Internet DRAFT - draft-wing-tram-turn-mobility
draft-wing-tram-turn-mobility
TRAM D. Wing
Internet-Draft P. Patil
Intended status: Standards Track T. Reddy
Expires: November 7, 2015 P. Martinsen
Cisco
May 6, 2015
Mobility with TURN
draft-wing-tram-turn-mobility-03
Abstract
It is desirable to minimize traffic disruption caused by changing IP
address during a mobility event. One mechanism to minimize
disruption is to expose a shorter network path to the mobility event
so only the local network elements are aware of the changed IP
address but the remote peer is unaware of the changed IP address.
This draft provides such an IP address mobility solution using
Traversal Using Relays around NAT (TURN). This is achieved by
allowing a client to retain an allocation on the TURN server when the
IP address of the client changes.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on November 7, 2015.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Notational Conventions . . . . . . . . . . . . . . . . . . . 3
3. Mobility using TURN . . . . . . . . . . . . . . . . . . . . . 3
3.1. Creating an Allocation . . . . . . . . . . . . . . . . . 4
3.1.1. Sending an Allocate Request . . . . . . . . . . . . . 4
3.1.2. Receiving an Allocate Request . . . . . . . . . . . . 5
3.1.3. Receiving an Allocate Success Response . . . . . . . 5
3.1.4. Receiving an Allocate Error Response . . . . . . . . 5
3.2. Refreshing an Allocation . . . . . . . . . . . . . . . . 6
3.2.1. Sending a Refresh Request . . . . . . . . . . . . . . 6
3.2.2. Receiving a Refresh Request . . . . . . . . . . . . . 6
3.2.3. Receiving a Refresh Response . . . . . . . . . . . . 7
3.3. New STUN Attribute MOBILITY-TICKET . . . . . . . . . . . 7
3.4. New STUN Error Response Code . . . . . . . . . . . . . . 7
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 8
5.1. open-sys . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. Example ticket construction . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
When moving between networks, the endpoint's IP address can change or
(due to NAT) the endpoint's public IP address can change. Such a
change of IP address breaks upper layer protocols such as TCP and
RTP. Various techniques exist to prevent this breakage, all tied to
making the endpoint's IP address static (e.g., Mobile IP, Proxy
Mobile IP, LISP). Other techniques exist, which make the change in
IP address agnostic to the upper layer protocol (e.g., SCTP). The
mechanism described in this document are in that last category.
A Traversal Using Relays around NAT (TURN) [RFC5766] server relays
media packets and is used for a variety of purposes, including
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overcoming NAT and firewall traversal issues. The existing TURN
specification does not permit a TURN client to reuse an allocation
across client IP address changes. Due to this, when the IP address
of the client changes, the TURN client has to request for a new
allocation, create permissions for the remote peer, create channels
etc. In addition the client has to re-establish communication with
its SIP server, send an updated offer to the remote peer conveying
the new relayed candidate address, remote side has to regather all
candidates and signal them to the client and then the endpoints have
to perform Interactive Connectivity Establishment (ICE) [RFC5245]
connectivity checks. If ICE continious nomination procedure
[I-D.uberti-mmusic-nombis] is used then new relayed candidate address
would have to be tricked [I-D.ietf-mmusic-trickle-ice] and ICE
connectivity checks have to be performed by the endpoints to nominate
pairs that will be selected by ICE.
This specification describes a mechanism to seamlessly reuse
allocations across client IP address changes without any of the
hassles described above. A critical benefit of this technique is
that the remote peer does not have to support mobility, or deal with
any of the address changes. The client, that is subject to IP
address changes, does all the work. The mobility technique works
across and between network types (e.g., between 3G and wired Internet
access), so long as the client can still access the TURN server. The
technique should also work seamlessly when (D)TLS is used as a
transport protocol for STUN. When there is a change in IP address,
the client uses (D)TLS Session Resumption without Server-Side State
as described in [RFC5077] to resume secure communication with the
TURN server, using the changed client IP address.
