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P2PSIP                                                       C. Jennings
Internet-Draft                                                     Cisco
Intended status: Standards Track                             B. Lowekamp
Expires: October 29, 2016                                          Skype
                                                             E. Rescorla
                                                              RTFM, Inc.
                                                                S. Baset
                                                          H. Schulzrinne
                                                     Columbia University
                                                         T. Schmidt, Ed.
                                                             HAW Hamburg
                                                          April 27, 2016


                         A SIP Usage for RELOAD
                        draft-ietf-p2psip-sip-21

Abstract

   This document defines a SIP Usage for REsource LOcation And Discovery
   (RELOAD).  The SIP Usage provides the functionality of a SIP proxy or
   registrar in a fully-distributed system and includes a lookup service
   for Address of Records (AORs) stored in the overlay.  It also defines
   Globally Routable User Agent URIs (GRUUs) that allow the
   registrations to map an AOR to a specific node reachable through the
   overlay.  After such initial contact of a peer, the RELOAD AppAttach
   method is used to establish a direct connection between nodes through
   which SIP messages are exchanged.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 29, 2016.






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Copyright Notice

   Copyright (c) 2016 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Registering AORs in the Overlay . . . . . . . . . . . . . . .   6
     3.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  Data Structure  . . . . . . . . . . . . . . . . . . . . .   6
     3.3.  Access Control  . . . . . . . . . . . . . . . . . . . . .   8
     3.4.  Overlay Configuration Document Extension  . . . . . . . .   9
   4.  Looking up an AOR . . . . . . . . . . . . . . . . . . . . . .  10
     4.1.  Finding a Route to an AOR . . . . . . . . . . . . . . . .  10
     4.2.  Resolving an AOR  . . . . . . . . . . . . . . . . . . . .  11
   5.  Forming a Direct Connection . . . . . . . . . . . . . . . . .  11
     5.1.  Setting Up a Connection . . . . . . . . . . . . . . . . .  11
     5.2.  Keeping a Connection Alive  . . . . . . . . . . . . . . .  12
   6.  Using GRUUs . . . . . . . . . . . . . . . . . . . . . . . . .  12
   7.  SIP-REGISTRATION Kind Definition  . . . . . . . . . . . . . .  13
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
     8.1.  RELOAD-Specific Issues  . . . . . . . . . . . . . . . . .  14
     8.2.  SIP-Specific Issues . . . . . . . . . . . . . . . . . . .  14
       8.2.1.  Fork Explosion  . . . . . . . . . . . . . . . . . . .  14



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       8.2.2.  Malicious Retargeting . . . . . . . . . . . . . . . .  15
       8.2.3.  Misuse of AORs  . . . . . . . . . . . . . . . . . . .  15
       8.2.4.  Privacy Issues  . . . . . . . . . . . . . . . . . . .  15
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
     9.1.  Data Kind-ID  . . . . . . . . . . . . . . . . . . . . . .  15
     9.2.  XML Name Space Registration . . . . . . . . . . . . . . .  16
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  16
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     11.2.  Informative References . . . . . . . . . . . . . . . . .  18
   Appendix A.  Third Party Registration . . . . . . . . . . . . . .  18
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  18
     B.1.  Changes since draft-ietf-p2psip-sip-09  . . . . . . . . .  19
     B.2.  Changes since draft-ietf-p2psip-sip-08  . . . . . . . . .  19
     B.3.  Changes since draft-ietf-p2psip-sip-07  . . . . . . . . .  19
     B.4.  Changes since draft-ietf-p2psip-sip-06  . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction

   REsource LOcation And Discovery (RELOAD) [RFC6940] specifies a peer-
   to-peer (P2P) signaling protocol for the general use on the Internet.
   This document defines a SIP Usage of RELOAD that allows SIP [RFC3261]
   user agents (UAs) to establish peer-to-peer SIP (or SIPS) sessions
   without the requirement for permanent proxy or registration servers,
   e.g., a fully distributed telephony service.  This service
   transparently supports SIP addressing including telephone numbers.
   In such a network, the RELOAD overlay itself performs the
   registration and rendezvous functions ordinarily associated with such
   servers.

