RE: [SIP] symmetric RTP as a solution for NAT traversal
Jonathan Rosenberg <jdrosen@dynamicsoft.com> Fri, 16 March 2001 07:24 UTC
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From: Jonathan Rosenberg <jdrosen@dynamicsoft.com>
To: 'Christian Huitema' <huitema@exchange.microsoft.com>, Jonathan Rosenberg <jdrosen@dynamicsoft.com>, sip@lists.bell-labs.com, rem-conf@es.net, confctrl@isi.edu
Subject: RE: [SIP] symmetric RTP as a solution for NAT traversal
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Date: Fri, 16 Mar 2001 02:25:33 -0500
> -----Original Message----- > From: Christian Huitema [mailto:huitema@exchange.microsoft.com] > Sent: Thursday, March 15, 2001 10:22 PM > To: Jonathan Rosenberg; sip@lists.bell-labs.com; rem-conf@es.net; > confctrl@isi.edu > Subject: RE: [SIP] symmetric RTP as a solution for NAT traversal > > > Jonathan, > > Your solution is interesting, but it does not deal with the > case of two > PCs, both behind a NAT. It does. The document discusses the solution. It uses an external RTP translator. Not optimal; I recognize that. Other solutions may be possible. > Another way to solve the problem is to let the > PC who is behind a NAT learn the external mapping of the RTP > port, e.g. > that 10.0.0.9:3456 maps to 123.45.67.89:7891. There are quite > a few ways > to do that, some of which could well end up being standardized. That > would certainly be a nice complement to the symmetric RTP trick. Absolutely. There are several tractable solutions if nats conform to the UDP requirements which you have outlined, Christian, in: http://search.ietf.org/internet-drafts/draft-huitema-natreq4udp-00.txt > > However, there is a slight problem. We cannot assume that > NATs are aware > of RTP's requirement for "port pairs", an even port for RTP, the next > port for RTCP. We may well learn that port 3456 maps to > 123.45.67.89:7891, and port 3457 maps to 123.45.67.89:9872. Now, if we > intend to open the SDP spec and create attributes for the "symmetric > RTP", we should perhaps also create an attribute specifying the RTCP > port, when that port is not equal to RTP+1. If we do some kind of solution where the external entity tells both UAs their public addresses, then yes, this will be needed. > > A mild objection to the symmetric RTP is the risk of session > hijacking. > Arguably, that is a risk you can assume if the alternative is > no session > at all, but you should still consider it... How does symmetric RTP create a risk of hijacking? -Jonathan R. --- Jonathan D. Rosenberg 72 Eagle Rock Ave. Chief Scientist First Floor dynamicsoft East Hanover, NJ 07936 jdrosen@dynamicsoft.com FAX: (973) 952-5050 http://www.cs.columbia.edu/~jdrosen PHONE: (973) 952-5000 http://www.dynamicsoft.com _______________________________________________ This list is for continuing development of the SIP protocol. The sip-implementor's list is the place to discuss implementation, and to receive advice on understanding existing sip. To subscribe to it, send mail to sip-implementors-request@cs.columbia.edu with "subscribe" in the body.
- RE: [SIP] symmetric RTP as a solution for NAT tra… Christian Huitema
- RE: [SIP] symmetric RTP as a solution for NAT tra… Michael Thomas
- RE: [SIP] symmetric RTP as a solution for NAT tra… Jonathan Rosenberg
- RE: [SIP] symmetric RTP as a solution for NAT tra… Michael Thomas
- RE: [SIP] symmetric RTP as a solution for NAT tra… Jonathan Rosenberg
- [SIP] RE: symmetric RTP as a solution for NAT tra… Jonathan Rosenberg
- RE: [SIP] symmetric RTP as a solution for NAT tra… Jonathan Rosenberg
- [SIP] symmetric RTP as a solution for NAT travers… Michael Thomas
- [SIP] Re: symmetric RTP as a solution for NAT tra… Dirk Kutscher
- RE: [SIP] symmetric RTP as a solution for NAT tra… Christian Huitema
- Re: [SIP] symmetric RTP as a solution for NAT tra… Dean Willis
- RE: [SIP] symmetric RTP as a solution for NAT tra… Kevin Marks
- [SIP] symmetric RTP as a solution for NAT travers… Jonathan Rosenberg
- RE: [SIP] symmetric RTP as a solution for NAT tra… Jonathan Rosenberg
- RE: [SIP] symmetric RTP as a solution for NAT tra… Jonathan Rosenberg
- RE: [SIP] symmetric RTP as a solution for NAT tra… shh