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RFC 7843

Proposed STD
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Port Control Protocol (PCP) Third-Party ID Option

Updates:    6887


Top       ToC       Page 1 
Internet Engineering Task Force (IETF)                          A. Ripke
Request for Comments: 7843                                     R. Winter
Updates: 6887                                                   T. Dietz
Category: Standards Track                                     J. Quittek
ISSN: 2070-1721                                                      NEC
                                                             R. da Silva
                                                          Telefonica I+D
                                                                May 2016


           Port Control Protocol (PCP) Third-Party ID Option

Abstract

   This document describes a new Port Control Protocol (PCP) option
   called the THIRD_PARTY_ID option.  It is designed to be used together
   with the THIRD_PARTY option specified in RFC 6887.

   The THIRD_PARTY_ID option serves to identify a third party in
   situations where a third party's IP address contained in the
   THIRD_PARTY option does not provide sufficient information to create
   requested mappings in a PCP-controlled device.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7843.

Page 2 
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
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Target Scenarios  . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Carrier-Hosted UPnP IGD-PCP IWF . . . . . . . . . . . . .   6
     3.2.  Carrier Web Portal  . . . . . . . . . . . . . . . . . . .   7
   4.  Format  . . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     4.1.  Result Codes  . . . . . . . . . . . . . . . . . . . . . .  10
   5.  Behavior  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
     5.1.  Generating a Request  . . . . . . . . . . . . . . . . . .  10
     5.2.  Processing a Request  . . . . . . . . . . . . . . . . . .  11
     5.3.  Processing a Response . . . . . . . . . . . . . . . . . .  11
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

Top      ToC       Page 3 
1.  Introduction

   The IETF has specified the Port Control Protocol (PCP) [RFC6887] to
   control how packets are translated and/or forwarded by a PCP-
   controlled device such as a Network Address Translator (NAT) or a
   firewall.

   This document focuses on scenarios where the PCP client sends
   requests that concern internal addresses other than the address of
   the PCP client itself.

   There is already an option defined for this purpose in [RFC6887]
   called the THIRD_PARTY option.  The THIRD_PARTY option carries the IP
   address of a host for which a PCP client requests an action at the
   PCP server.  For example, the THIRD_PARTY option can be used if port
   mapping requests for a Carrier-Grade NAT (CGN) are not sent from PCP
   clients at subscriber terminals but instead from a PCP Interworking
   Function (IWF), which requests port mappings.

   In some cases, the THIRD_PARTY option alone is not sufficient and
   further means are needed for identifying the third party.  Such cases
   are addressed by the THIRD_PARTY_ID option, which is specified in
   this document.

   The primary issue addressed by the THIRD_PARTY_ID option is that
   there are CGN deployments that do not distinguish internal hosts by
   their IP address alone, but use further identifiers (IDs) for unique
   subscriber identification.  For example, this is the case if a CGN
   supports overlapping private or shared IP address spaces [RFC1918]
   [RFC6598] for internal hosts of different subscribers.  In such
   cases, different internal hosts are identified and mapped at the CGN
   by their IP address and/or another ID, for example, the ID of a
   tunnel between the CGN and the subscriber.  In these scenarios (and
   similar ones), the internal IP address contained in the THIRD_PARTY
   option is not sufficient to demultiplex connections from internal
   hosts.  An additional identifier needs to be present in the PCP
   message in order to uniquely identify an internal host.  The
   THIRD_PARTY_ID option is used to carry this ID.

   This applies to some of the PCP deployment scenarios that are listed
   in Section 2.1 of [RFC6887], in particular to a L2-aware NAT, which
   is described in more detail in Section 3, as well as in other
   scenarios where overlapping address spaces occur like in [RFC6674] or
   [RFC6619].

   The THIRD_PARTY_ID option is defined for the PCP opcodes MAP and PEER
   to be used together with the THIRD_PARTY option, which is specified
   in [RFC6887].

Top      ToC       Page 4 
2.  Terminology

   The terminology defined in the specification of PCP [RFC6887]
   applies.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in RFC
   2119 [RFC2119].

