Everything else is up for grabs.

Joe

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From: Stephane Bortzmeyer <[email-masked]>
Date: Mon, 20 Mar 2006 12:06:20 +0100

On Sat, Mar 18, 2006 at 02:09:47PM -0800,
 Hallam-Baker, Phillip <[email-masked]> wrote 
 a message of 163 lines which said:

> The Internet has a signalling layer, the DNS. Applications should
> use it.  The SRV record provides an infinitely extensible mechanism
> for advertising ports.

I agree here but this means we should keep at least one well-known
port, 53.
 
> IANA should be told to close the well known ports
> registry. Applications should use DNS SRV records for service
> location.

I agree with that rule for the *future* protocols. But it does not
help with current (and widely deployed) protocols. So, asking IANA to
refuse new registrations in the well-known ports registry is one
thing, shutting down the registry is another.