path: root/doc/rfc/rfc6970.txt

Internet Engineering Task Force (IETF)                      M. Boucadair
Request for Comments: 6970                                France Telecom
Category: Standards Track                                       R. Penno
ISSN: 2070-1721                                                  D. Wing
                                                                   Cisco
                                                               July 2013


                     Universal Plug and Play (UPnP)
 Internet Gateway Device - Port Control Protocol Interworking Function
                             (IGD-PCP IWF)

Abstract

   This document specifies the behavior of the Universal Plug and Play
   (UPnP) Internet Gateway Device - Port Control Protocol Interworking
   Function (IGD-PCP IWF).  A UPnP IGD-PCP IWF is required to be
   embedded in Customer Premises (CP) routers to allow for transparent
   NAT control in environments where a UPnP IGD is used on the LAN side
   and PCP is used on the external side of the CP router.

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/rfc6970.

















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Copyright Notice

   Copyright (c) 2013 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
      1.1. Requirements Language ......................................3
   2. Acronyms ........................................................4
   3. Architecture Model ..............................................4
   4. UPnP IGD-PCP IWF: Overview ......................................6
      4.1. UPnP IGD-PCP: State Variables ..............................6
      4.2. IGD-PCP: Methods ...........................................7
      4.3. UPnP IGD-PCP: Errors .......................................8
   5. Specification of the IGD-PCP IWF ................................9
      5.1. PCP Server Discovery .......................................9
      5.2. Control of the Firewall ...................................10
      5.3. Port Mapping Table ........................................10
      5.4. Interworking Function without NAT in the IGD ..............10
      5.5. NAT Embedded in the IGD ...................................11
      5.6. Creating a Mapping ........................................12
           5.6.1. AddAnyPortMapping() ................................12
           5.6.2. AddPortMapping() ...................................13
      5.7. Listing One or a Set of Mappings ..........................16
      5.8. Delete One or a Set of Mappings: DeletePortMapping() or
           DeletePortMappingRange() ..................................16
      5.9. Renewing a Mapping ........................................19
      5.10. Rapid Recovery ...........................................20
   6. Security Considerations ........................................21
   7. Acknowledgments ................................................21
   8. References .....................................................22
      8.1. Normative References ......................................22
      8.2. Informative References ....................................22







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1.  Introduction

   The Port Control Protocol (PCP) specification [RFC6887] discusses the
   implementation of NAT control features that rely upon Carrier Grade
   NAT devices such as a Dual-Stack Lite (DS-Lite) Address Family
   Transition Router (AFTR) [RFC6333] or NAT64 [RFC6146].  In
   environments where a Universal Plug and Play Internet Gateway Device
   (UPnP IGD) is used in the local network, an interworking function
   between the UPnP IGD and PCP is required to be embedded in the IGD
   (see the example illustrated in Figure 1).

                            UPnP IGD-PCP
   UPnP Control             Interworking
      Point                   Function                  PCP Server
        |                       IGD                          |
        |                        |                           |
        |  (1) AddPortMapping()  |                           |
        |----------------------->|                           |
        |                        |   (2) PCP MAP Request     |
        |                        |-------------------------->|
        |                        |                           |

                          Figure 1: Flow Example

   Two configurations are considered within this document:

   o  No NAT function is embedded in the IGD (Section 5.4).  This is
      required, for instance, in DS-Lite or NAT64 deployments.

   o  The IGD embeds a NAT function (Section 5.5).

   The UPnP IGD-PCP Interworking Function (UPnP IGD-PCP IWF) maintains a
   local mapping table that stores all active mappings constructed by
   internal IGD Control Points.  This design choice restricts the amount
   of PCP messages to be exchanged with the PCP server.

   Triggers for deactivating the UPnP IGD-PCP IWF from the IGD and
   relying on a PCP-only mode are out of scope for this document.

   Considerations related to co-existence of the UPnP IGD-PCP
   Interworking Function and a PCP Proxy [PCP-PROXY] are out of scope.

1.1.  Requirements Language

   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].




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2.  Acronyms

   This document makes use of the following abbreviations:

      DS-Lite - Dual-Stack Lite
      IGD - Internet Gateway Device
      IGD:1 - UPnP Forum's nomenclature for version 1 of IGD [IGD1]
      IGD:2 - UPnP Forum's nomenclature for version 2 of IGD [IGD2]
      IWF - Interworking Function
      NAT - Network Address Translation
      PCP - Port Control Protocol
      UPnP - Universal Plug and Play

3.  Architecture Model

   As a reminder, Figure 2 illustrates the architecture model as adopted
   by the UPnP Forum [IGD2].  In Figure 2, the following UPnP
   terminology is used:

   o  'Client' refers to a host located in the local network.

   o  'IGD Control Point' is a device using UPnP to control an IGD
      (Internet Gateway Device).

   o  'IGD' is a router supporting a UPnP IGD.  It is typically a NAT or
      a firewall.

   o  'Host' is a remote peer reachable in the Internet.