   The SIP Usage involves two basic functions.

   Registration:  SIP UAs can use the RELOAD data storage functionality
      to store a mapping from their address-of-record (AOR) to their
      Node-ID in the overlay, and to retrieve the Node-ID of other UAs.

   Rendezvous:  Once a SIP UA has identified the Node-ID for an AOR it
      wishes to call, it can use the RELOAD message routing system to
      set up a direct connection for exchanging SIP messages.

   Mappings are stored in the SipRegistration Resource Record defined in
   this document.  All operations required to perform a SIP registration
   or rendezvous are standard RELOAD protocol methods.

   For example, Bob registers his AOR, "bob@dht.example.com", for his
   Node-ID "1234".  When Alice wants to call Bob, she queries the
   overlay for "bob@dht.example.com" and receives Node-ID "1234" in



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   return.  She then uses the overlay routing to establish a direct
   connection with Bob and can directly transmit a standard SIP INVITE.
   In detail, this works along the following steps.

   1.  Bob, operating Node-ID "1234", stores a mapping from his AOR to
       his Node-ID in the overlay by applying a Store request for
       "bob@dht.example.com -> 1234".

   2.  Alice, operating Node-ID "5678", decides to call Bob. She
       retrieves Node-ID "1234" by performing a Fetch request on
       "bob@dht.example.com".

   3.  Alice uses the overlay to route an AppAttach message to Bob's
       peer (ID "1234").  Bob responds with his own AppAttach and they
       set up a direct connection, as shown in Figure 1.  Note that
       mutual Interactive Connectivity Establishment (ICE) checks are
       invoked automatically from AppAttach message exchange.

                        Overlay
   Alice       Peer1     ...          PeerN      Bob
   (5678)                                     (1234)
   -------------------------------------------------
   AppAttach ->
               AppAttach ->
                         AppAttach ->
                                     AppAttach ->
                                        <- AppAttach
                               <- AppAttach
                    <- AppAttach
        <- AppAttach

   <------------------ ICE Checks ----------------->
   INVITE ----------------------------------------->
   <--------------------------------------------- OK
   ACK -------------------------------------------->
   <------------ ICE Checks for media ------------->
   <-------------------- RTP ---------------------->


      Figure 1: Connection setup in P2P SIP using the RELOAD overlay

   It is important to note that here the only role of RELOAD is to set
   up the direct SIP connection between Alice and Bob. As soon as the
   ICE checks complete and the connection is established, ordinary SIP
   or SIPS is used.  In particular, the establishment of the media
   channel for a phone call happens via the usual SIP mechanisms, and
   RELOAD is not involved.  Media never traverses the overlay.  After




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   the successful exchange of SIP messages, call peers run ICE
   connectivity checks for media.

   In addition to mappings from AORs to Node-IDs, the SIP Usage also
   allows mappings from AORs to other AORs.  This enables an indirection
   useful for call forwarding.  For instance, if Bob wants his phone
   calls temporarily forwarded to Charlie, he can store the mapping
   "bob@dht.example.com -> charlie@dht.example.com".  When Alice wants
   to call Bob, she retrieves this mapping and can then fetch Charlie's
   AOR to retrieve his Node-ID.  These mechanisms are described in
   Section 3.

   Alternatively, Globally Routable User Agent URIs (GRUUs) [RFC5627]
   can be used for directly accessing peers.  They are handled via a
   separate mechanism, as described in Section 6.

   The SIP Usage for RELOAD addresses a fully distributed deployment of
   session-based services among overlay peers.  This RELOAD usage may be
   relevant in a variety of environments, including a highly regulated
   environment of a "single provider" that admits parties using AORs
   with domains from controlled namespace(s) only, or an open, multi-
   party infrastructure that liberally allows a registration and
   rendezvous for various or any domain namespace.  It is noteworthy in
   this context that - in contrast to regular SIP - domain names play no
   role in routing to a proxy server.  Once connectivity to an overlay
   is given, any name registration can be technically processed.

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 RFC 2119 [RFC2119].

   We use the terminology and definitions from Concepts and Terminology
   for Peer to Peer SIP [I-D.ietf-p2psip-concepts] and the RELOAD Base
   Protocol [RFC6940] extensively in this document.