2. Notational Conventions
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].
This note uses terminology defined in [RFC5245], and the following
additional terminology:
3. Mobility using TURN
To achieve mobility, a TURN client should be able to retain an
allocation on the TURN server across changes in the client IP address
as a consequence of movement to other networks.
When the client sends the initial Allocate request to the TURN
server, it will include a new STUN attribute MOBILITY-TICKET (with
zero length value), which indicates that the client is capable of
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mobility and desires a ticket. The TURN server provisions a ticket
that is sent inside the new STUN attribute MOBILITY-TICKET in the
Allocate Success response to the client. The ticket will be used by
the client when it wants to refresh the allocation but with a new
client IP address and port. This ensures that an allocation can only
be refreshed by the same client that allocated relayed transport
address. When a client's IP address changes due to mobility, it
presents the previously obtained ticket in a Refresh Request to the
TURN server. If the ticket is found to be valid, the TURN server
will retain the same relayed address/port for the new IP address/port
allowing the client to continue using previous channel bindings --
thus, the TURN client does not need to obtain new channel bindings.
Any data from external peer will be delivered by the TURN server to
this new IP address/port of the client. The TURN client will
continue to send application data to its peers using the previously
allocated channelBind Requests.
TURN TURN Peer
client server A
|-- Allocate request --------------->| |
| + MOBILITY-TICKET (length=0) | |
| | |
|<--------------- Allocate failure --| |
| (401 Unauthorized) | |
| | |
|-- Allocate request --------------->| |
| + MOBILITY-TICKET (length=0) | |
| | |
|<---------- Allocate success resp --| |
| + MOBILITY-TICKET | |
... ... ...
(changes IP address)
| | |
|-- Refresh request ---------------->| |
| + MOBILITY-TICKET | |
| | |
|<----------- Refresh success resp --| |
| + MOBILITY-TICKET | |
| | |
3.1. Creating an Allocation
3.1.1. Sending an Allocate Request
In addition to the process described in Section 6.1 of [RFC5766], the
client includes the MOBILITY-TICKET attribute with length 0. This
indicates the client is a mobile node and wants a ticket.
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3.1.2. Receiving an Allocate Request
In addition to the process described in Section 6.2 of [RFC5766], the
server does the following:
If the MOBILITY-TICKET attribute is included, and has length zero,
but TURN session mobility is forbidden by local policy, the server
MUST reject the request with the new Mobility Forbidden error code.
If the MOBILITY-TICKET attribute is included and has non-zero length
then the server MUST generate an error response with an error code of
400 (Bad Request). Following the rules specified in [RFC5389], if
the server does not understand the MOBILITY-TICKET attribute, it
ignores the attribute.
If the server can successfully process the request create an
allocation, the server replies with a success response that includes
a STUN MOBILITY-TICKET attribute. TURN server can store system
internal data into the ticket that is encrypted by a key known only
to the TURN server and sends the ticket in the STUN MOBILITY-TICKET
attribute as part of Allocate success response. The ticket is opaque
to the client, so the structure is not subject to interoperability
concerns, and implementations may diverge from this format. An
example for ticket construction is discussed in Appendix A. The
client could be roaming across networks with different path MTU and
from one address family to another (e.g. IPv6 to IPv4). The TURN
server to support mobility must assume that the path MTU is unknown
and the STUN message over IPv4 needs to be less than 548 bytes to
avoid UDP fragmentation(Section 7.1 of [RFC5389]), it MUST ensure
that the ticket length is restricted to fit within the 548 byte STUN
message size. Clients MUST NOT examine the ticket under the
assumption that it complies with this document.
3.1.3. Receiving an Allocate Success Response
In addition to the process described in Section 6.3 of [RFC5766], the
client will store the MOBILITY-TICKET attribute, if present, from the
response. This attribute will be presented by the client to the
server during a subsequent Refresh request to aid mobility.