                +-------------+
                | IGD Control |
                |   Point     |-----+
                +-------------+     |   +-----+       +------+
                                    +---|     |       |      |
                                        | IGD |-------| Host |
                                    +---|     |       |      |
                +-------------+     |   +-----+       +------+
                |   Client    |-----+
                +-------------+

                         Figure 2: UPnP IGD Model

   This model is not valid when PCP is used to control, for instance, a
   Carrier Grade NAT (aka Provider NAT) while internal hosts continue to
   use a UPnP IGD.  In such scenarios, Figure 3 shows the updated model.






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   +-------------+
   | IGD Control |
   |   Point     |----+
   +-------------+    |   +-----+      +--------+               +------+
                      +---| IGD-|      |Provider|               |Remote|
                          | PCP |------|  NAT   |--<Internet>---| Host |
                      +---| IWF |      |        |               |      |
   +-------------+    |   +-----+      +--------+               +------+
   | Local Host  |----+
   +-------------+
                        LAN Side  External Side
   <======UPnP IGD==============><=====PCP=====>

                 Figure 3: UPnP IGD-PCP Interworking Model

   In the updated model depicted in Figure 3, one or two levels of NAT
   can be encountered in the data path.  Indeed, in addition to the
   Carrier Grade NAT, the IGD may embed a NAT function (Figure 4).

   +-------------+
   | IGD Control |
   |   Point     |----+
   +-------------+    |   +-----+      +--------+               +------+
                      +---| IGD-|      |Provider|               |Remote|
                          | PCP |------|  NAT   |--<Internet>---| Host |
                      +---| IWF |      |        |               |      |
   +-------------+    |   +-----+      +--------+               +------+
   | Local Host  |----+    NAT1           NAT2
   +-------------+

                      Figure 4: Cascaded NAT Scenario

   To ensure successful interworking between a UPnP IGD and PCP, an
   interworking function is embedded in the IGD.  In the model defined
   in Figure 3, all UPnP IGD server-oriented functions, a PCP client
   [RFC6887], and a UPnP IGD-PCP Interworking Function are embedded in
   the IGD.  In the rest of the document, "IGD-PCP IWF" refers to the
   UPnP IGD-PCP Interworking Function, which includes PCP client
   functionality.

   Without the involvement of the IGD-PCP IWF, the IGD Control Point
   would retrieve an external IP address and port number that have
   limited scope and that cannot be used to communicate with hosts
   located beyond NAT2 (i.e., assigned by the IGD, and not those
   assigned by NAT2 as depicted in Figure 4).

   The UPnP IGD-PCP IWF is responsible for generating a well-formed PCP
   message from a received UPnP IGD message, and vice versa.



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4.  UPnP IGD-PCP IWF: Overview

   Three tables are provided to specify the correspondence between a
   UPnP IGD and PCP:

   (1)  Section 4.1 provides the mapping between WANIPConnection state
        variables and PCP parameters;

   (2)  Section 4.2 focuses on the correspondence between supported
        methods;

   (3)  Section 4.3 lists the PCP error messages and their corresponding
        IGD error messages.

   Note that some enhancements have been integrated in WANIPConnection,
   as documented in [IGD2].

4.1.  UPnP IGD-PCP: State Variables

   Below are listed only the UPnP IGD state variables applicable to the
   IGD-PCP IWF:

   ExternalIPAddress:  External IP Address
      Read-only variable with the value from the last PCP response, or
      the empty string if none was received yet.  This state is stored
      on a per-IGD-Control-Point basis.

   PortMappingNumberOfEntries:  Managed locally by the UPnP IGD-PCP IWF.

   PortMappingEnabled:
      PCP does not support deactivating the dynamic NAT mapping, since
      the initial goal of PCP is to ease the traversal of Carrier Grade
      NAT.  Supporting such per-subscriber function may overload the
      Carrier Grade NAT.
      Only "1" is allowed: i.e., the UPnP IGD-PCP Interworking Function
      MUST send back an error if a value different from 1 is signaled.

   PortMappingLeaseDuration:  Requested Mapping Lifetime
      In IGD:1 [IGD1], the value 0 means infinite; in IGD:2, it is
      remapped to the IGD maximum of 604800 seconds [IGD2].  PCP allows
      for a maximum value of 4294967296 seconds.
      The UPnP IGD-PCP Interworking Function simulates long and even
      infinite lifetimes using renewals (see Section 5.9).  The behavior
      of the UPnP IGD-PCP IWF in the case of a failing renewal is
      currently undefined (see Section 5.9).






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      IGD:1 doesn't define the behavior in the case of state loss; IGD:2
      doesn't require that state be kept in stable storage, i.e., to
      allow the state to survive resets/reboots.  The UPnP IGD-PCP
      Interworking Function MUST support IGD:2 behavior.

   RemoteHost:  Remote Peer IP Address
      Note that IGD:2 allows a domain name, which has to be resolved to
      an IP address.  Mapped to the Remote Peer IP Address field of the
      FILTER option.

