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PROPOSED STANDARD
Internet Engineering Task Force (IETF)                            Q. SunRequest for Comments: 7753                                 China TelecomCategory: Standards Track                                   M. BoucadairISSN: 2070-1721                                           France Telecom                                                            S. Sivakumar                                                           Cisco Systems                                                                 C. Zhou                                                     Huawei Technologies                                                                 T. Tsou                                                        Philips Lighting                                                            S. Perreault                                                     Jive Communications                                                           February 2016Port Control Protocol (PCP) Extension for Port-Set AllocationAbstract   In some use cases, e.g., Lightweight 4over6, the client may require   not just one port, but a port set.  This document defines an   extension to the Port Control Protocol (PCP) that allows clients to   manipulate a set of ports as a whole.  This is accomplished using a   new MAP option: PORT_SET.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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7753.Sun, et al.                  Standards Track                    [Page 1]

RFC 7753                      PCP PORT_SET                 February 2016Copyright Notice   Copyright (c) 2016 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.Sun, et al.                  Standards Track                    [Page 2]

RFC 7753                      PCP PORT_SET                 February 2016Table of Contents1. Introduction ....................................................41.1. Applications Using Port Sets ...............................41.2. Lightweight 4over6 .........................................41.3. Firewall Control ...........................................41.4. Discovering Stateless Port-Set Mappings ....................52. The Need for PORT_SET ...........................................53. Terminology .....................................................64. The PORT_SET Option .............................................64.1. Client Behavior ............................................84.2. Server Behavior ............................................84.3. Absence of Capability Discovery ............................94.4. Port-Set Renewal and Deletion .............................104.4.1. Overlap Conditions .................................105. Examples .......................................................10      5.1. Simple Request on Network Address Translator           IPv4/IPv4 (NAT44) .........................................105.2. Stateless Mapping Discovery ...............................125.3. Resolving Overlap .........................................136. Operational Considerations .....................................136.1. Limits and Quotas .........................................136.2. High Availability .........................................136.3. Idempotence ...............................................13      6.4. What should a PCP client do when it receives fewer           ports than requested? .....................................157. Security Considerations ........................................158. IANA Considerations ............................................169. References .....................................................169.1. Normative References ......................................169.2. Informative References ....................................16   Acknowledgements ..................................................17   Contributors ......................................................17   Authors' Addresses ................................................18Sun, et al.                  Standards Track                    [Page 3]

RFC 7753                      PCP PORT_SET                 February 20161.  Introduction   This document extends the Port Control Protocol (PCP) [RFC6887] with   the ability to retrieve a set of ports using a single request.  It   does so by defining a new PORT_SET option.   This section describes a few of the possible envisioned use cases.   Note that the PCP extension defined in this document is generic and   is expected to be applicable to other use cases.1.1.  Applications Using Port Sets   Some applications require not just one port, but a port set.  One   example is a Session Initiation Protocol (SIP) User Agent Server   (UAS) [RFC3261] expecting to handle multiple concurrent calls,   including media termination.  When the UAS receives a call, it needs   to signal media port numbers to its peer.  Generating individual PCP   MAP requests for each of the media ports during call setup would   introduce unwanted latency and increased signaling load.  Instead,   the server can pre-allocate a set of ports such that no PCP exchange   is needed during call setup.1.2.  Lightweight 4over6   In the Lightweight 4over6 (lw4o6) [RFC7596] architecture, shared   global addresses can be allocated to customers.  This allows moving   the Network Address Translation (NAT) function, otherwise   accomplished by a Carrier-Grade NAT (CGN) [RFC6888], to the Customer   Premises Equipment (CPE).  This provides more control over the NAT   function to the user, and more scalability to the Internet Service   Provider (ISP).   In the lw4o6 architecture, the PCP-controlled device corresponds to   the Lightweight Address Family Transition Router (lwAFTR), and the   PCP client corresponds to the Lightweight B4 (lwB4).  The PCP client   sends a PCP MAP request containing a PORT_SET option to trigger   shared address allocation on the Lightweight AFTR (lwAFTR).  The PCP   response contains the shared address information, including the port   set allocated to the Lightweight B4 (lwB4).1.3.  Firewall Control   Port sets are often used in firewall rules.  For example, defining a   range for Real-time Transport Protocol (RTP) [RFC3550] traffic is   common practice.  The PCP MAP request can already be used for   firewall control.  The PORT_SET option brings the additional ability   to manipulate firewall rules operating on port sets instead of single   ports.Sun, et al.                  Standards Track                    [Page 4]