3.1.4. Receiving an Allocate Error Response
If the client receives an Allocate error response with error code TBD
(Mobility Forbidden), the error is processed as follows:
o TBD (Mobility Forbidden): The request is valid, but the server is
refusing to perform it, likely due to administrative restrictions.
The client considers the current transaction as having failed. The
client MAY notify the user or operator and SHOULD NOT retry the same
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request with this server until it believes the problem has been
fixed.
All other error responses must be handled as described in [RFC5766].
3.2. Refreshing an Allocation
3.2.1. Sending a Refresh Request
If a client wants to refresh an existing allocation and update its
time-to-expiry or delete an existing allocation, it will send a
Refresh Request as described in Section 7.1 of [RFC5766]. If the
client wants to retain the existing allocation in case of IP change,
it will include the MOBILITY-TICKET attribute received in the
Allocate Success response. If a Refresh transaction was previously
made, the MOBILITY-TICKET attribute received in the Refresh Success
response of the transaction must be used.
3.2.2. Receiving a Refresh Request
In addition to the process described in Section 7.2 of [RFC5766], the
server does the following:
If the STUN MOBILITY-TICKET attribute is included in the Refresh
Request then the server will not retrieve the 5-tuple from the packet
to identify an associated allocation. Instead the TURN server will
decrypt the received ticket, verify the ticket's validity and
retrieve the 5-tuple allocation using the ticket. If this 5-tuple
obtained does not identify an existing allocation then the server
MUST reject the request with an error.
If the source IP address and port of the Refresh Request is different
from the stored 5-tuple allocation, the TURN server proceeds with
MESSAGE-INTEGRITY validation to identify the that it is the same user
which had previously created the TURN allocation. If the above
checks are not successful then server MUST reject the request with a
441 (Wrong Credentials) error.
If all of the above checks pass, the TURN server understands that the
client has moved to a new network and acquired a new IP address. The
source IP address of the request could either be the host transport
address or server-reflexive transport address. The server then
updates it's 5-tuple with the new client IP address and port. TURN
server calculates the ticket with the new 5-tuple and sends the new
ticket in the STUN MOBILITY-TICKET attribute as part of Refresh
Success response. The old ticket can only be used for the purposes
of retransmission. If the client wants to refresh its allocation
with a new server-reflexive transport address, it MUST use the new
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ticket. If the TURN server has not received a Refresh Request with
STUN MOBILITY-TICKET attribute but receives Send indications or
ChannelData messages from a client, the TURN server may discard or
queue those Send indications or ChannelData messages (at its
discretion). Thus, it is RECOMMENDED that the client avoid
transmitting a Send indication or ChannelData message until it has
received an acknowledgement for the Refresh Request with STUN
MOBILITY-TICKET attribute.
To accommodate for loss of Refresh responses, a server must retain
the old STUN MOBILITY-TICKET attribute for a period of at least 30
seconds to be able recognize a retransmission of Refresh request with
the old STUN MOBILITY-TICKET attribute from the client.
3.2.3. Receiving a Refresh Response
In addition to the process described in Section 7.3 of [RFC5766], the
client will store the MOBILITY-TICKET attribute, if present, from the
response. This attribute will be presented by the client to the
server during a subsequent Refresh Request to aid mobility.
3.3. New STUN Attribute MOBILITY-TICKET
This attribute is used to retain an Allocation on the TURN server.
It is exchanged between the client and server to aid mobility. The
value of MOBILITY-TICKET is encrypted and is of variable-length.
3.4. New STUN Error Response Code
This document defines the following new error response code:
Mobility Forbidden: Mobility request was valid but cannot be
performed due to administrative or similar restrictions.
4. IANA Considerations
IANA is requested to add the following attributes to the STUN
attribute registry [iana-stun],
o MOBILITY-TICKET (0x802E, in the comprehension-optional range)
and to add a new STUN error code "Mobility Forbidden" with the value
405 to the STUN Error Codes registry [iana-stun].
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5. Implementation Status
[Note to RFC Editor: Please remove this section and reference to
[RFC6982] prior to publication.]