   ExternalPort:  External Port Number
      Mapped to the Suggested External Port field in MAP messages.

   InternalPort:  Internal Port Number
      Mapped to the Internal Port field in MAP messages.

   PortMappingProtocol:  Protocol
      Mapped to the Protocol field in MAP messages.  Note that a UPnP
      IGD only supports TCP and UDP.

   InternalClient:  Internal IP Address
      Note that IGD:2 allows a domain name, which has to be resolved to
      an IP address.  Mapped to the Internal IP Address field of the
      THIRD_PARTY option.

   PortMappingDescription:  Not supported in base PCP.
      If the local PCP client supports a PCP option to convey the
      description (e.g., [PCP-DESCR-OPT]), this option SHOULD be used to
      relay the mapping description.

   SystemUpdateID (IGD:2 only):  Managed locally by the UPnP IGD-PCP
      IWF.

   A_ARG_TYPE_PortListing (IGD:2 only):  Managed locally by the UPnP
      IGD-PCP IWF.

4.2.  IGD-PCP: Methods

   IGD:1 and IGD:2 methods applicable to the UPnP IGD-PCP Interworking
   Function are both listed here.

   GetGenericPortMappingEntry():  This request is not relayed to the PCP
      server.

      The IGD-PCP Interworking Function maintains a list of active
      mappings instantiated in the PCP server by internal hosts.  See
      Section 5.7 for more information.




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   GetSpecificPortMappingEntry():  MAP with PREFER_FAILURE option.

      This request is relayed to the PCP server by issuing a MAP request
      with the PREFER_FAILURE option.  It is RECOMMENDED to use a short
      lifetime (e.g., 60 seconds).

   AddPortMapping():  MAP
      See Section 5.6.2.

   AddAnyPortMapping() (IGD:2 only):  MAP
      See Section 5.6.1.

   DeletePortMapping():  MAP with Requested Lifetime set to 0.
      See Section 5.8.

   DeletePortMappingRange() (IGD:2 only):  MAP with Requested Lifetime
      set to 0.
      Individual requests are issued by the IGD-PCP IWF.  See
      Section 5.8 for more details.

   GetExternalIPAddress():  MAP
      This can be learned from any active mapping.  If there are no
      active mappings, the IGD-PCP IWF MAY request a short-lived mapping
      (e.g., to the Discard service (TCP/9 or UDP/9) or some other
      port).  However, once that mapping expires, a subsequent implicit
      or explicit dynamic mapping might be mapped to a different
      external IP address.  See Section 11.6 of [RFC6887] for more
      discussion.

   GetListOfPortMappings():  See Section 5.7 for more information.
      The IGD-PCP Interworking Function maintains a list of active
      mappings instantiated in the PCP server.  The IGD-PCP Interworking
      Function handles this request locally.

4.3.  UPnP IGD-PCP: Errors

   This section lists PCP error codes and the corresponding UPnP IGD
   codes.  Error codes specific to IGD:2 are tagged accordingly.

   1 UNSUPP_VERSION:  501 "ActionFailed"

   2 NOT_AUTHORIZED:  IGD:1 718 "ConflictInMappingEntry" / IGD:2 606
      "Action not authorized"

   3 MALFORMED_REQUEST:  501 "ActionFailed"






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   4 UNSUPP_OPCODE:  501 "ActionFailed"
      [RFC6887] allows the PCP server to be configured to disable
      support for the MAP Opcode, but the IGD-PCP IWF cannot work in
      this situation.

   5 UNSUPP_OPTION:  501 "ActionFailed"
      This error code can be received if PREFER_FAILURE is not supported
      on the PCP server.  Note that PREFER_FAILURE is not mandatory to
      support, but AddPortMapping() cannot be implemented without it.

   6 MALFORMED_OPTION:  501 "ActionFailed"

   7 NETWORK_FAILURE:  501 "ActionFailed"

   8 NO_RESOURCES:  IGD:1 501 "ActionFailed" / IGD:2 728
      "NoPortMapsAvailable"
      Cannot be distinguished from USER_EX_QUOTA.

   9 UNSUPP_PROTOCOL:  501 "ActionFailed"

   10 USER_EX_QUOTA:  IGD:1 501 "ActionFailed" / IGD:2 728
      "NoPortMapsAvailable"
      Cannot be distinguished from NO_RESOURCES.

   11 CANNOT_PROVIDE_EXTERNAL:  718 "ConflictInMappingEntry" (see
      Section 5.6.2) or 714 "NoSuchEntryInArray" (see Section 5.8).

   12 ADDRESS_MISMATCH:  501 "ActionFailed"

   13 EXCESSIVE_REMOTE_PEERS:  501 "ActionFailed"

5.  Specification of the IGD-PCP IWF

   This section covers scenarios with or without NAT in the IGD.

   This specification assumes that the PCP server is configured to
   accept the MAP Opcode.

   The IGD-PCP IWF handles the "Mapping Nonce" the same way as any PCP
   client [RFC6887].