RFC 7753                      PCP PORT_SET                 February 20161.4.  Discovering Stateless Port-Set Mappings   A PCP MAP request can be used to retrieve a mapping from a stateless   device (i.e., one that does not establish any per-flow state, and   simply rewrites the address and/or port in a purely algorithmic   fashion, including no rewriting).  Similarly, a PCP MAP request with   a PORT_SET request can be used to discover a port-set mapping from a   stateless device.  SeeSection 5.2 for an example.2.  The Need for PORT_SET   Multiple PCP MAP requests can be used to manipulate a set of ports;   this has roughly the same effect as a single use of a PCP MAP request   with a PORT_SET option.  However, use of the PORT_SET option is more   efficient when considering the following aspects:   Network Traffic:  A single request uses fewer network resources than      multiple requests.   Latency:  Even though PCP MAP requests can be sent in parallel, we      can expect the total processing time to be longer for multiple      requests than for a single one.   Server-side efficiency:  Some PCP-controlled devices can allocate      port sets in a manner such that data passing through the device is      processed much more efficiently than the equivalent using      individual port allocations.  For example, a CGN having a "bulk"      port allocation scheme (see[RFC6888], Section 5) often has this      property.   Server-side scalability:  The number of state table entries in PCP-      controlled devices is often a limiting factor.  Allocating port      sets in a single request can result in a single mapping entry      being used, therefore allowing greater scalability.   Therefore, while it is functionally possible to obtain the same   results using plain MAP, the extension proposed in this document   allows greater efficiency, scalability, and simplicity, while   lowering latency and necessary network traffic.   In addition, PORT_SET supports parity preservation.  Some protocols   (e.g., RTP [RFC3550]) assign meaning to a port number's parity.  When   mapping sets of ports for the purpose of using such kind of protocol,   preserving parity can be necessary.Sun, et al.                  Standards Track                    [Page 5]

RFC 7753                      PCP PORT_SET                 February 20163.  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].4.  The PORT_SET Option   Option Name:  PORT_SET   Number:  130 (seeSection 8)   Purpose:  To map sets of ports.   Valid for Opcodes:  MAP   Length:  5 bytes   May appear in:  Both requests and responses   Maximum occurrences:  1   The PORT_SET option indicates that the PCP client wishes to reserve a   set of ports.  The requested number of ports in that set is indicated   in the option.   The maximum occurrences of the PORT_SET option MUST be limited to 1.   The reason is that the Suggested External Port Set depends on the   data contained in the MAP Opcode header.  Having two PORT_SET options   with a single MAP Opcode header would imply having two overlapping   Suggested External Port Sets.   Note that the option number is in the "optional to process" range   (128-191), meaning that a PCP MAP request with a PORT_SET option will   be interpreted by a PCP server that does not support PORT_SET as a   single-port PCP MAP request, as if the PORT_SET option was absent.   The PORT_SET option is formatted as shown in Figure 1.Sun, et al.                  Standards Track                    [Page 6]

RFC 7753                      PCP PORT_SET                 February 2016    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=130|   Reserved    |        Option Length=5        |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |        Port Set Size          |      First Internal Port      |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |  Reserved   |P|   +-+-+-+-+-+-+-+-+                         Figure 1: PORT_SET Option   The fields are as follows:   Port Set Size:  A 16-bit unsigned integer.  Number of ports      requested.  MUST NOT be zero.   First Internal Port:  In a request, this field MUST be set equal to      the Internal Port field in the MAP Opcode by the PCP client.  In a      response, this field indicates the First Internal Port of the port      set mapped by the PCP server, which may differ from the value sent      in the request.  That is to be contrasted to the Internal Port      field, which by necessity is always identical in matched requests      and responses.   Reserved:  MUST be set to zero when sending; MUST be ignored when      receiving.   P (parity bit):  1 if parity preservation is requested; 0 otherwise.      See[RFC4787], Section 4.2.2.   Note that Option Code, Reserved, and Option Length are as described   in[RFC6887], Section 7.3.   The Internal Port Set is defined as being the range of Port Set Size   ports starting from the First Internal Port.  The Suggested External   Port Set is defined as being the range of Port Set Size ports   starting from the Suggested External Port.  Similarly, the Assigned   External Port Set is defined as being the range of Port Set Size   ports starting from the Assigned External Port.  The Internal Port   Set returned in a response and the Assigned External Port Set have   the same size.   The Suggested External Port corresponds to the first port in the   Suggested External Port Set.  Its purpose is for clients to be able   to regenerate previous mappings after state loss.  When such an event   happens, clients may attempt to regenerate identical mappings bySun, et al.                  Standards Track                    [Page 7]

