> -----Original Message----- > From: JiangXingFeng [mailto:[EMAIL PROTECTED] > Sent: Thursday, January 24, 2008 6:08 PM > To: 'Dan Wing'; 'Bruce Lowekamp' > Cc: 'P2PSIP Mailing List' > Subject: RE: [P2PSIP] Choice of STUN peer or TURN peer > > > > > The TURN server is responsible for obtaining a publicly-routable > > address, and giving that address to the TURN client. The TURN > > specification, as currently written, expects the TURN server > > itself to be on a publicly-routable network ("on the Internet"). > > > > If, however, the TURN server is behind a NAT, and we want the > > TURN server to still be responsible for obtaining a > > publicly-routable IP address, you could do that. Here is a > > new technique that could be used: the TURN server could use > > STUN (or NAT-PMP or UPnP, if there is only one NAT between > > the TURN server and the Internet), and obtain a publicly- > > routable mapping: > > > > > > TURN client STUN server NAT TURN server > > | | | | > > 1. |------give me a TURN address------->|----->| > > 2. | |<--STUN Request--------| > > 3. | |-STUN Response->|----->| > > 4. |<-----here is your TURN address------------| > > > > > > Messages 2-3 are normal STUN request/response messages, and > > tell the TURN server a publicly-routable IP address and UDP > > port. The IP address and UDP port returned in in the STUN > > Response (message 3) is the TURN server's publicly-routable > > transport address, and is given to the TURN client in message > > 4. > > > > For the above message flow to work, the NAT has to be > > p2p-friendly, of course -- that is a requirement for a > > successful TURN server behind a NAT. > > > If the NAT is nested, the location of the STUN server may > fail the above the > method. For example, if the STUN server is also behind the > NAT and reflects > the inner NAT mapping, not outer most NAT mapping, to the > TURN server, the > relayed address will not be used for the TURN client to > contact with TURN > server. In order to avoid this kind of failure, stun server's location > should be learned by its clients.
Yep. That is part of the qualification a p2p-sip TURN server would have to do before it declares itself a TURN server. -d > In china, due to the lack > of the IPv4 > address, nested NAT is not a rare situation. > Comments? > > Regards! > JiangXingFeng > _______________________________________________ P2PSIP mailing list [email protected] https://www1.ietf.org/mailman/listinfo/p2psip