5.1.  PCP Server Discovery

   The IGD-PCP IWF implements one of the discovery methods identified in
   [RFC6887] (e.g., DHCP [PCP-DHCP-OPT]).  The IGD-PCP Interworking
   Function behaves as a PCP client when communicating with provisioned
   PCP server(s).




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   If no IPv4 address/IPv6 prefix is assigned to the IGD or the IGD is
   unable to determine whether it should contact an upstream PCP server,
   the IGD-PCP Interworking Function MUST NOT be invoked.

   If the IGD determines that it should establish communication with an
   upstream PCP server (e.g., because of DHCP configuration or having
   previously communicated with a PCP server), a "501 ActionFailed"
   error message is returned to the requesting IGD Control Point if the
   IGD-PCP IWF fails to establish communication with that PCP server.
   Note that the IGD-PCP IWF proceeds to PCP message validation and
   retransmission the same way as any PCP client [RFC6887].

5.2.  Control of the Firewall

   In order to configure security policies to be applied to inbound and
   outbound traffic, a UPnP IGD can be used to control a local firewall
   engine.  No IGD-PCP IWF is therefore required for that purpose.

   The use of the IGD-PCP IWF to control an upstream PCP-controlled
   firewall is out of scope for this document.

5.3.  Port Mapping Table

   The IGD-PCP IWF MUST store locally all the mappings instantiated by
   internal IGD Control Points in the PCP server.  All mappings SHOULD
   be stored in permanent storage.

   Upon receipt of a PCP MAP response from the PCP server, the IGD-PCP
   Interworking Function MUST extract the enclosed mapping and MUST
   store it in the local mapping table.  The local mapping table is an
   image of the mapping table as maintained by the PCP server for a
   given subscriber.

   Each mapping entry stored in the local mapping table is associated
   with a lifetime as discussed in [RFC6887].  Additional considerations
   specific to the IGD-PCP Interworking Function are discussed in
   Section 5.9.

5.4.  Interworking Function without NAT in the IGD

   When no NAT is embedded in the IGD, the contents of received
   WANIPConnection and PCP messages are not altered by the IGD-PCP
   Interworking Function (i.e., the contents of WANIPConnection messages
   are mapped to PCP messages (and mapped back), according to
   Section 4.1).






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5.5.  NAT Embedded in the IGD

   When NAT is embedded in the IGD, the IGD-PCP IWF updates the contents
   of mapping messages received from the IGD Control Point.  These
   messages will contain an IP address and/or port number that belong to
   an internal host.  The IGD-PCP IWF MUST update such messages with the
   IP address and/or port number belonging to the external interface of
   the IGD (i.e., after the NAT1 operation as depicted in Figure 4).

   The IGD-PCP IWF intercepts all WANIPConnection messages issued by the
   IGD Control Point.  For each such message, the IGD-PCP IWF then
   generates one or more corresponding requests (see Sections 4.1, 4.2,
   and 4.3) and sends them to the provisioned PCP server.

   Each request sent by the IGD-PCP IWF to the PCP server MUST reflect
   the mapping information as enforced in the first NAT.  Particularly,
   the internal IP address and/or port number of the requests are
   replaced with the IP address and/or port number as assigned by the
   NAT of the IGD.  For the reverse path, the IGD-PCP IWF intercepts PCP
   response messages and generates WANIPConnection response messages.
   The contents of the generated WANIPConnection response messages are
   set as follows:

   o  The internal IP address and/or port number as initially set by the
      IGD Control Point and stored in the IGD NAT are used to update the
      corresponding fields in received PCP responses.

   o  The external IP address and port number are not altered by the
      IGD-PCP Interworking Function.

   o  The NAT mapping entry in the IGD is updated with the result of
      each PCP request.

   The lifetime of the mappings instantiated in the IGD SHOULD be the
   one assigned by the terminating PCP server.  In any case, the
   lifetime MUST NOT be lower than the one assigned by the terminating
   PCP server.














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5.6.  Creating a Mapping

   Two methods can be used to create a mapping: AddAnyPortMapping() and
   AddPortMapping().

5.6.1.  AddAnyPortMapping()

   When an IGD Control Point issues an AddAnyPortMapping() call, this
   request is received by the IGD.  The request is then relayed to the
   IGD-PCP IWF, which generates a PCP MAP request (see Section 4.1 for
   mapping between WANIPConnection and PCP parameters).

   If the IGD-PCP IWF fails to send the MAP request to its PCP server,
   it follows the behavior defined in Section 5.1.

   Upon receipt of a PCP MAP response from the PCP server, the
   corresponding UPnP IGD method is returned to the requesting IGD
   Control Point (the contents of the messages follow the
   recommendations listed in Section 5.5 or Section 5.4, according to
   the deployed scenario).  A flow example is depicted in Figure 5.