RFC 7753                      PCP PORT_SET                 February 2016   suggesting the same External Port Set as before the state loss.  Note   that there is no guarantee that the allocated External Port Set will   be the one suggested by the client.4.1.  Client Behavior   To retrieve a set of ports, the PCP client adds a PORT_SET option to   its PCP MAP request.  If parity preservation is required (i.e., an   even port to be mapped to an even port and an odd port to be mapped   to an odd port), the PCP client MUST set the parity bit (to 1) to ask   the PCP server to preserve the port parity.   The PCP client MUST NOT include more than one PORT_SET option in a   PCP MAP request.  If several port sets are needed, the PCP client   MUST issue separate PCP MAP requests, each potentially including a   PORT_SET option.  These individual PCP MAP requests MUST include   distinct Internal Ports.   If the PCP client does not know the exact number of ports it   requires, it MAY then set the Port Set Size to 0xffff, indicating   that it is willing to accept as many ports as the PCP server can   offer.   A PCP client SHOULD NOT send a PORT_SET option for single-port PCP   MAP requests (including creation, renewal, and deletion), because   that needlessly increases processing on the server.   PREFER_FAILURE MUST NOT appear in a request with a PORT_SET option.   As a reminder, PREFER_FAILURE was specifically designed for the   Universal Plug and Play (UPnP) Internet Gateway Device - Port Control   Protocol Interworking Function (IGD-PCP IWF) [RFC6970].  The reasons   for not recommending the use of PREFER_FAILURE are discussed inSection 13.2 of [RFC6887].   When the PCP-controlled device supports delegation of multiple port   sets for a given PCP client, the PCP client MAY re-initiate a PCP   request to get another port set when it has exhausted all the ports   within the port set.4.2.  Server Behavior   In addition to regular PCP MAP request processing, the following   checks are made upon receipt of a PORT_SET option with a non-zero   Requested Lifetime:   o  If multiple PORT_SET options are present in a single PCP MAP      request, a MALFORMED_OPTION error is returned.Sun, et al.                  Standards Track                    [Page 8]

RFC 7753                      PCP PORT_SET                 February 2016   o  If the Port Set Size is zero, a MALFORMED_OPTION error is      returned.   o  If a PREFER_FAILURE option is present, a MALFORMED_OPTION error is      returned.   The PCP server MAY map fewer ports than the value of Port Set Size   from the request.  It MUST NOT map more ports than the PCP client   asked for.  Internal Ports outside the range of Port Set Size ports   starting from the Internal Port MUST NOT be mapped by the PCP server.   If the requested port set cannot be fully satisfied, the PCP server   SHOULD map as many ports as possible and SHOULD map at least one port   (which is the same behavior as if Port Set Size is set to 1).   If the PCP server ends up mapping only a single port, for any reason,   the PORT_SET option MUST NOT be present in the response.  In   particular, if the PCP server receives a single-port PCP MAP request   that includes a PORT_SET option, the PORT_SET option is silently   ignored, and the request is handled as a single-port PCP MAP request.   If the port parity preservation is requested (P = 1), the PCP server   MAY preserve port parity.  In that case, the External Port is set to   a value having the same parity as the First Internal Port.   If the mapping is successful, the MAP response's Assigned External   Port is set to the first port in the External Port Set, and the   PORT_SET option's Port Set Size is set to the number of ports in the   mapped port set.  The First Internal Port field is set to the first   port in the Internal Port Set.4.3.  Absence of Capability Discovery   A PCP client that wishes to make use of a port set includes the   PORT_SET option.  If no PORT_SET option is present in the response,   the PCP client cannot conclude that the PCP server does not support   the PORT_SET option.  It may just be that the PCP server does support   PORT_SET but decided to allocate only a single port, for reasons that   are its own.  If the client wishes to obtain more ports, it MAY send   additional PCP MAP requests (seeSection 6.4), which the PCP server   may or may not grant according to local policy.   If port-set capability is added to or removed from a running PCP   server, the server MAY reset its Epoch time and send an ANNOUNCE   message as described in the PCP specification ([RFC6887],   Section 14.1).  This causes PCP clients to retry, and those using   PORT_SET will now receive a different response.Sun, et al.                  Standards Track                    [Page 9]