3.  Target Scenarios

   This section describes two scenarios that illustrate the use of the
   THIRD_PARTY_ID option:

   1.  A UPnP IGD-PCP IWF (Universal Plug and Play Internet Gateway
       Device - Port Control Protocol Interworking Function [RFC6970]).

   2.  A carrier web portal for port mapping.

   These are just two examples that illustrate the use and applicability
   of the THIRD_PARTY_ID option.  While these are just two examples,
   there might be other conceivable use cases.  However, the use of the
   THIRD_PARTY_ID option as specified in this document is restricted to
   scenarios where the option is needed for the purpose of uniquely
   identifying an internal host in addition to the information found in
   the THIRD_PARTY option.

   Both scenarios elaborated in this document are refinements of the
   same basic scenario shown in Figure 1 that is considered as a PCP
   deployment scenario employing L2-aware NATs as listed in Section 2.1
   of [RFC6887].  It has a carrier operating a CGN and a Port Control
   Protocol Interworking Function (PCP IWF) [RFC6970] for subscribers to
   request port mappings at the CGN.  The PCP IWF communicates with the
   CGN using PCP.  For this purpose, the PCP IWF contains a PCP client
   serving multiple subscribers and the CGN is co-located with a PCP
   server.  The way subscribers interact with the PCP IWF for requesting
   port mappings for their internal hosts is not specified in this basic
   scenario, but it is elaborated on more in the specific scenarios in
   Sections 3.1 and 3.2.

   The CGN operates as a L2-aware NAT.  Unlike a standard NAT, it
   includes a subscriber identifier in addition to the source IP address
   in entries of the NAT mapping table.

Top      ToC       Page 5 
   +--------------+    +------------------+
   | Subscriber   |    | Carrier          |    ==== L2 connection(s)
   |              |    | +--------------+ |         between subscriber
   |              +......+ PCP          | |         and CGN
   | +----------+ |    | | Interworking | |    #### PCP communication
   | | Internal | |    | | Function     | |    .... Subscriber-IWF
   | | Host     | |    | +-----#--------+ |         interaction
   | +----+-----+ |    |       #          |         (elaborated
   |      |       |    | +-----#--------+ |         in specific
   | +----+-----+ |    | | PCP Server   | |         scenarios below)
   | |  CPE     | |    | |              | |
   | |          +-+======+ CGN L2NAT    +--------- Public Internet
   | +----------+ |    | +--------------+ |
   +--------------+    +------------------+

        Figure 1: Carrier Hosted PCP IWF for Port Mapping Requests

   Internal hosts in the subscriber's network use private IP addresses
   [RFC1918].  There is no NAT between the internal host and the CGN,
   and there is an overlap of addresses used by internal hosts of
   different subscribers.  That is why the CGN needs more than just the
   internal host's IP address to distinguish internal hosts of different
   subscribers.  A commonly deployed method for solving this issue is
   using an additional identifier for this purpose.  A natural candidate
   for this additional identifier at the CGN is the ID of the tunnel
   that connects the CGN to the subscriber's network.  The subscriber's
   Customer Premises Equipment (CPE) operates as a Layer 2 bridge.

   Requests for port mappings from the PCP IWF to the CGN need to
   uniquely identify the internal host for which a port mapping is to be
   established or modified.  Already existing for this purpose is the
   THIRD_PARTY option that can be used to specify the internal host's IP
   address.  The THIRD_PARTY_ID option is introduced for carrying the
   additional third-party information needed to identify the internal
   host in this scenario.

   The additional identifier for internal hosts needs to be included in
   MAP requests from the PCP IWF in order to uniquely identify the
   internal host that should have its address mapped.  This is the
   purpose that the new THIRD_PARTY_ID option serves in this scenario.
   It carries the additional identifier, that is the tunnel ID, that
   serves for identifying an internal host in combination with the
   internal host's (private) IP address.  The IP address of the internal
   host is included in the PCP IWF's mapping requests by using the
   THIRD_PARTY option.