   If a PCP error is received from the PCP server, a corresponding
   WANIPConnection error code (see Section 4.3) is generated by the
   IGD-PCP IWF and sent to the requesting IGD Control Point.  If a
   short-lifetime error is returned (e.g., NETWORK_FAILURE,
   NO_RESOURCES), the PCP IWF MAY resend the same request to the PCP
   server after 30 seconds.  If a negative answer is received, the error
   is then relayed to the requesting IGD Control Point.

      Discussion: Some applications (e.g., uTorrent, Vuze, eMule) wait
      90 seconds or more for a response after sending a UPnP request.
      If a short-lifetime error occurs, resending the request may lead
      to a positive response from the PCP server.  IGD Control Points
      are therefore not aware of transient errors.

















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                               UPnP-PCP
   UPnP Control              Interworking
      Point                    Function                    PCP Server
        |                         |                             |
        | (1) AddAnyPortMapping() |                             |
        |    ExternalPort=8080    |                             |
        |------------------------>|                             |
        |                         |   (2) PCP MAP Request       |
        |                         |Suggested External Port=8080 |
        |                         |---------------------------->|
        |                         |                             |
        |                         |   (3) PCP MAP Response      |
        |                         | Assigned External Port=6598 |
        |                         |<----------------------------|
        | (4) AddAnyPortMapping() |                             |
        |    ReservedPort=6598    |                             |
        |<------------------------|                             |

                Figure 5: Flow Example: AddAnyPortMapping()

5.6.2.  AddPortMapping()

   A dedicated option called "PREFER_FAILURE" is defined in [RFC6887] to
   toggle the behavior in a PCP request message.  This option is
   inserted by the IGD-PCP IWF when issuing its requests to the PCP
   server only if a specific external port is requested by the IGD
   Control Point.

   Upon receipt of AddPortMapping() from an IGD Control Point, the
   IGD-PCP IWF MUST generate a PCP MAP request with all requested
   mapping information as indicated by the IGD Control Point if no NAT
   is embedded in the IGD or updated as specified in Section 5.5.  In
   addition, the IGD-PCP IWF MUST insert a PREFER_FAILURE option in the
   generated PCP request.

   If the IGD-PCP IWF fails to send the MAP request to its PCP server,
   it follows the behavior defined in Section 5.1.

   If the requested external port is not available, the PCP server will
   send a CANNOT_PROVIDE_EXTERNAL error response:

   1.  If a short-lifetime error is returned, the IGD-PCP IWF MAY resend
       the same request to the PCP server after 30 seconds without
       relaying the error to the IGD Control Point.  The IGD-PCP IWF MAY
       repeat this process until a positive answer is received or some
       maximum retry limit is reached.  When the maximum retry limit is
       reached, the IGD-PCP IWF relays a negative message to the IGD
       Control Point with ConflictInMappingEntry as the error code.



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       The maximum retry limit is implementation-specific; its default
       value is 2.

   2.  If a long-lifetime error is returned, the IGD-PCP IWF relays a
       negative message to the IGD Control Point with
       ConflictInMappingEntry as the error code.

   The IGD Control Point may issue a new request with a different
   requested external port number.  This process is typically repeated
   by the IGD Control Point until a positive answer is received or some
   maximum retry limit is reached.

   If the PCP server is able to create or renew a mapping with the
   requested external port, it sends a positive response to the IGD-PCP
   IWF.  Upon receipt of the response from the PCP server, the IGD-PCP
   IWF stores the returned mapping in its local mapping table and sends
   the corresponding positive answer to the requesting IGD Control
   Point.  This answer terminates the exchange.

   Figure 6 shows an example of the flow exchange that occurs when the
   PCP server satisfies the request from the IGD-PCP IWF.  Figure 7
   shows the message exchange when the requested external port is not
   available.

                              UPnP-PCP
   UPnP Control             Interworking
      Point                   Function                    PCP Server
        |                        |                             |
        |  (1) AddPortMapping()  |                             |
        |    ExternalPort=8080   |                             |
        |----------------------->|                             |
        |                        |   (2) PCP MAP Request       |
        |                        |Suggested External Port=8080 |
        |                        |       PREFER_FAILURE        |
        |                        |---------------------------->|
        |                        |                             |
        |                        |   (3) PCP MAP Response      |
        |                        | Assigned External Port=8080 |
        |                        |<----------------------------|
        |  (4) AddPortMapping()  |                             |
        |    ExternalPort=8080   |                             |
        |<-----------------------|                             |

                 Figure 6: Flow Example (Positive Answer)







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RFC 6970                    UPnP IGD-PCP IWF                   July 2013


