Internet DRAFT - draft-tveretin-dispatch-l2tp-sdp
draft-tveretin-dispatch-l2tp-sdp
Network Working Group A. Tveretin
Internet-Draft April 10, 2017
Intended status: Standards Track
Expires: October 12, 2017
Session Description Protocol Support for Tunnels (L2TP)
draft-tveretin-dispatch-l2tp-sdp-02.txt
Abstract
This document registeres new media type (application/l2tp) to be used
with SDP, and clarifies procedure to be used by peers for L2TP
tunnels.
Status of This Memo
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Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 2
2. Possible Uses . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Opening a Connection: Normal Procedure . . . . . . . . . . . 3
3.1. The Offerer Makes an Initial Offer . . . . . . . . . . . 3
3.2. The Answerer Accepts the Offer . . . . . . . . . . . . . 3
3.3. Opening a Tunnel . . . . . . . . . . . . . . . . . . . . 3
3.4. Opening a Session . . . . . . . . . . . . . . . . . . . . 3
4. Opening a Connection: Failure . . . . . . . . . . . . . . . . 3
5. Terminating Procedures . . . . . . . . . . . . . . . . . . . 3
6. Re-opening Procedures . . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
9.1. Normative References . . . . . . . . . . . . . . . . . . 5
9.2. Informative References . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Possible Uses
This specification allows to use SIP infrastructure (including P2P)
to establish virtual private networks (VPNs). In that case, VPNs
enjoy infrastructure supported by SIP, including NAT traversal, key
exchange, and P2P networking. It also allows interworking,
eventually approaching functionality of SIP softphones to plain old
analog telephones and fax modems.
Consider the interworking between plain old analog telephone and a
SIP softphone. Alice might use her analog telephone with a fax modem
to call Bob, who is in an IP network with a softphone. Alice starts
with a voice call, a SIP gateway handles all interworking (gateway
operation is outside the scope of this specification) and routes this
call to Bob. Alice sends a fax and switches back to voice; Bob
receives the fax. Alice switches to data mode, uses text chat, sends
a file using Zmodem, and Bob receives it. Or Bob sends a file. Now
Alice starts a PPP [RFC1661] session. To maintain connectivity with
Bob, a tunnel (as of L2TP [RFC2661], PPTP [RFC2637], IPsec [RFC2401],
GPRS Tunneling Protocol) is needed.
This specification intentionally treats gateways exactly as native IP
phones. Of course, capabilites depend on actual hardware and
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software at both sides (analog telephony or ISDN, and IP) and the
gateway.
3. Opening a Connection: Normal Procedure
This specification will refer to parties as an offerer and an
answerer, as in [RFC6665].
3.1. The Offerer Makes an Initial Offer
The offerer sends an initial offer or a re-offer with an "m=" line
defined here. To introduce L2TP, the line is
m=application 1 UDP l2tp
The port number MUST be nonzero, although its actual value need not
be honoured.
3.2. The Answerer Accepts the Offer
The answerer replies with a similar "m=" line, using a port number
1701. It MAY choose another port.
3.3. Opening a Tunnel
The offerer uses known port (from the answer), and initiates a tunnel
with a usual SCCRQ message. The answerer confirmes with an SCCRP.
The offerer does SCCCN, the answerer does ZLB ACK. Parties SHOULD
open only one tunnel.
3.4. Opening a Session
The offerer starts with ICRQ, assuming the role of LAC, whether it is
a native IP terminal or a gateway. Parties SHOULD open only one
session.
4. Opening a Connection: Failure
If the answerer does not recognize or does not support "application/
l2tp", it replies as in [RFC6665].
5. Terminating Procedures
SDP dialog and L2TP tunnel and session are loosely coupled. Thus,
terminating a session does not imply closing a tunnel nor L2TP
session. Parties MUST continue to operate L2TP even if SIP (or
other) session terminates. They may tear down the tunnel, of course.
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Indeed, the party that wishes to terminate the session will do this
almost simultaneously.
Likewise, if L2TP tunnel stops (with StopCCN), parties are not
obliged to stop the dialog. Next re-offer may trigger re-opening.
6. Re-opening Procedures
In some cases e.g. roaming, or when dynamic IP address changes, a
tunnel must be reestablished. Then, a party SHOULD use the
following. Break existing L2TP tunnel, then re-offer SDP with new IP
address.
7. IANA Considerations
This memo registers an MIME or SDP media type:
o Media type name: application
o Subtype name: l2tp
o Required parameters: none
o Optional parameter: none
o Encoding considerations: This type is only defined for transfer
via RTP
o Security considerations: see RFC, section 8
o Interoperability considerations: none
o Pubished specification: RFC
o Applications which use this media type: IP telephones and
softphones, and IP-PSTN gateways
o Additional Information: Not expected to be stored in files.
o Person & e-mail address to contact for further information: Anton
Tveretin, tveretinas@yandex.ru
o Intended usage: COMMON
o Restrictions on usage: none
o Author/Change controller: The IETF
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8. Security Considerations
Due to intended usage, parties of L2TP tunnels may not have each
other credentials, and so rely on external (e.g. SIP)
authentication. Also, a description may be intercepted by third
party.
All security will be limited by a gateway, if any, rather than end-
to-end.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2661] Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn,
G., and B. Palter, "Layer Two Tunneling Protocol "L2TP"",
RFC 2661, DOI 10.17487/RFC2661, August 1999,
<http://www.rfc-editor.org/info/rfc2661>.
[RFC6665] Roach, A., "SIP-Specific Event Notification", RFC 6665,
DOI 10.17487/RFC6665, July 2012,
<http://www.rfc-editor.org/info/rfc6665>.
9.2. Informative References
[RFC1661] Simpson, W., Ed., "The Point-to-Point Protocol (PPP)",
STD 51, RFC 1661, DOI 10.17487/RFC1661, July 1994,
<http://www.rfc-editor.org/info/rfc1661>.
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, DOI 10.17487/RFC2401,
November 1998, <http://www.rfc-editor.org/info/rfc2401>.
[RFC2637] Hamzeh, K., Pall, G., Verthein, W., Taarud, J., Little,
W., and G. Zorn, "Point-to-Point Tunneling Protocol
(PPTP)", RFC 2637, DOI 10.17487/RFC2637, July 1999,
<http://www.rfc-editor.org/info/rfc2637>.
Author's Address
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Anton Tveretin
ul.Dzerzhinskogo, d. 13/1, kv.34
Surgut, HMAO-Yugra 628416
RU
Phone: +79224149328
Email: tveretinas@yandex.ru
URI: http://www.fit-rulez.narod.ru
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