Top      ToC       Page 6 
   The information carried by the THIRD_PARTY_ID option is not just
   needed to identify an internal host in a PCP request.  The CGN needs
   this information in its internal mapping tables for translating
   packet addresses and for forwarding packets to subscriber-specific
   tunnels.

   How the carrier PCP IWF is managing port mappings, such as, for
   example, automatically extending the lifetime of a mapping, is beyond
   the scope of this document.

3.1.  Carrier-Hosted UPnP IGD-PCP IWF

   This scenario further elaborates the basic one above by choosing
   UPnP-IGD as the communication protocol between the subscriber and the
   carrier's PCP IWF.  Then obviously, the PCP IWF is realized as a UPnP
   IGD-PCP IWF as specified in [RFC6970].

   As shown in Figure 2, it is assumed here that the UPnP IGD-PCP IWF is
   not embedded in the subscriber premises router, but offered as a
   service to the subscriber.  Further, it is assumed that the UPnP IGD-
   PCP IWF is not providing NAT functionality.

   This requires that the subscriber can connect to the UPnP IGD-PCP IWF
   to request port mappings at the CGN using UPnP-IGD as specified in
   [RFC6970].  In this scenario, the connection is provided via (one of
   the) tunnel(s) connecting the subscriber's network to the Broadband
   Remote Access Server (BRAS) and an extension of this tunnel from the
   BRAS to the UPnP IGD-PCP IWF.  Note that there are other alternatives
   that can be used for providing the connection to the UPnP IGD-PCP
   IWF.  The tunnel extension used in this scenario can, for example, be
   realized by a forwarding function for UPnP messages at the BRAS that
   forwards such messages through per-subscriber tunnels to the UPnP
   IGD-PCP IWF.  Depending on an actual implementation, the UPnP IGD-PCP
   IWF can then either use the ID of the tunnel in which the UPnP
   message arrived directly as the THIRD_PARTY_ID option for PCP
   requests to the CGN, or it uses the ID of the tunnel to retrieve the
   THIRD_PARTY_ID option from the Authentication, Authorization, and
   Accounting (AAA) server.

   To support the latter option, the BRAS needs to register the
   subscriber's tunnel IDs at the AAA server at the time it contacts the
   AAA server for authentication and/or authorization of the subscriber.
   The tunnel IDs to be registered per subscriber at the AAA server may
   include the tunnel between CPE and BRAS, between BRAS and UPnP IGD-
   PCP IWF, and between BRAS and CGN.  The UPnP IGD-PCP IWF queries the
   AAA server for the ID of the tunnel between BRAS and CGN, because
   this is the identifier to be used as the THIRD_PARTY_ID option in the
   subsequent port mapping request.

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   +--------------+    +------------------------------------+
   | Subscriber   |    | Carrier                            |
   |              |    | +----------------------------+     |
   |              |    | |          AAA Server        |     |
   |              |    | +-----+---------------+------+     |
   |              |    |       |               |            |
   | +----------+ |    | +-----+---+     +-----+------+     |
   | | Internal | |    | |         +=====+            |     |
   | | Host     | |    | |    ...........| UPnP IGD   |     |
   | +----+-----+ |    | |    .    +=====+ PCP IWF    |     |
   |      |  .    |    | |    .    |     +-----#------+     |
   | +----+--.--| |    | |    .    |           #            |
   | |    |  .  +========+    .    |     +-----#------+     |
   | |    |  ..................    +=====+ PCP Server |     |
   | |    +------------------------------|            |     |
   | |  CPE     +========+  BRAS   +=====+ CGN L2NAT  +------- Public
   | +----------+ |    | +---------+     +------------+     |  Internet
   +--------------+    +------------------------------------+

   ==== L2 tunnel borders between subscriber, BRAS, IWF, and CGN
   .... UPnP communication
   #### PCP communication

                        Figure 2: UPnP IGD-PCP IWF

   A potential extension to [RFC6970] regarding an additional state
   variable for the THIRD_PARTY_ID option and regarding an additional
   error code for a mismatched THIRD_PARTY_ID option and its processing
   might be a logical next step.  However, this is not in the scope of
   this document.