                              UPnP-PCP
   UPnP Control             Interworking
      Point                   Function                    PCP Server
        |                        |                             |
        |  (1) AddPortMapping()  |                             |
        |    ExternalPort=8080   |                             |
        |----------------------->|                             |
        |                        |   (2) PCP MAP Request       |
        |                        |Suggested External Port=8080 |
        |                        |       PREFER_FAILURE        |
        |                        |---------------------------->|
        |                        |   (3) PCP MAP Response      |
        |                        |   CANNOT_PROVIDE_EXTERNAL   |
        |                        |<----------------------------|
        |      (4) Error:        |                             |
        | ConflictInMappingEntry |                             |
        |<-----------------------|                             |
        |  (5) AddPortMapping()  |                             |
        |    ExternalPort=5485   |                             |
        |----------------------->|                             |
        |                        |   (6) PCP MAP Request       |
        |                        |Suggested External Port=5485 |
        |                        |       PREFER_FAILURE        |
        |                        |---------------------------->|
        |                        |   (7) PCP MAP Response      |
        |                        |   CANNOT_PROVIDE_EXTERNAL   |
        |                        |<----------------------------|
        |      (8) Error:        |                             |
        | ConflictInMappingEntry |                             |
        |<-----------------------|                             |
                                 ....
        |  (a) AddPortMapping()  |                             |
        |    ExternalPort=6591   |                             |
        |----------------------->|                             |
        |                        |   (b) PCP MAP Request       |
        |                        |Suggested External Port=6591 |
        |                        |       PREFER_FAILURE        |
        |                        |---------------------------->|
        |                        |   (c) PCP MAP Response      |
        |                        |   CANNOT_PROVIDE_EXTERNAL   |
        |                        |<----------------------------|
        |      (d) Error:        |                             |
        | ConflictInMappingEntry |                             |
        |<-----------------------|                             |

                 Figure 7: Flow Example (Negative Answer)





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      Note: According to some experiments, some UPnP 1.0 Control Point
      implementations, e.g., uTorrent, simply try the same external port
      a number of times (usually 4 times) and then fail if the port is
      in use.  Also note that some applications use
      GetSpecificPortMappingEntry() to determine whether a mapping
      exists.

5.7.  Listing One or a Set of Mappings

   In order to list active mappings, an IGD Control Point may issue
   GetGenericPortMappingEntry(), GetSpecificPortMappingEntry(), or
   GetListOfPortMappings().

   GetGenericPortMappingEntry() and GetListOfPortMappings() methods MUST
   NOT be proxied to the PCP server, since a local mapping is maintained
   by the IGD-PCP IWF.

   Upon receipt of GetSpecificPortMappingEntry() from an IGD Control
   Point, the IGD-PCP IWF MUST check first to see if the external port
   number is used by the requesting IGD Control Point.  If the external
   port is already in use by the requesting IGD Control Point, the
   IGD-PCP IWF MUST send back the mapping entry matching the request.
   If not, the IGD-PCP IWF MUST relay to the PCP server a MAP request,
   with short lifetime (e.g., 60 seconds), including a PREFER_FAILURE
   option.  If the IGD-PCP IWF fails to send the MAP request to its PCP
   server, it follows the behavior defined in Section 5.1.  If the
   requested external port is in use, a PCP error message will be sent
   by the PCP server to the IGD-PCP IWF indicating
   CANNOT_PROVIDE_EXTERNAL as the error cause.  Then, the IGD-PCP IWF
   relays a negative message to the IGD Control Point.  If the port is
   not in use, the mapping will be created by the PCP server and a
   positive response will be sent back to the IGD-PCP IWF.  Once
   received by the IGD-PCP IWF, it MUST relay a negative message to the
   IGD Control Point indicating NoSuchEntryInArray as the error code so
   that the IGD Control Point knows the queried mapping doesn't exist.

5.8.  Delete One or a Set of Mappings: DeletePortMapping() or
      DeletePortMappingRange()

   An IGD Control Point requests the deletion of one or a list of
   mappings by issuing DeletePortMapping() or DeletePortMappingRange().

   In IGD:2, we assume that the IGD applies the appropriate security
   policies to determine whether a Control Point has the rights to
   delete one or a set of mappings.  When authorization fails, the "606
   Action Not Authorized" error code is returned to the requesting
   Control Point.




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RFC 6970                    UPnP IGD-PCP IWF                   July 2013


   When DeletePortMapping() or DeletePortMappingRange() is received by
   the IGD-PCP IWF, it first checks if the requested mappings to be
   removed are present in the local mapping table.  If no mapping
   matching the request is found in the local table, an error code is
   sent back to the IGD Control Point: "714 NoSuchEntryInArray" for
   DeletePortMapping() or "730 PortMappingNotFound" for
   DeletePortMappingRange().

   Figure 8 shows an example of an IGD Control Point asking to delete a
   mapping that is not instantiated in the local table of the IWF.

                               UPnP-PCP
   UPnP Control              Interworking
      Point                    Function                  PCP Server
        |                         |                           |
        | (1) DeletePortMapping() |                           |
        |------------------------>|                           |
        |                         |                           |
        |       (2) Error:        |                           |
        |    NoSuchEntryInArray   |                           |
        |<------------------------|                           |
        |                         |                           |

                   Figure 8: Local Delete (IGD-PCP IWF)

   If a mapping matches in the local table, a PCP MAP delete request is
   generated.  If no NAT is enabled in the IGD, the IGD-PCP IWF uses the
   input arguments as included in DeletePortMapping().  If a NAT is
   enabled in the IGD, the IGD-PCP IWF instead uses the corresponding IP
   address and port number as assigned by the local NAT.