   In addition, term definitions from SIP [RFC3261] apply to this memo.
   The term AOR is the SIP "Address of Record" used to identify a user
   in SIP.  For example, alice@example.com could be the AOR for Alice.
   For the purposes of this specification, an AOR is considered not to
   include the scheme (e.g. sip:) as the AOR needs to match the
   rfc822Name in the X509v3 certificates [RFC5280].  It is worth noting
   that SIP and SIPS are distinguished in P2PSIP by the Application-ID.







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3.  Registering AORs in the Overlay

3.1.  Overview

   In ordinary SIP, a UA registers the user's AOR and its network
   location with a registrar.  In RELOAD, this registrar function is
   provided by the overlay as a whole.  To register its location, a
   RELOAD peer stores a SipRegistration Resource Record under its own
   AOR using the SIP-REGISTRATION Kind, which is formally defined in
   Section 7.  Note that the registration lifetime known from the
   regular SIP REGISTER method is inherited from the lifetime attribute
   of the basic RELOAD StoredData structure (see Section 7 in
   [RFC6940]).

   A RELOAD overlay MAY restrict the storage of AORs.  Namespaces (i.e.,
   the right hand side of the AOR) that are supported for registration
   and lookup can be configured for each RELOAD deployment as described
   in Section 3.4.

   As a simple example, consider Alice with AOR "alice@dht.example.org"
   at Node-ID "1234".  She might store the mapping
   "alice@dht.example.org -> 1234" telling anyone who wants to call her
   to contact node "1234".

   RELOAD peers can store two kinds of SIP mappings,

   o  from an AOR to a destination list (a single Node-ID is just a
      trivial destination list), or

   o  from an AOR to another AOR.

   The meaning of the first kind of mapping is "in order to contact me,
   form a connection with this peer."  The meaning of the second kind of
   mapping is "in order to contact me, dereference this AOR".  The
   latter allows for forwarding.  For instance, if Alice wants her calls
   to be forwarded to her secretary, Sam, she might insert the following
   mapping "alice@dht.example.org -> sam@dht.example.org".

3.2.  Data Structure

   This section defines the SipRegistration Resource Record as follows:










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          enum { sip_registration_uri(1), sip_registration_route(2),
             (255) } SipRegistrationType;

          select (SipRegistration.type) {
            case sip_registration_uri:
              opaque               uri<0..2^16-1>;

            case sip_registration_route:
              opaque               contact_prefs<0..2^16-1>;
              Destination          destination_list<0..2^16-1>;

            /* This type can be extended */

          } SipRegistrationData;

          struct {
             SipRegistrationType   type;
             uint16                length;
             SipRegistrationData   data;
         } SipRegistration;



   The contents of the SipRegistration Resource Record are:



   type

      the type of the registration



   length

      the length of the rest of the PDU



   data

      the registration data

   o  If the registration is of type "sip_registration_uri", then the
      contents are an opaque string containing the AOR.






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   o  If the registration is of type "sip_registration_route", then the
      contents are an opaque string containing the registrant's contact
      preferences and a destination list for the peer.

   The callee expresses its capabilities within the contact preferences
   as specified in [RFC3840].  It encodes a media feature set comprised
   of its capabilities as a contact predicate, i.e., a string of feature
   parameters that appear as part of the Contact header field.  Feature
   parameters are derived from the media feature set syntax of [RFC2533]
   (see also [RFC2738]) as described in [RFC3840].

   This encoding covers all SIP User Agent capabilities, as defined in
   [RFC3840] and registered in the SIP feature tag registration tree.
   In particular, a callee can indicate that it prefers contact via a
   particular SIP scheme - SIP or SIPS - by using one of the following
   contact_prefs attribute:

         (sip.schemes=SIP)
         (sip.schemes=SIPS)

   RELOAD explicitly supports multiple registrations for a single AOR.
   The registrations are stored in a Dictionary with Node-IDs as the
   dictionary keys.  Consider, for instance, the case where Alice has
   two peers:

   o  her desk phone (1234)

   o  her cell phone (5678)

   Alice might store the following in the overlay at resource
   "alice@dht.example.com".

   o  A SipRegistration of type "sip_registration_route" with dictionary
      key "1234" and value "1234".

   o  A SipRegistration of type "sip_registration_route" with dictionary
      key "5678" and value "5678".