RFC 7753                      PCP PORT_SET                 February 20164.4.  Port-Set Renewal and Deletion   Port-set mappings are renewed and deleted as a single entity.  That   is, the lifetime of all port mappings in the set is set to the   Assigned Lifetime at once.   A PCP client attempting to refresh or delete a port-set mapping MUST   include the PORT_SET option in its request.4.4.1.  Overlap Conditions   Port-set PCP MAP requests can overlap with existing single-port or   port-set mappings.  This can happen either by mistake or after a PCP   client becomes out of sync with server state.   If a PCP server receives a PCP MAP request, with or without a   PORT_SET option, that tries to map one or more Internal Ports or port   sets belonging to already-existing mappings, then the request is   considered to be a refresh request applying those mappings.  Each of   the matching port or port-set mappings is processed independently, as   if a separate refresh request had been received.  The processing is   as described inSection 15 of [RFC6887].  The PCP server sends a   Mapping Update message for each of the mappings.5.  Examples5.1.  Simple Request on Network Address Translator IPv4/IPv4 (NAT44)   An application requires a range of 100 IPv4 UDP ports to be mapped to   itself.  The application running on the host has created sockets   bound to IPv4 UDP ports 50,000 to 50,099 for this purpose.  It does   not care about which External Port numbers are allocated.  The PCP   client sends a PCP request with the following parameters over IPv4:   o  MAP Opcode      Mapping Nonce:  <a random nonce>      Protocol:  17      Internal Port:  50,000      Suggested External Port:  0      Suggested External IP Address:  ::ffff:0.0.0.0Sun, et al.                  Standards Track                   [Page 10]

RFC 7753                      PCP PORT_SET                 February 2016   o  PORT_SET Option      Port Set Size:  100      First Internal Port:  50,000      P: 0   The PCP server is unable to fulfill the request fully: it is   configured by local policy to only allocate 32 ports per user.  Since   the PREFER_FAILURE option is absent from the request, it decides to   map UDP ports 37,056 to 37,087 on external address 192.0.2.3 to   Internal Ports 50,000 to 50,031.  After setting up the mapping in the   NAT44 device it controls, it replies with the following PCP response:   o  MAP Opcode      Mapping Nonce:  <copied from the request>      Protocol:  17      Internal Port:  50,000      Assigned External Port:  37,056      Assigned External IP Address:  ::ffff:192.0.2.3   o  PORT_SET Option      Port Set Size:  32      First Internal Port:  50,000      P: 0   Upon receiving this response, the host decides that 32 ports is good   enough for its purposes.  It closes sockets bound to ports 50,032 to   50,099, sets up a refresh timer, and starts using the port range it   has just been assigned.Sun, et al.                  Standards Track                   [Page 11]

RFC 7753                      PCP PORT_SET                 February 20165.2.  Stateless Mapping Discovery   A host wants to discover a stateless NAT44 mapping pointing to it.   To do so, it sends the following request over IPv4:   o  MAP Opcode      Mapping Nonce:  <a random nonce>      Protocol:  0      Internal Port:  1      Suggested External Port:  0      Suggested External IP Address:  ::ffff:0.0.0.0   o  PORT_SET Option      Port Set Size:  65,535      First Internal Port:  1      P: 0   The PCP server sends the following response:   o  MAP Opcode      Mapping Nonce:  <copied from the request>      Protocol:  0      Internal Port:  1      Assigned External Port:  26,624      Assigned External IP Address:  ::ffff:192.0.2.5   o  PORT_SET Option      Port Set Size:  2048      First Internal Port:  26,624      P: 0Sun, et al.                  Standards Track                   [Page 12]