   If the IGD-PCP IWF fails to send the MAP request to its PCP server,
   it follows the behavior defined in Section 5.1.

   When a positive answer is received from the PCP server, the IGD-PCP
   IWF updates its local mapping table (i.e., removes the corresponding
   entry) and notifies the IGD Control Point of the result of the
   removal operation.  Once the PCP MAP delete request is received by
   the PCP server, it removes the corresponding entry.  A PCP MAP
   SUCCESS response is sent back if the removal of the corresponding
   entry was successful; if not, a PCP error message containing the
   corresponding error cause (see Section 4.3) is sent back to the
   IGD-PCP IWF.








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RFC 6970                    UPnP IGD-PCP IWF                   July 2013


   If DeletePortMappingRange() is used, the IGD-PCP IWF does a lookup in
   its local mapping table to retrieve individual mappings, instantiated
   by the requesting Control Point (i.e., authorization checks), that
   match the signaled port range (i.e., the external port is within the
   "StartPort" and "EndPort" arguments of DeletePortMappingRange()).  If
   no mapping is found, the "730 PortMappingNotFound" error code is sent
   to the IGD Control Point (Figure 9).  If one or more mappings are
   found, the IGD-PCP IWF generates individual PCP MAP delete requests
   corresponding to these mappings (see the example shown in Figure 10).

   The IGD-PCP IWF MAY send a positive answer to the requesting IGD
   Control Point without waiting to receive all the answers from the PCP
   server.

                                    UPnP-PCP
   UPnP Control                   Interworking
      Point                         Function                 PCP Server
        |                              |                          |
        | (1) DeletePortMappingRange() |                          |
        |       StartPort=8596         |                          |
        |       EndPort  =9000         |                          |
        |       Protocol =UDP          |                          |
        |----------------------------->|                          |
        |                              |                          |
        |       (2) Error:             |                          |
        |   PortMappingNotFound        |                          |
        |<-----------------------------|                          |
        |                              |                          |

         Figure 9: Flow Example: Error Encountered when Processing
                         DeletePortMappingRange()




















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RFC 6970                    UPnP IGD-PCP IWF                   July 2013


   Figure 10 illustrates the exchanges that occur when the IWF receives
   DeletePortMappingRange().  In this example, only two mappings having
   the external port number in the 6000-6050 range are maintained in the
   local table.  The IWF issues two MAP requests to delete these
   mappings.

                                    UPnP-PCP
   UPnP Control                   Interworking
      Point                         Function                 PCP Server
        |                              |                          |
        | (1) DeletePortMappingRange() |                          |
        |     StartPort=6000           |                          |
        |     EndPort  =6050           |                          |
        |     Protocol =UDP            |                          |
        |----------------------------->|                          |
        |                              |                          |
        |                              |   (2a) PCP MAP Request   |
        |                              |       Protocol=UDP       |
        |                              |   internal-ip-address    |
        |                              |      internal-port       |
        |                              |   external-ip-address    |
        |                              |   external-port=6030     |
        |                              |   Requested-lifetime=0   |
        |                              |------------------------->|
        |                              |                          |
        |                              |   (2b) PCP MAP Request   |
        |                              |       Protocol=UDP       |
        |                              |   internal-ip-address    |
        |                              |      internal-port       |
        |                              |   external-ip-address    |
        |                              |   external-port=6045     |
        |                              |   Requested-lifetime=0   |
        |                              |------------------------->|
        |                              |                          |
        |     (3) Positive answer      |                          |
        |<-----------------------------|                          |
        |                              |                          |

              Figure 10: Example of DeletePortMappingRange()

5.9.  Renewing a Mapping

   Because of the incompatibility of mapping lifetimes between a UPnP
   IGD and PCP, the IGD-PCP IWF MUST simulate long and even infinite
   lifetimes.  Indeed, for requests having a requested infinite
   PortMappingLeaseDuration, the IGD-PCP IWF MUST set the Requested
   Lifetime of the corresponding PCP request to 4294967296.  If
   PortMappingLeaseDuration is not infinite, the IGD-PCP IWF MUST set



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   the Requested Lifetime of the corresponding PCP request to the same
   value as PortMappingLeaseDuration.  Furthermore, the IGD-PCP
   Interworking Function MUST maintain an additional timer set to the
   initial requested PortMappingLeaseDuration.  Upon receipt of a
   positive answer from the PCP server, the IGD-PCP IWF relays the
   corresponding UPnP IGD response to the requesting IGD Control Point
   with PortMappingLeaseDuration set to the same value as that of the
   initial request.  Then, the IGD-PCP IWF MUST periodically renew the
   constructed PCP mapping until the expiry of PortMappingLeaseDuration.
   Responses received when renewing the mapping MUST NOT be relayed to
   the IGD Control Point.