   Note that this structure explicitly allows one Node-ID to forward to
   another Node-ID.  For instance, Alice could set calls to her desk
   phone to ring at her cell phone by storing a SipRegistration of type
   "sip_registration_route" with dictionary key "1234" and value "5678".

3.3.  Access Control

   In order to prevent hijacking or other misuse, registrations are
   subject to access control rules.  Two kinds of restrictions apply:




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   o  A Store is permitted only for AORs with domain names that fall
      into the namespaces supported by the RELOAD overlay instance.

   o  Storing requests are performed according to the USER-NODE-MATCH
      access control policy of RELOAD.

   Before issuing a Store request to the overlay, any peer SHOULD verify
   that the AOR of the request is a valid Resource Name with respect to
   its domain name and the namespaces defined in the overlay
   configuration document (see Section 3.4).

   Before a Store is permitted, the storing peer MUST check that:

   o  The AOR of the request is a valid Resource Name with respect to
      the namespaces defined in the overlay configuration document.

   o  The certificate contains a username that is a SIP AOR which hashes
      to the Resource-ID it is being stored at.

   o  The certificate contains a Node-ID that is the same as the
      dictionary key it is being stored at.

   If any of these checks fail, the request MUST be rejected with an
   Error_Forbidden error.

   Note that these rules permit Alice to forward calls to Bob without
   his permission.  However, they do not permit Alice to forward Bob's
   calls to her.  See Section 8.2.2 for additional descriptions.

3.4.  Overlay Configuration Document Extension

   The use of a SIP-enabled overlay MAY be restricted to users with AORs
   from specific domains.  When deploying an overlay service, providers
   can decide about these use case scenarios by defining a set of
   namespaces for admissible domain names.  This section extends the
   overlay configuration document by defining new elements for patterns
   that describe a corresponding domain name syntax.

   A RELOAD overlay can be configured to accept store requests for any
   AOR, or to apply domain name restrictions.  To apply restrictions,
   the overlay configuration document needs to contain a <domain-
   restrictions> element.  The <domain-restrictions> element serves as a
   container for zero to multiple <pattern> sub-elements.  A <pattern>
   element MAY be present if the "enable" attribute of its parent
   element is set to true.  Each <pattern> element defines a pattern for
   constructing admissible resource names.  It is of type xsd:string and
   interpreted as a regular expression according to "POSIX Extended
   Regular Expression" (see the specifications in [IEEE-Posix]).



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   Encoding of the domain name complies to the restricted ASCII
   character set without character escaping as defined in Section 19.1
   of [RFC3261].

   Inclusion of a <domain-restrictions> element in an overlay
   configuration document is OPTIONAL.  If the element is not included,
   the default behavior is to accept any AOR.  If the element is
   included and the "enable" attribute is not set or set to false, the
   overlay MUST only accept AORs that match the domain name of the
   overlay.  If the element is included and the "enable" attribute is
   set to true, the overlay MUST only accept AORs that match patterns
   specified in the <domain-restrictions> element.

   Example of Domain Patterns:
   dht\.example\.com
   .*\.my\.example

   In this example, any AOR will be accepted that is either of the form
   <user>@dht.example.com, or ends with the domain "my.example".

   The Relax NG Grammar for the AOR Domain Restriction reads:

   # AOR DOMAIN RESTRICTION URN SUB-NAMESPACE

   namespace sip = "urn:ietf:params:xml:ns:p2p:config-base:sip"

   # AOR DOMAIN RESTRICTION ELEMENT

   Kind-parameter &= element sip:domain-restriction {

       attribute enable { xsd:boolean }

       # PATTERN ELEMENT

       element sip:pattern { xsd:string }*
   }?

4.  Looking up an AOR

4.1.  Finding a Route to an AOR

   A RELOAD user, member of an overlay, who wishes to call another user
   with given AOR SHALL proceed in the following way.