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC6982].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC6982], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
5.1. open-sys
Organization: This is a public project, the full list of authors
and contributors here: http://turnserver.open-sys.org/downloads/
AUTHORS
Description: A mature open-source TURN server specs implementation
(RFC 5766, RFC 6062, RFC 6156, etc) designed for high-performance
applications, especially geared for WebRTC.
Implementation: http://code.google.com/p/rfc5766-turn-server/
Level of maturity: The Mobile ICE feature implementation can be
qualified as "production" - it is well tested and fully
implemented, but not widely used, yet..
Coverage: Fully implements MICE with TURN protocol.
Licensing: BSD: http://turnserver.open-sys.org/downloads/LICENSE
Implementation experience: MICE implementation is somewhat
challenging for a multi-threaded performance-oriented application
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(because the mobile ticket information must be shared between the
threads) but it is doable.
Contact: Oleg Moskalenko <mom040267@gmail.com>.
6. Security Considerations
TURN server MUST use strong encryption and integrity protection for
the ticket to prevent an attacker from using a brute force mechanism
to obtain the ticket's contents or refreshing allocations. The
ticket MUST be constructed such that it has strong entropy to ensure
nothing can be gleaned by looking at the ticket alone.
Security considerations described in [RFC5766] are also applicable to
this mechanism.
7. Acknowledgements
Thanks to Alfred Heggestad, Lishitao, Sujing Zhou, Martin Thomson,
Emil Ivov, Oleg Moskalenko and Brandon Williams for review and
comments.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
"Transport Layer Security (TLS) Session Resumption without
Server-Side State", RFC 5077, January 2008.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245, April
2010.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
October 2008.
[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.
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8.2. Informative References
[I-D.ietf-mmusic-trickle-ice]
Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE:
Incremental Provisioning of Candidates for the Interactive
Connectivity Establishment (ICE) Protocol", draft-ietf-
mmusic-trickle-ice-02 (work in progress), January 2015.
[I-D.uberti-mmusic-nombis]
Uberti, J. and J. Lennox, "Improvements to ICE Candidate
Nomination", draft-uberti-mmusic-nombis-00 (work in
progress), March 2015.
[RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", RFC 6982, July
2013.
[iana-stun]
IANA, , "IANA: STUN Attributes", April 2011,
<http://www.iana.org/assignments/stun-parameters/stun-pa
rameters.xml>.
Appendix A. Example ticket construction
The TURN server uses two different keys: one 128-bit key for Advance
Encryption Standard (AES) in Cipher Block Chaining (CBC) mode
(AES_128_CBC) and 256-bit key for HMAC-SHA-256-128 for integrity
protection. The ticket can be structured as follows:
struct {
opaque key_name[16];
opaque iv[16];
opaque state<0..2^16-1>;
opaque mac[16];
} ticket;
Figure 1: Ticket Format
Here, key_name serves to identify a particular set of keys used to
protect the ticket. It enables the TURN server to easily recognize
tickets it has issued. The key_name should be randomly generated to
avoid collisions between servers. One possibility is to generate new
random keys and key_name every time the server is started.
The TURN state information (self-contained or handle) in
encrypted_state is encrypted using 128-bit AES in CBC mode with the
given IV. The MAC is calculated using HMAC-SHA-256-128 over key_name
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(16 octets)and IV (16 octets), followed by the length of the
encrypted_state field (2 octets) and its contents (variable length).
Authors' Addresses
Dan Wing
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, California 95134
USA
Email: dwing@cisco.com
Prashanth Patil
Cisco Systems, Inc.
Bangalore
India
Email: praspati@cisco.com
Tirumaleswar Reddy
Cisco Systems, Inc.
Cessna Business Park, Varthur Hobli
Sarjapur Marathalli Outer Ring Road
Bangalore, Karnataka 560103
India
Email: tireddy@cisco.com
Paal-Erik Martinsen
Cisco Systems, Inc.
Philip Pedersens vei 22
Lysaker, Akershus 1325
Norway
Email: palmarti@cisco.com
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