Re: [tae] New draft: announcing the supported transports via DNS

["Dan Wing" <[e-mail]>]

> Dan Wing wrote:
> >> As you note, addresses are sometimes used for non-human 
> >> purposes, and
> >> with IPv6 they could be created on the fly - I wouldn't want 
> >> to have to
> >> wait to register them in the DNS vs exchanging them in-band.
> > 
> > So, when you exchange them (in whatever 
> > application-specific protocol 
> > you're using to exchange those addresses, e.g., SDP for RTSP, SAP, 
> > and SIP) using that application-specific protocol is the best place 
> > to indicate which transport protocol is supported on the host. 
> 
> I might want to say "here, use this address, but use whatever 
> transport the other end wants to use for reliable object 
> transfer", which wouldn't have the information available to 
> the protocol that indicates the address.

I don't understand; if you have an existing protocol to send
an IPv4 or IPv6 address around, it can be extended to include
a port (as most application developers have found necessary,
as we can't have more than one HTTP server listening on port
80 behind an in-home NAT), and it can likewise be extended to
say "TCP=yes, SCTP=yes, DCCP=no".

You're saying such an extension is not possible / reasonable?

> > This
> > is exactly how ICE extended SDP to allow indicating other transport
> > protocols, http://tools.ietf.org/html/draft-ietf-mmusic-ice-19.
> > The GROBJ BoF is where we're hoping to provide similar guidance to 
> > application developers who are referring IPv6/IPv4 addresses 
> > around.
> > 
> > 
> > Absent such an application-specific protocol to exchange addresses
> > we have the Internet's protocol to exchange addresses:  DNS.
> 
> I don't want to use the DNS - I gave the other end an address, not a
> name. The negotiation of how to talk between two endpoints is not an
> endpoint alias issue - and the latter is what the DNS provides.

I agree that protocols that exchange IP address literals should not,
and can not, use DNS.  My suggestion (above) for those protocols is
that the protocol that is carrying the IP address literal also 
carry which transport protocol is supported by the server, rather
than merely defaulting to UDP or defaulting to TCP.

I want to use DNS for protocols that are already using DNS.

I also don't want to use TCP to learn the transport protocol, 
because I may want to negotiate from UDP to DCCP, or negotiate
from UDP to SCTP.


Do you have a proposal you could share on the mailing list or
in an I-D?

-d