   AOR is GRUU?  If the AOR is a GRUU for this overlay, the callee can
      be contacted directly as described in Section 6.





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   AOR domain is hosted in overlay?  If the domain part of the AOR
      matches a domain pattern configured in the overlay, the user can
      continue to resolve the AOR in this overlay.  The user MAY choose
      to query the DNS service records to search for additional support
      of this domain name.

   AOR domain not supported by overlay?  If the domain part of the AOR
      is not supported in the current overlay, the user might query the
      DNS (or other discovery services at hand) to search for an
      alternative overlay that services the AOR under request.
      Alternatively, standard SIP procedures for contacting the callee
      might be used.

   AOR inaccessible?  If all of the above contact attempts fail, the
      call fails.

   The procedures described above likewise apply when nodes are
   simultaneously connected to several overlays.

4.2.  Resolving an AOR

   A RELOAD user that has discovered a route to an AOR in the current
   overlay SHALL execute the following steps.

   1.  Perform a Fetch for Kind SIP-REGISTRATION at the Resource-ID
       corresponding to the AOR.  This Fetch SHOULD NOT indicate any
       dictionary keys, so that it will fetch all the stored values.

   2.  If any of the results of the Fetch are non-GRUU AORs, then repeat
       step 1 for that AOR.

   3.  Once only GRUUs and destination lists remain, the peer removes
       duplicate destination lists and GRUUs from the list and initiates
       SIP or SIPS connections to the appropriate peers as described in
       the following sections.  If there are also external AORs, the
       peer follows the appropriate procedure for contacting them as
       well.

5.  Forming a Direct Connection

5.1.  Setting Up a Connection

   Once the peer has translated the AOR into a set of destination lists,
   it then uses the overlay to route AppAttach messages to each of those
   peers.  The "application" field MUST be either 5060 to indicate SIP
   or 5061 for using SIPS.  If certificate-based authentication is in
   use, the responding peer MUST present a certificate with a Node-ID
   matching the terminal entry in the destination list.  Otherwise, the



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   connection MUST NOT be used and MUST be closed.  Note that it is
   possible that the peers already have a RELOAD connection mutually
   established.  This MUST NOT be used for SIP messages unless it is a
   SIP connection.  A previously established SIP connection MAY be used
   for a new call.

   Once the AppAttach succeeds, the peer sends plain or (D)TLS encrypted
   SIP messages over the connection as in normal SIP.  A caller MAY
   choose to contact the callee using SIP or SIPS, but SHOULD follow a
   preference indicated by the callee in its contact_prefs attribute
   (see Section 3.2).  A callee MAY choose to listen on both SIP and
   SIPS ports and accept calls from either SIP scheme, or select a
   single one.  However, a callee that decides to accept SIPS calls,
   only, SHOULD indicate its choice by setting the corresponding
   attribute in its contact_prefs.  It is noteworthy that according to
   [RFC6940] all overlay links are built on (D)TLS secured transport.
   While hop-wise encrypted paths do not prevent the use of plain SIP,
   SIPS requires protection of all links that may include client links
   (if present) and endpoint certificates.

   SIP messages carry the SIP URIs of actual overlay endpoints (e.g.,
   "sip:alice@dht.example.com") in the Via and Contact headers, while
   the communication continues via the RELOAD connection.  However, a UA
   can redirect its communication path by setting an alternate Contact
   header field like in ordinary SIP.

5.2.  Keeping a Connection Alive

   In many cases, RELOAD connections will traverse NATs and Firewalls
   that maintain states established from ICE [RFC5245] negotiations.  It
   is the responsibility of the Peers to provide sufficiently frequent
   traffic to keep NAT and Firewall states present and the connection
   alive.  Keepalives are a mandatory component of ICE (see Section 10
   of [RFC5245]) and no further operations are required.  Applications
   that want to assure maintenance of sessions individually need to
   follow regular SIP means.  Accordingly, a SIP Peer MAY apply keep-
   alive techniques in agreement with its transport binding as defined
   in Section 3.5 of [RFC5626].