3.2.  Carrier Web Portal

   This scenario shown in Figure 3 is different from the previous one
   concerning the protocol used between the subscriber and the IWF.
   Here, HTTP(S) is the protocol that the subscriber uses for port
   mapping requests.  The subscriber may make requests manually using a
   web browser or automatically -- as in the previous scenario -- with
   applications in the subscriber's network issuing port mapping
   requests on demand.  The web portal queries the AAA server for the
   subscriber's ID of the tunnel (BRAS to CGN) that was reported by the
   BRAS.  The returned ID of the tunnel (BRAS to CGN) is used as the
   THIRD_PARTY_ID option in the subsequent port mapping request.

Top      ToC       Page 8 
   +--------------+    +------------------------------------+
   | Subscriber   |    | Carrier                            |
   |              |    |                 +------------+     |
   |              |    | +------------+  | Web Portal |     |
   | +----------+ |    | | AAA Server +--+            +--+  |
   | | Internal | |    | +-----+------+  | PCP Client |  |  |
   | | Host     | |    |       |         +-----#------+  |  |
   | +----+-----+ |    |       |               #         |  |
   |      |       |    | +-----+---+     +-----#------+  |  |
   | +----+-----+ |    | |         |     | PCP Server |  |  |
   | |  CPE     | |    | |  BRAS   |     |            |  |  |
   | |          +-+======+         +=====+ CGN L2NAT  +--+---- Public
   | +----------+ |    | +---------+     +------------+     |  Internet
   +--------------+    +------------------------------------+

   ==== L2 tunnel(s) between subscriber, BRAS, and CGN
   #### PCP communication

                       Figure 3: Carrier Web Portal

   The PCP IWF is realized as a combination of a web server and a PCP
   client.

Top      ToC       Page 9 
4.  Format

   The THIRD_PARTY_ID option as shown in Figure 4 uses the format of PCP
   options as specified in [RFC6887]:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Option Code=13 |  Reserved     |      Option Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                      THIRD_PARTY_ID                           |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Option Name:         THIRD_PARTY_ID
   Option Code:         13
   Purpose:             Together with the THIRD_PARTY option, the
                        THIRD_PARTY_ID option identifies a third party
                        for which a request for an external IP address
                        and port is made.
   Valid for Opcodes:   MAP, PEER
   Length:              Variable; maximum 1016 octets.
   May appear in:       Request. May appear in response only if it
                        appeared in the associated request.
   Maximum occurrences: 1

                      Figure 4: THIRD_PARTY_ID Option

   The "Reserved" field and the "Option length" field are to be set as
   specified in Section 7.3 of [RFC6887].

   The "THIRD_PARTY_ID" field contains a deployment-specific identifier
   that identifies a realm of a NAT map entry.  Together with a
   THIRD_PARTY option it can be used to identify a subscriber's session
   on a PCP-controlled device.  It has no other semantics.

   The "THIRD_PARTY_ID" is not bound to any specific identifier.  It can
   contain any deployment-specific value that the PCP client and the PCP
   server agree on.  How this agreement is reached if both PCP server
   and client are not administered by the same entity is beyond the
   scope of this document.  Also, the client does not need to have an
   understanding of how the ID is being used at the PCP server.

   If an identifier is used that is based on an existing standard, then
   the encoding rules of that standard must be followed.  As an example,
   in case a session ID of the Layer 2 Tunneling Protocol version 3

Top      ToC       Page 10 
   (L2TPv3) [RFC3931] is being used, then that identifier has to be
   encoded the same way it would be encoded in the L2TPv3 session
   header.  This allows for a simple octet-by-octet comparison at the
   PCP-controlled device.

   [RFC6887] expects option data to always come in multiples of an
   octet.  An ID, however, might not fulfill this criterion.  As an
   example, an MPLS label is 20 bits wide.  In these cases, padding is
   done by appending 0 bits until the byte boundary is reached.  After
   that, the padding rules of [RFC6887] apply.