RFC 7753                      PCP PORT_SET                 February 2016   From this response, the host understands that a 2048-port stateless   mapping is pointing to itself, starting from port 26,624 on external   IP address 192.0.2.5.5.3.  Resolving Overlap   This example relates toSection 4.4.1.   Suppose Internal Port 100 is mapped to External Port 100 and port set   101-199 is mapped to External Port Set 201-299.  The PCP server   receives a PCP MAP request with Internal Port = 100, External Port =   0, and a PORT_SET option with Port Set Size = 100.  The request's   Mapping Nonce is equal to those of the existing single-port and port-   set mappings.  This request is therefore treated as two refresh   requests, the first one applying to the single-port mapping and the   second one applying to the port-set mapping.  The PCP server updates   the lifetimes of both mappings as usual and then sends two responses:   the first one contains Internal Port = 100, External Port = 100, and   no PORT_SET option, while the second one contains Internal Port =   101, External Port = 201, and a PORT_SET option with Port Set Size =   99.6.  Operational Considerations6.1.  Limits and Quotas   It is up to the PCP server to determine the port-set quota, if any,   for each PCP client.   If the PCP server is configured to allocate multiple port-set   allocations for one subscriber, the same Assigned External IP Address   SHOULD be assigned to the subscriber in multiple port-set responses.   To optimize the number of mapping entries maintained by the PCP   server, it is RECOMMENDED to configure the PCP server to assign the   maximum allowed Port Set Size in a single response.  This policy   SHOULD be configurable.6.2.  High Availability   The failover mechanism in MAP (Section 14 of [RFC6887]) can also be   applied to port sets.6.3.  Idempotence   A core, desirable property of PCP is idempotence.  In a nutshell,   requests produce the same results whether they are executed once or   multiple times.  This property is preserved with the PORT_SET option,Sun, et al.                  Standards Track                   [Page 13]

RFC 7753                      PCP PORT_SET                 February 2016   with the following caveat: the order in which the PCP server receives   requests with overlapping Internal Port Sets will affect the mappings   being created and the responses received.   For example, suppose these two requests are sent by a PCP client:   Request A:  Internal Port Set 1-10   Request B:  Internal Port Set 5-14   The PCP server's actions will depend on which request is received   first.  Suppose that A is received before B:   Upon reception of A:  Internal Ports 1-10 are mapped.  A success      response containing the following fields is sent:      Internal Port:  1      First Internal Port:  1      Port Set Size:  10   Upon reception of B:  The request matches mapping A.  The request is      interpreted as a refresh request for mapping A, and a response      containing the following fields is sent:      Internal Port:  5      First Internal Port:  1      Port Set Size:  10   If the order of reception is reversed (B before A), the created   mapping will be different, and the First Internal Port in both   responses would then be 5.   To avoid surprises, PCP clients MUST ensure that port-set mapping   requests do not inadvertently overlap.  For example, a host's   operating system could include a central PCP client process through   which port-set mapping requests would be arbitrated.  Alternatively,   individual PCP clients running on the same host would be required to   acquire the Internal Ports from the operating system (e.g., a call to   the bind() function from the BSD API) before trying to map them with   PCP.Sun, et al.                  Standards Track                   [Page 14]

RFC 7753                      PCP PORT_SET                 February 20166.4.  What should a PCP client do when it receives fewer ports than      requested?   Suppose a PCP client asks for 16 ports and receives 8.  What should   it do?  Should it consider this a final answer?  Should it try a   second request, asking for 8 more ports?  Should it fall back to 8   individual PCP MAP requests?  This document leaves the answers to be   implementation specific but describes issues to be considered when   answering them.   First, the PCP server has decided to allocate 8 ports for some   reason.  It may be that allocation sizes have been limited by the PCP   server's administrator.  It may be that the PCP client has reached a   quota.  It may be that these 8 ports were the last contiguous ones   available.  Depending on the reason, asking for more ports may or may   not be likely to actually yield more ports.  However, the PCP client   has no way of knowing.   Second, not all PCP clients asking for N ports actually need all N   ports to function correctly.  For example, a DNS resolver could ask   for N ports to be used for source-port randomization.  If fewer than   N ports are received, the DNS resolver will still work correctly, but   source-port randomization will be slightly less efficient, having   fewer bits to play with.  In that case, it would not make much sense   to ask for more ports.   Finally, asking for more ports could be considered abuse.  External   Ports are a resource that is to be shared among multiple PCP clients.   A PCP client trying to obtain more than its fair share could trigger   countermeasures according to local policy.   In conclusion, it is expected that, for most applications, asking for   more ports would not yield benefits justifying the additional costs.7.  Security Considerations   The security considerations discussed in [RFC6887] apply to this   extension.   As described inSection 4.4.1, a single PCP request using the   PORT_SET option may result in multiple responses.  For this to   happen, it is necessary that the request contain the nonce associated   with multiple mappings on the server.  Therefore, an on-path attacker   could use an eavesdropped nonce to mount an amplification attack.   Use of PCP authentication ([RFC6887], Section 18) eliminates this   attack vector.Sun, et al.                  Standards Track                   [Page 15]