6.  Using GRUUs

   Globally Routable User Agent URIs (GRUUs) [RFC5627] have been
   designed to allow direct routing to a specific UA instance without
   the need for dereferencing by a domain-specific SIP proxy function.
   The concept is transferred to RELOAD overlays as follows.  GRUUs in
   RELOAD are constructed by embedding a base64-encoded destination list
   in the "gr" URI parameter of the GRUU.  The base64 encoding is done




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   with the alphabet specified in table 1 of [RFC4648] with the
   exception that ~ is used in place of =.

   Example of a RELOAD GRUU:
   alice@example.com;gr=MDEyMzQ1Njc4OTAxMjM0NTY3ODk~

   GRUUs do not require to store data in the Overlay Instance.  Rather
   when a peer needs to route a message to a GRUU in the same P2P
   overlay, it simply uses the destination list and connects to that
   peer.  Because a GRUU contains a destination list, it can have the
   same contents as a destination list stored elsewhere in the resource
   dictionary.

   Anonymous GRUUs [RFC5767] are constructed analogously, but require
   either that the enrollment server issues a different Node-ID for each
   anonymous GRUU required, or that a destination list be used that
   includes a peer that compresses the destination list to stop the
   Node-ID from being revealed.

7.  SIP-REGISTRATION Kind Definition

   This section defines the SIP-REGISTRATION Kind.



   Name  SIP-REGISTRATION



   Kind IDs  The Resource Name for the SIP-REGISTRATION Kind-ID is the
      AOR of the user as specified in Section 2.  The data stored is a
      SipRegistration, which can contain either another URI or a
      destination list to the peer which is acting for the user.



   Data Model  The data model for the SIP-REGISTRATION Kind-ID is
      dictionary.  The dictionary key is the Node-ID of the storing
      peer.  This allows each peer (presumably corresponding to a single
      device) to store a single route mapping.



   Access Control  USER-NODE-MATCH.  Note that this matches the SIP AOR
      against the rfc822Name in the X509v3 certificate.  The rfc822Name
      does not include the scheme so that the "sip:" prefix needs to be
      removed from the SIP AOR before matching.  Escaped characters ('%'




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      encoding) in the SIP AOR also need to be decoded prior to matching
      (see [RFC3986]).

   Data stored under the SIP-REGISTRATION Kind is of type
   SipRegistration.  This comes in two varieties:



   sip_registration_uri

      a URI which the user can be reached at.



   sip_registration_route

      a destination list which can be used to reach the user's peer.

8.  Security Considerations

8.1.  RELOAD-Specific Issues

   This Usage for RELOAD does not define new protocol elements or
   operations.  Hence no new threats arrive from message exchanges in
   RELOAD.

   This document introduces an AOR domain restriction function that must
   be surveyed by the storing peer.  A misconfigured or malicious peer
   could cause frequent rejects of illegitimate storing requests.
   However, domain name control relies on a lightweight pattern matching
   and can be processed prior to validating certificates.  Hence no
   extra burden is introduced for RELOAD peers beyond loads already
   present in the base protocol.

8.2.  SIP-Specific Issues

8.2.1.  Fork Explosion

   Because SIP includes a forking capability (the ability to retarget to
   multiple recipients), fork bombs (i.e., attacks using SIP forking to
   amplify the effect on the intended victims) are a potential DoS
   concern.  However, in the SIP usage of RELOAD, fork bombs are a much
   lower concern than in a conventional SIP Proxy infrastructure,
   because the calling party is involved in each retargeting event.  It
   can therefore directly measure the number of forks and throttle at
   some reasonable number.





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8.2.2.  Malicious Retargeting

   Another potential DoS attack is for the owner of an attractive AOR to
   retarget all calls to some victim.  This attack is common to SIP and
   difficult to ameliorate without requiring the target of a SIP
   registration to authorize all stores.  The overhead of that
   requirement would be excessive and in addition there are good use
   cases for retargeting to a peer without its explicit cooperation.

8.2.3.  Misuse of AORs

   A RELOAD overlay and enrollment service that liberally accept
   registrations for AORs of domain names unrelated to the overlay
   instance and without further authorisation, eventually store presence
   state for misused AORs.  An attacker could hijack names, register a
   bogus presence and attract calls dedicated to a victim that resides
   within or outside the Overlay Instance.

