Re: [tae] New draft: announcing the supported transports via DNS
"Dan Wing" <dwing@cisco.com> Fri, 18 September 2009 22:54 UTC
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From: Dan Wing <dwing@cisco.com>
To: 'Bryan Ford' <bryan.ford@yale.edu>, 'Caitlin Bestler' <cait@asomi.com>
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Date: Fri, 18 Sep 2009 15:55:43 -0700
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Cc: tae@ietf.org, 'Joe Touch' <touch@ISI.EDU>
Subject: Re: [tae] New draft: announcing the supported transports via DNS
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> -----Original Message----- > From: Bryan Ford [mailto:bryan.ford@yale.edu] > Sent: Friday, September 18, 2009 1:58 PM > To: Caitlin Bestler > Cc: Dan Wing; tae@ietf.org; 'Joe Touch' > Subject: Re: [tae] New draft: announcing the supported > transports via DNS > > On Sep 18, 2009, at 3:19 PM, Caitlin Bestler wrote: > > On Sep 18, 2009, at 12:07 PM, Dan Wing wrote: > > > >> Can you enumerate those requirements, or shall we just > throw things > >> at the > >> wall? This goes back to Caitlin's post > >> <http://www.ietf.org/mail-archive/web/tae/current/msg00114.html> > >> which > >> suggested we take a step back and look at what we want. I'm all > >> for doing > >> that. This list has been too quiet, so we wrote a straw man. I > >> take it you > >> don't like the straw man because it's trying to cover the DNS use- > >> case, and > >> your use-case is IP address literals, and your use-case can incur > >> additional > >> round trip(s) to learn which transport protocols the > server supports. > > > > Any non-directory based solution is going to run the risk > of having > > an extra > > message required to setup the connection/association. That > suggests > > to me > > that the solution set should include a directory based method, I'm > > just not sure > > that DNS is appropriate for service-specific information. > > Directory-based solutions - or "out-of-band" solutions in general - > don't eliminate that risk, because as Dan just pointed out, in-band > probes are necessary anyway because a middlebox might (read: usually > will, on the IPv4 Internet) block the use of a new transport even if > the remote endpoint (truthfully) declares that it is supported. Out- > of-band communication simply cannot reliably provide the information > that is really needed on the Internet as it exists: out-of-band > information can at best serve as hints at which alternatives to try > (or to try first). > > Further, although the extra message is probably unavoidable > in certain > scenarios, in others it could potentially avoided with a bit of > cooperation between the alternative transport protocols and the > negotiation mechanism. That was the basic gist of the paper I > mentioned earlier on this list, which will appear (probably in > slightly revised form) in this year's HotNets: > > "An Efficient Cross-Layer Negotiation Protocol" > http://bford.info/pub/net/nego.pdf > > Finally, one more point in favor of in-band over out-of-band > solution > is that you only need _one_ in-band solution, No, you need two: one for UDP upgraded to some-UDP-replacement, and another for TCP upgraded to some-TCP-replacement. I have seen ideas on this mailing list for how to do in-band with TCP (using TCP options). I haven't seen any ideas for how to do in-band with UDP; perhaps because nobody cares about evolving UDP, or perhaps because there isn't an in-band solution for UDP (I expect it's the latter). -d > whereas with > out-of-band > solutions you need to define one for each directory protocol > you care > about (maybe only DNS, but that's one), PLUS a separate one for each > other protocol that exchanges IP addresses for the purpose of > setting > up transport connections (e.g., SIP, FTP, ???). Do we really > want to > have to define and deploy N different negotiation extensions, > one for > each protocol that produces IP addresses in one way or another? > > > I think the following objectives need to be met for any > probe-based > > solution: > > > > 1) Must add no additional messages when the default protocol is > > selected. > > 2) TCP must be a valid default protocol. > > 3) There may be a case for adding UDP to that set for RTTP. > > 4) It should be capable of learning when a given > client/server pair > > is blocked > > from using Transport X by some middle-box. Note: this is > > something a > > directory-based solution probably cannot do., > > Yes, these seem reasonable to me, except generalize 2 and 3 with > something to the effect of: > > When negotiating a transport for a given application X, > whatever > transport is normally the basic, "must-support" transport for > application X must be a valid default transport protocol. > > That means TCP must be a valid default protocol when negotiating a > transport for HTTP; UDP must be a valid default protocol when > negotiating a transport for RTTP; etc. > > Bryan >
- Re: [tae] New draft: announcing the supported tra… Caitlin Bestler
- [tae] New draft: announcing the supported transpo… Andrew Yourtchenko
- Re: [tae] New draft: announcing the supported tra… Melinda Shore
- Re: [tae] New draft: announcing the supported tra… Michael Welzl
- Re: [tae] New draft: announcing the supported tra… Joe Touch
- Re: [tae] New draft: announcing the supported tra… Caitlin Bestler
- Re: [tae] New draft: announcing the supported tra… Dan Wing
- Re: [tae] New draft: announcing the supported tra… Joe Touch
- Re: [tae] New draft: announcing the supported tra… Dan Wing
- Re: [tae] New draft: announcing the supported tra… Joe Touch
- Re: [tae] New draft: announcing the supported tra… Dan Wing
- Re: [tae] New draft: announcing the supported tra… Joe Touch
- Re: [tae] New draft: announcing the supported tra… Dan Wing
- Re: [tae] New draft: announcing the supported tra… Caitlin Bestler
- Re: [tae] New draft: announcing the supported tra… Caitlin Bestler
- Re: [tae] New draft: announcing the supported tra… Caitlin Bestler
- Re: [tae] New draft: announcing the supported tra… Dan Wing
- Re: [tae] New draft: announcing the supported tra… Dan Wing
- Re: [tae] New draft: announcing the supported tra… Caitlin Bestler
- Re: [tae] New draft: announcing the supported tra… Caitlin Bestler
- Re: [tae] New draft: announcing the supported tra… Michael Welzl
- Re: [tae] New draft: announcing the supported tra… Joe Touch
- Re: [tae] New draft: announcing the supported tra… Joe Touch
- Re: [tae] New draft: announcing the supported tra… Andrew Yourtchenko
- Re: [tae] New draft: announcing the supported tra… Andrew Yourtchenko
- Re: [tae] New draft: announcing the supported tra… Andrew Yourtchenko
- Re: [tae] New draft: announcing the supported tra… Joe Touch
- Re: [tae] New draft: announcing the supported tra… Andrew Yourtchenko
- Re: [tae] New draft: announcing the supported tra… Joe Touch
- Re: [tae] New draft: announcing the supported tra… Dan Wing
- Re: [tae] New draft: announcing the supported tra… Andrew Yourtchenko
- Re: [tae] New draft: announcing the supported tra… Joe Touch
- Re: [tae] New draft: announcing the supported tra… Joe Touch
- Re: [tae] New draft: announcing the supported tra… Dan Wing