TRAM P. Patil
Internet-Draft T. Reddy
Intended status: Standards Track G. Salgueiro
Expires: March 20, 2015 Cisco
M. Petit-Huguenin
Impedance Mismatch
September 16, 2014
Application Layer Protocol Negotiation (ALPN) labels for Session
Traversal Utilities for NAT (STUN) and its Usages
draft-ietf-tram-alpn-02
Abstract
Application Layer Protocol Negotiation (ALPN) labels for Session
Traversal Utilities for NAT (STUN) and its usages, such as Traversal
Using Relays around NAT (TURN) and NAT discovery, are defined in this
document to allow an application layer negotiate STUN and its usages
within the Transport Layer Security (TLS) connection. ALPN protocol
identifiers defined in this document apply to both TLS and Datagram
Transport Layer Security (DTLS).
Status of This Memo
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This Internet-Draft will expire on March 20, 2015.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. ALPN Labels . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
STUN can be securely transported using TLS-over-TCP (referred to as
TLS [RFC5246]), as specified in [RFC5389], or TLS-over-UDP (referred
to as DTLS [RFC6347]), as specified in [RFC7350].
ALPN [RFC7301] enables an endpoint to positively identify an
application protocol in TLS/DTLS and distinguish it from other TLS/
DTLS protocols. With ALPN, the client sends the list of supported
application protocols as part of the TLS/DTLS ClientHello message.
The server chooses a protocol and sends the selected protocol as part
of the TLS/DTLS ServerHello message. Application protocol
negotiation can thus be accomplished within the TLS/DTLS handshake,
without adding network round-trips.
A STUN protocol identifier and its associated usages, such as TURN,
can be used to identify the purpose of a flow without initiating a
session. This capability is useful and adds efficiency, as shown in
the following scenarios.
1. Consider an Enterprise network that deploys a TURN server in a
DeMilitarized Zone (DMZ) to audit all media sessions from inside
the Enterprise premises to any external peer. In this
deployment, an Enterprise firewall could use the TURN ALPN
identifier to detect the use of a TURN server that is outside the
Enterprise domain (i.e., a TURN server provided by an application
server, access network, etc).
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2. If a firewall is configured to block all outgoing traffic except
for TCP traffic to specific ports (e.g., 443 for HTTPS), a TURN
server listening on its default ports (3478 for TCP/UDP, 5349 for
TLS) would not be reachable. However, despite the restrictions
imposed by the firewall, a TURN server can still be reached on
the allowed HTTPS port if the TURN ALPN identifier is used to
establish usage of TURN as part of the TLS handshake.
This document defines entries in the "Application Layer Protocol
Negotiation (ALPN) Protocol IDs" registry established by [RFC7301] to
identify the STUN protocol and its usages.
2. Terminology
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].
3. ALPN Labels
The document proposes the following ALPN labels to identify the STUN
protocol and its associated usages.
'stun': Generic label to identify STUN over (D)TLS. This label
identifies the STUN protocol or any of currently defined usages
(e.g., "stun.turn", "stun.nat-discovery") as well as any future
usages that may be defined at a later date (e.g., any labels
starting with "stun.").
'stun.turn': Label to identify the specific use of STUN over (D)TLS
for TURN.
'stun.nat-discovery': Label to identify the specific use of STUN
over (D)TLS for NAT discovery.
This document does not explicitly assign ALPN labels for other usages
of STUN, such as NAT Behavior Discovery using STUN ([RFC5780]). All
such usages that do not have a dedicated label are implicitly
identified by the generic "stun" ALPN label.
4. IANA Considerations
The following entries are to be added to the "Application Layer
Protocol Negotiation (ALPN) Protocol IDs" registry established by
[RFC7301].
The "stun" label identifies STUN over (D)TLS:
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Protocol: Session Traversal Utilities for NAT (STUN)
Identification Sequence: 0x73 0x74 0x75 0x6E ("stun")
Specification: This document (RFCXXXX)
The "stun.turn" label identifies TURN usage over (D)TLS:
Protocol: Traversal Using Relays around NAT (TURN)
Identification Sequence: 0x73 0x74 0x75 0x6E 0x2E 0x74 0x75 0x72
0x6E ("stun.turn")
Specification: This document (RFCXXXX)
The "stun.nat-discovery" label identifies usage of STUN for the
purposes of NAT/behavior discovery over (D)TLS:
Protocol: NAT discovery using Session Traversal Utilities for NAT
(STUN)
Identification Sequence: 0x73 0x74 0x75 0x6E 0x2E 0x6e 0x61 0x74
0x2d 0x64 0x69 0x73 0x63 0x6f 0x76 0x65 0x72 0x79 ("stun.nat-
discovery")
Specification: This document (RFCXXXX)
5. Security Considerations
The ALPN STUN protocol identifier does not introduce any specific
security considerations beyond those detailed in the TLS ALPN
Extension specification [RFC7301]. It also does not impact security
of TLS/DTLS session establishment nor application data exchange.
6. Acknowledgements
This work benefited from the discussions and invaluable input by the
various members of the TRAM working group. These include Simon
Perrault, Paul Kyzivat, Brandon Williams and Andrew Hutton. Special
thanks to Martin Thomson and Oleg Moskalenko for their constructive
comments, suggestions, and early reviews that were critical to the
formulation and refinement of this document.
7. References
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7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
October 2008.
[RFC5780] MacDonald, D. and B. Lowekamp, "NAT Behavior Discovery
Using Session Traversal Utilities for NAT (STUN)", RFC
5780, May 2010.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, July 2014.
[RFC7350] Petit-Huguenin, M. and G. Salgueiro, "Datagram Transport
Layer Security (DTLS) as Transport for Session Traversal
Utilities for NAT (STUN)", RFC 7350, August 2014.
7.2. Informative References
[RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
Relays around NAT (TURN): Relay Extensions to Session
Traversal Utilities for NAT (STUN)", RFC 5766, April 2010.
Authors' Addresses
Prashanth Patil
Cisco Systems, Inc.
Bangalore
India
Email: praspati@cisco.com
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Tirumaleswar Reddy
Cisco Systems, Inc.
Cessna Business Park, Varthur Hobli
Sarjapur Marathalli Outer Ring Road
Bangalore, Karnataka 560103
India
Email: tireddy@cisco.com
Gonzalo Salgueiro
Cisco Systems, Inc.
7200-12 Kit Creek Road
Research Triangle Park, NC 27709
US
Email: gsalguei@cisco.com
Marc Petit-Huguenin
Impedance Mismatch
USA
Email: marc@petit-huguenin.org
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