   A hijacking of AORs can be mitigated by restricting the name spaces
   admissible in the Overlay Instance, or by additional verification
   actions of the enrollment service.  To prevent an (exclusive) routing
   to a bogus registration, a caller can in addition query the DNS (or
   other discovery services at hand) to search for an alternative
   presence of the callee in another overlay or a normal SIP
   infrastructure.

8.2.4.  Privacy Issues

   All RELOAD SIP registration data is visible to all nodes in the
   overlay.  Location privacy can be gained from using anonymous GRUUs.
   Methods of providing anonymity or deploying pseudonyms exist, but are
   beyond the scope of this document.

9.  IANA Considerations

9.1.  Data Kind-ID

   IANA shall register the following code point in the "RELOAD Data
   Kind-ID" Registry (cf., [RFC6940]) to represent the SIP-REGISTRATION
   Kind, as described in Section 7.  [NOTE TO IANA/RFC-EDITOR: Please
   replace RFC-AAAA with the RFC number for this specification in the
   following list.]

              +---------------------+------------+----------+
              | Kind                |    Kind-ID |      RFC |
              +---------------------+------------+----------+
              | SIP-REGISTRATION    |          1 | RFC-AAAA |
              +---------------------+------------+----------+



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9.2.  XML Name Space Registration

   This document registers the following URI for the config XML
   namespace in the IETF XML registry defined in [RFC3688]

   URI:  urn:ietf:params:xml:ns:p2p:config-base:sip

   Registrant Contact:  The IESG

   XML:  N/A, the requested URI is an XML namespace

10.  Acknowledgments

   This document was generated in parts from initial drafts and
   discussions in the early specification phase of the P2PSIP base
   protocol.  Significant contributions (in alphabetical order) were
   from David A.  Bryan, James Deverick, Marcin Matuszewski, Jonathan
   Rosenberg, and Marcia Zangrilli, which is gratefully acknowledged.

   Additional thanks go to all those who helped with ideas, discussions,
   and reviews, in particular (in alphabetical order) Roland Bless,
   Michael Chen, Alissa Cooper, Marc Petit-Huguenin, Brian Rosen, Meral
   Shirazipour, and Matthias Waehlisch.

11.  References

11.1.  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>.

   [RFC6940]  Jennings, C., Lowekamp, B., Ed., Rescorla, E., Baset, S.,
              and H. Schulzrinne, "REsource LOcation And Discovery
              (RELOAD) Base Protocol", RFC 6940, DOI 10.17487/RFC6940,
              January 2014, <http://www.rfc-editor.org/info/rfc6940>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <http://www.rfc-editor.org/info/rfc3261>.

   [RFC2533]  Klyne, G., "A Syntax for Describing Media Feature Sets",
              RFC 2533, DOI 10.17487/RFC2533, March 1999,
              <http://www.rfc-editor.org/info/rfc2533>.




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   [RFC2738]  Klyne, G., "Corrections to "A Syntax for Describing Media
              Feature Sets"", RFC 2738, DOI 10.17487/RFC2738, December
              1999, <http://www.rfc-editor.org/info/rfc2738>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <http://www.rfc-editor.org/info/rfc3688>.

   [RFC3840]  Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
              "Indicating User Agent Capabilities in the Session
              Initiation Protocol (SIP)", RFC 3840,
              DOI 10.17487/RFC3840, August 2004,
              <http://www.rfc-editor.org/info/rfc3840>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <http://www.rfc-editor.org/info/rfc4648>.

   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245,
              DOI 10.17487/RFC5245, April 2010,
              <http://www.rfc-editor.org/info/rfc5245>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <http://www.rfc-editor.org/info/rfc5280>.

   [RFC5626]  Jennings, C., Ed., Mahy, R., Ed., and F. Audet, Ed.,
              "Managing Client-Initiated Connections in the Session
              Initiation Protocol (SIP)", RFC 5626,
              DOI 10.17487/RFC5626, October 2009,
              <http://www.rfc-editor.org/info/rfc5626>.