   The option number is in the mandatory-to-process range (0-127),
   meaning that a request with a THIRD_PARTY_ID option is processed by
   the PCP server if and only if the THIRD_PARTY_ID option is supported
   by the PCP server.  Therefore, it should not be included unless the
   PCP client is certain that a mapping without the THIRD_PARTY_ID is
   impossible.

4.1.  Result Codes

   The following PCP Result Codes are new:

   24:  THIRD_PARTY_ID_UNKNOWN: The provided identifier in a
        THIRD_PARTY_ID option is unknown/unavailable to the PCP server.
        This is a long lifetime error.

   25:  THIRD_PARTY_MISSING_OPTION: This error occurs if both
        THIRD_PARTY and THIRD_PARTY_ID options are expected in a request
        but one option is missing.  This is a long lifetime error.

   26:  UNSUPP_THIRD_PARTY_ID_LENGTH: The received option length is not
        supported.  This is a long lifetime error.

5.  Behavior

   The following sections describe the operations of a PCP client and a
   PCP server when generating the request and processing the request and
   response.

5.1.  Generating a Request

   In addition to generating a PCP request that is described in
   [RFC6887], the following has to be applied.  The THIRD_PARTY_ID
   option MAY be included either in a PCP MAP or PEER opcode.  It MUST
   be used in combination with the THIRD_PARTY option, which provides an
   IP address.  The THIRD_PARTY_ID option holds an identifier to allow
   the PCP-controlled device to uniquely identify the internal host

Top      ToC       Page 11 
   (specified in the THIRD_PARTY option) for which the port mapping is
   to be established or modified.  The padding rules described in
   Section 4 apply.

5.2.  Processing a Request

   The THIRD_PARTY_ID option is in the mandatory-to-process range; if
   the PCP server does not support this option, it MUST return an
   UNSUPP_OPTION response.  If the provided identifier in a
   THIRD_PARTY_ID option is unknown/unavailable, the PCP server MUST
   return a THIRD_PARTY_ID_UNKNOWN response.  If the PCP server receives
   a request with an unsupported THIRD_PARTY_ID option length, it MUST
   return an UNSUPP_THIRD_PARTY_ID_LENGTH response.  If the PCP server
   receives a THIRD_PARTY_ID option without a THIRD_PARTY option, it
   MUST return a THIRD_PARTY_MISSING_OPTION response.

   Upon receiving a valid request with a legal THIRD_PARTY_ID option
   identifier, the message is processed as specified in [RFC6887],
   except that the identifier contained in the THIRD_PARTY_ID is used in
   addition when accessing a mapping table.  Instead of just using the
   value contained in the THIRD_PARTY option when accessing the internal
   Internet address of a mapping table, now the combination of the two
   values contained in the THIRD_PARTY option and in the THIRD_PARTY_ID
   option is used to access the combination of the internal Internet
   address and the internal realm of a NAT map entry.

   If two or more different tunnel technologies are being used,
   precautions need to be taken to handle potential overlap of the ID
   spaces of these technologies.  For example, different PCP client/PCP
   server pairs can be used per tunnel technology.

5.3.  Processing a Response

   In addition to the response processing described in [RFC6887], if the
   PCP client receives a THIRD_PARTY_ID_UNKNOWN or a
   UNSUPP_THIRD_PARTY_ID_LENGTH or a THIRD_PARTY_MISSING_OPTION response
   back for its previous request, it SHOULD report an error.  Where to
   report an error is based on policy.

6.  IANA Considerations

   The following PCP Option Code has been allocated in the mandatory-to-
   process range:

   o  13: THIRD_PARTY_ID

Top      ToC       Page 12 
   The following PCP Result Codes have been allocated:

   o  24: THIRD_PARTY_ID_UNKNOWN

   o  25: THIRD_PARTY_MISSING_OPTION

   o  26: UNSUPP_THIRD_PARTY_ID_LENGTH

7.  Security Considerations

   This option is to be used in combination with the THIRD_PARTY option.
   Consequently, all corresponding security considerations in
   Section 18.1.1 of [RFC6887] apply.  In particular, the network on
   which the PCP messages are sent must be sufficiently protected.
   Further, it is RECOMMENDED to use PCP authentication [RFC7652] unless
   the network already has appropriate authentication means in place.

