Subject: [pcp] Using dynamically assigned port numbers with static URLs

From: Masataka Ohta <[email-masked]>
Date: Mon, 31 Oct 2011 18:07:12 +0900

Hi,

Are there anyone who are interested in application aspect
of port control, here?

That is, if a server is dynamically assigned a global port
number through PCP, it should somehow be publicly advertised
to make the server reachable from the rest of the world.

But, it is not possible to modify old port numbers encoded
in URLs of clients' bookmarks.

Thus, it is necessary to have a mechanism to map a static
URLs to dynamically assigned IP addresses and port numbers.

Dynamic update on DNS address records can change IP addresses
of URLs but there is no well defined way to do so with port
numbers.

So, I wrote an ID "Using DNS SRV RRs with URLs":

	http://tools.ietf.org/html/draft-ohta-urlsrv-00.txt

Comments, which may be directed to dnsext list, are welcome.

					Masataka Ohta

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From: Keith Moore <[email-masked]>
Date: Mon, 31 Oct 2011 08:09:23 -0400

I think this is a Very Bad Idea.

IPv4 is at EOL.  Port mapping NATs should also be considered at EOL.  I understand that the motivation for creating PCP was LSNs and the loss of UPnP/NAT-PMP capability, but PCP is useful even without port-mapping NATs.  We should not be destroying a valuable capability to explicitly specify port numbers and have those literal port numbers mean what they say, just because of LSNs.

Keith

On Oct 31, 2011, at 5:07 AM, Masataka Ohta wrote:

> _______________________________________________
> pcp mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/pcp

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From: Francis Dupont <[email-masked]>
Date: Mon, 31 Oct 2011 13:09:13 +0100

In your previous mail you wrote:

=> there is some indications in the base draft, even only
in non-normative sections (this is out of scope of the PCP WG)
and more DNS SD than SRV oriented.

=> SRV and DNS SD...

   
   
=> IMHO it is more dnsop than dnsext as you propose a clever
use of SRV RRs, not a new protocol/RR/etc.

I have a concern about using (dynamic) DNS is this context:
DNS answers are cached, in fact even with TTL=0 by most applications,
so it doesn't survive a CGN address or port renumbering from a reboot.

Note this is not an issue for the now traditional DHCP+DDNS used
for nomadism because in that context the nomad server releases/
deregisters before being shutdowned and no longer available for
a delay greater than the DNS lifetime, i.e., in the rare cases
a nomad computer provides a service this can be done in a
secure way. This is not the case for a server behind a CGN
which doesn't enforce mapping stability using for instance
stable storage.

Regards

[email-masked]