   [RFC5627]  Rosenberg, J., "Obtaining and Using Globally Routable User
              Agent URIs (GRUUs) in the Session Initiation Protocol
              (SIP)", RFC 5627, DOI 10.17487/RFC5627, October 2009,
              <http://www.rfc-editor.org/info/rfc5627>.






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   [IEEE-Posix]
              "IEEE Standard for Information Technology - Portable
              Operating System Interface (POSIX) - Part 2: Shell and
              Utilities (Vol.  1)", IEEE Std 1003.2-1992, ISBN
              1-55937-255-9, January 1993.

11.2.  Informative References

   [I-D.ietf-p2psip-concepts]
              Bryan, D., Matthews, P., Shim, E., Willis, D., and S.
              Dawkins, "Concepts and Terminology for Peer to Peer SIP",
              draft-ietf-p2psip-concepts-09 (work in progress), April
              2016.

   [RFC5767]  Munakata, M., Schubert, S., and T. Ohba, "User-Agent-
              Driven Privacy Mechanism for SIP", RFC 5767,
              DOI 10.17487/RFC5767, April 2010,
              <http://www.rfc-editor.org/info/rfc5767>.

   [I-D.ietf-p2psip-share]
              Knauf, A., Schmidt, T., Hege, G., and M. Waehlisch, "A
              Usage for Shared Resources in RELOAD (ShaRe)", draft-ietf-
              p2psip-share-08 (work in progress), March 2016.

Appendix A.  Third Party Registration

   In traditional SIP, the mechanism of a third party registration
   (i.e., an assistant acting for a boss, changing users register a
   role-based AOR, ...) is defined in Section 10.2 of [RFC3261].  This
   is a REGISTER which uses the URI of the third-party in its From
   header and cannot be translated directly into a P2PSIP registration,
   because only the owner of the certificate can store a SIP-
   REGISTRATION in a RELOAD overlay.

   A way to implement third party registration is by using the extended
   access control mechanism USER-CHAIN-ACL defined in
   [I-D.ietf-p2psip-share].  Creating a new Kind "SIP-3P-REGISTRATION"
   that is ruled by USER-CHAIN-ACL allows the owner of the certificate
   to delegate the right for registration to individual third parties.
   In this way, original SIP functionality can be regained without
   weakening the security control of RELOAD.

Appendix B.  Change Log








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B.1.  Changes since draft-ietf-p2psip-sip-09

   o  Added subsection on keepalive

   o  Updated references

B.2.  Changes since draft-ietf-p2psip-sip-08

   o  Added the handling of SIPS

   o  Specified use of Posix regular expressions in configuration
      document

   o  Added IANA registration for namespace

   o  Editorial polishing

   o  Updated and extended references

B.3.  Changes since draft-ietf-p2psip-sip-07

   o  Cleared open issues

   o  Clarified use cases after WG discussion

   o  Added configuration document extensions for configurable domain
      names

   o  Specified format of contact_prefs

   o  Clarified routing to AORs

   o  Extended security section

   o  Added Appendix on Third Party Registration

   o  Added IANA code points

   o  Editorial polishing

   o  Updated and extended references

B.4.  Changes since draft-ietf-p2psip-sip-06

   o  Added Open Issue






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Authors' Addresses

   Cullen Jennings
   Cisco
   170 West Tasman Drive
   MS: SJC-21/2
   San Jose, CA  95134
   USA

   Phone: +1 408 421-9990
   Email: fluffy@cisco.com


   Bruce B. Lowekamp
   Skype
   Palo Alto, CA
   USA

   Email: bbl@lowekamp.net


   Eric Rescorla
   RTFM, Inc.
   2064 Edgewood Drive
   Palo Alto, CA  94303
   USA

   Phone: +1 650 678 2350
   Email: ekr@rtfm.com


   Salman A. Baset
   Columbia University
   1214 Amsterdam Avenue
   New York, NY
   USA

   Email: salman@cs.columbia.edu


   Henning Schulzrinne
   Columbia University
   1214 Amsterdam Avenue
   New York, NY
   USA

   Email: hgs@cs.columbia.edu




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   Thomas C. Schmidt (editor)
   HAW Hamburg
   Berliner Tor 7
   Hamburg  20099
   Germany

   Email: t.schmidt@haw-hamburg.de












































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