RFC 7753                      PCP PORT_SET                 February 2016   In order to prevent a PCP client from controlling all ports bound to   a shared IP address, port quotas should be configured on the PCP   server (Section 17.2 of [RFC6887]).8.  IANA Considerations   IANA has allocated value 130 in the "PCP Options" registry at   <http://www.iana.org/assignments/pcp-parameters> for the new PCP   option defined inSection 4.9.  References9.1.  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>.   [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>.9.2.  Informative References   [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>.   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.              Jacobson, "RTP: A Transport Protocol for Real-Time              Applications", STD 64,RFC 3550, DOI 10.17487/RFC3550,              July 2003, <http://www.rfc-editor.org/info/rfc3550>.   [RFC4787]  Audet, F., Ed. and C. Jennings, "Network Address              Translation (NAT) Behavioral Requirements for Unicast              UDP",BCP 127,RFC 4787, DOI 10.17487/RFC4787, January              2007, <http://www.rfc-editor.org/info/rfc4787>.   [RFC6888]  Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa,              A., and H. Ashida, "Common Requirements for Carrier-Grade              NATs (CGNs)",BCP 127,RFC 6888, DOI 10.17487/RFC6888,              April 2013, <http://www.rfc-editor.org/info/rfc6888>.Sun, et al.                  Standards Track                   [Page 16]

RFC 7753                      PCP PORT_SET                 February 2016   [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>.   [RFC7596]  Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I.              Farrer, "Lightweight 4over6: An Extension to the Dual-              Stack Lite Architecture",RFC 7596, DOI 10.17487/RFC7596,              July 2015, <http://www.rfc-editor.org/info/rfc7596>.Acknowledgements   The authors would like to express sincere appreciation to Alain   Durand, Cong Liu, Dan Wing, Dave Thaler, Peter Koch, Reinaldo Penno,   Sam Hartman, Stuart Cheshire, Ted Lemon, Yoshihiro Ohba, Meral   Shirazipour, Jouni Korhonen, and Ben Campbell for their useful   comments and suggestions.Contributors   The following individuals contributed to this document:   Yunqing Chen   China Telecom   Room 502, No.118, Xizhimennei Street   Beijing 100035   China   Chongfeng Xie   China Telecom   Room 502, No.118, Xizhimennei Street   Beijing 100035   China   Yong Cui   Tsinghua University   Beijing 100084   China   Phone: +86-10-62603059   Email: yong@csnet1.cs.tsinghua.edu.cnSun, et al.                  Standards Track                   [Page 17]

RFC 7753                      PCP PORT_SET                 February 2016   Qi Sun   Tsinghua University   Beijing 100084   China   Phone: +86-10-62785822   Email: sunqibupt@gmail.com   Gabor Bajko   Mediatek Inc.   Email: gabor.bajko@mediatek.com   Xiaohong Deng   France Telecom   Email: xiaohong.deng@orange-ftgroup.comAuthors' Addresses   Qiong Sun   China Telecom   China   Phone: 86 10 58552936   Email: sunqiong@ctbri.com.cn   Mohamed Boucadair   France Telecom   Rennes  35000   France   Email: mohamed.boucadair@orange.com   Senthil Sivakumar   Cisco Systems   7100-8 Kit Creek Road   Research Triangle Park, NC  27709   United States   Phone: +1 919 392 5158   Email: ssenthil@cisco.comSun, et al.                  Standards Track                   [Page 18]

RFC 7753                      PCP PORT_SET                 February 2016   Cathy Zhou   Huawei Technologies   Bantian, Longgang District   Shenzhen  518129   China   Email: cathy.zhou@huawei.com   Tina Tsou   Philips Lighting   3 Burlington Woods Dr #4t   Burlington, MA  01803   United States   Phone: +1 617-423-9999   Email: tina.tsou@philips.com   Simon Perreault   Jive Communications   Quebec, QC   Canada   Email: sperreault@jive.comSun, et al.                  Standards Track                   [Page 19]

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