   The THIRD_PARTY_ID option carries a context identifier whose type and
   length is deployment and implementation dependent.  This identifier
   might carry privacy sensitive information.  It is therefore
   RECOMMENDED to utilize identifiers that do not have such privacy
   concerns.  Means to protect unauthorized access to this information
   MUST be put in place.  In the scenarios described in this document,
   for example, access to the web portal or UPnP IGD-PCP IWF MUST be
   authenticated.  Generally speaking, the identifier itself MUST only
   be accessible by the network operator and MUST only be handled on
   operator equipment.  For example, creation of a PCP message on the
   web portal or the UPnP IGD PCP IWF is triggered by the subscriber,
   but the actual option filling is done by an operator-controlled
   entity.

8.  References

8.1.  Normative References

   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
              and E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,
              <http://www.rfc-editor.org/info/rfc1918>.

   [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>.

Top      ToC       Page 13 
   [RFC6598]  Weil, J., Kuarsingh, V., Donley, C., Liljenstolpe, C., and
              M. Azinger, "IANA-Reserved IPv4 Prefix for Shared Address
              Space", BCP 153, RFC 6598, DOI 10.17487/RFC6598, April
              2012, <http://www.rfc-editor.org/info/rfc6598>.

   [RFC6887]  Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
              P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
              DOI 10.17487/RFC6887, April 2013,
              <http://www.rfc-editor.org/info/rfc6887>.

8.2.  Informative References

   [RFC3931]  Lau, J., Ed., Townsley, M., Ed., and I. Goyret, Ed.,
              "Layer Two Tunneling Protocol - Version 3 (L2TPv3)",
              RFC 3931, DOI 10.17487/RFC3931, March 2005,
              <http://www.rfc-editor.org/info/rfc3931>.

   [RFC6619]  Arkko, J., Eggert, L., and M. Townsley, "Scalable
              Operation of Address Translators with Per-Interface
              Bindings", RFC 6619, DOI 10.17487/RFC6619, June 2012,
              <http://www.rfc-editor.org/info/rfc6619>.

   [RFC6674]  Brockners, F., Gundavelli, S., Speicher, S., and D. Ward,
              "Gateway-Initiated Dual-Stack Lite Deployment", RFC 6674,
              DOI 10.17487/RFC6674, July 2012,
              <http://www.rfc-editor.org/info/rfc6674>.

   [RFC6970]  Boucadair, M., Penno, R., and D. Wing, "Universal Plug and
              Play (UPnP) Internet Gateway Device - Port Control
              Protocol Interworking Function (IGD-PCP IWF)", RFC 6970,
              DOI 10.17487/RFC6970, July 2013,
              <http://www.rfc-editor.org/info/rfc6970>.

   [RFC7652]  Cullen, M., Hartman, S., Zhang, D., and T. Reddy, "Port
              Control Protocol (PCP) Authentication Mechanism",
              RFC 7652, DOI 10.17487/RFC7652, September 2015,
              <http://www.rfc-editor.org/info/rfc7652>.

Top      ToC       Page 14 
Acknowledgments

   Thanks to Mohamed Boucadair for many valuable suggestions, in
   particular for suggesting a variable length for the THIRD_PARTY_ID
   option.  Thanks to Dave Thaler, Tom Taylor, and Dan Wing for their
   comments and review.

Authors' Addresses

   Andreas Ripke
   NEC
   Heidelberg
   Germany

   Email: ripke@neclab.eu


   Rolf Winter
   NEC
   Heidelberg
   Germany

   Email: winter@neclab.eu


   Thomas Dietz
   NEC
   Heidelberg
   Germany

   Email: dietz@neclab.eu


   Juergen Quittek
   NEC
   Heidelberg
   Germany

   Email: quittek@neclab.eu


   Rafael Lopez da Silva
   Telefonica I+D
   Madrid
   Spain

   Email: rafaelalejandro.lopezdasilva@telefonica.com