   If an error is encountered during mapping renewal, the IGD-PCP
   Interworking Function has no means of informing the IGD Control Point
   of the error.

5.10.  Rapid Recovery

   When the IGD-PCP IWF is co-located with the DHCP server, the state
   maintained by the IGD-PCP IWF MUST be updated using the state in the
   local DHCP server.  Particularly, if an IP address expires or is
   released by an internal host, the IGD-PCP IWF MUST delete all the
   mappings bound to that internal IP address.

   Upon change of the external IP address of the IGD-PCP IWF, the
   IGD-PCP IWF MAY renew the mappings it maintained.  This can be
   achieved only if a full state table is maintained by the IGD-PCP IWF.
   If the port quota is not exceeded in the PCP server, the IGD-PCP IWF
   will receive a new external IP address and port numbers.  The IGD-PCP
   IWF has no means of notifying internal IGD Control Points of the
   change of the external IP address and port numbers.  Stale mappings
   will be maintained by the PCP server until their lifetime expires.

      Note: If an address change occurs, protocols that are sensitive to
      address changes (e.g., TCP) will experience disruption.

   [RFC6887] defines a procedure for the PCP server to notify PCP
   clients of changes related to the mappings it maintains.  When an
   unsolicited ANNOUNCE is received, the IGD-PCP IWF makes one or more
   MAP requests with the PREFER_FAILURE option to re-install its
   mappings.  If the PCP server cannot create the requested mappings
   (signaled with the CANNOT_PROVIDE_EXTERNAL error response), the
   IGD-PCP IWF has no means of notifying internal IGD Control Points of
   any changes of the external IP address and port numbers.







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RFC 6970                    UPnP IGD-PCP IWF                   July 2013


   Unsolicited PCP MAP responses received from a PCP server are handled
   as any normal MAP response.  If a response indicates that the
   external IP address or port has changed, the IGD-PCP IWF has no means
   of notifying the internal IGD Control Point of this change.

   Further analysis of PCP failure scenarios for the IGD-PCP
   Interworking Function are discussed in [PCP-FAILURE].

6.  Security Considerations

   IGD:2 access control requirements and authorization levels SHOULD be
   applied by default [IGD2].  When IGD:2 is used, operation on behalf
   of a third party SHOULD be allowed only if authentication and
   authorization are used [IGD2].  When only IGD:1 is available,
   operation on behalf of a third party SHOULD NOT be allowed.

   This document defines a procedure to create PCP mappings for third-
   party devices belonging to the same subscriber.  The means for
   preventing a malicious user from creating mappings on behalf of a
   third party must be enabled as discussed in Section 13.1 of
   [RFC6887].  In particular, the THIRD_PARTY option MUST NOT be enabled
   unless the network on which the PCP messages are to be sent is fully
   trusted -- for example, access control lists (ACLs) installed on the
   PCP client, the PCP server, and the network between them, so that
   those ACLs allow only communications from a trusted PCP client to the
   PCP server.

   An IGD Control Point that issues AddPortMapping(),
   AddAnyPortMapping(), or GetSpecificPortMappingEntry() requests in a
   shorter time frame will create a lot of mapping entries on the PCP
   server.  The means for avoiding the exhaustion of port resources
   (e.g., port quota, as discussed in Section 17.2 of [RFC6887]) SHOULD
   be enabled.

   The security considerations discussed in [RFC6887] and [Sec_DCP]
   should be taken into account.

7.  Acknowledgments

   The authors would like to thank F. Fontaine, C. Jacquenet, X. Deng,
   G. Montenegro, D. Thaler, R. Tirumaleswar, P. Selkirk, T. Lemon,
   V. Gurbani, and P. Yee for their review and comments.

   F. Dupont contributed to previous versions of this document.  Thanks
   go to him for his thorough reviews and contributions.






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RFC 6970                    UPnP IGD-PCP IWF                   July 2013


8.  References

8.1.  Normative References

   [IGD1]     UPnP Forum, "WANIPConnection:1 Service Template
              Version 1.01", November 2001, <http://upnp.org/specs/
              gw/UPnP-gw-WANIPConnection-v1-Service.pdf>.

   [IGD2]     UPnP Forum, "WANIPConnection:2 Service", September 2010,
              <http://upnp.org/specs/gw/
              UPnP-gw-WANIPConnection-v2-Service.pdf>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6887]  Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)", RFC 6887,
              April 2013.

8.2.  Informative References

   [PCP-DESCR-OPT]
              Boucadair, M., Penno, R., and D. Wing, "PCP Description
              Option", Work in Progress, May 2013.

   [PCP-DHCP-OPT]
              Boucadair, M., Penno, R., and D. Wing, "DHCP Options for
              the Port Control Protocol (PCP)", Work in Progress,
              March 2013.

   [PCP-FAILURE]
              Boucadair, M. and R. Penno, "Analysis of Port Control
              Protocol (PCP) Failure Scenarios", Work in Progress,
              May 2013.

   [PCP-PROXY]
              Boucadair, M., Penno, R., and D. Wing, "Port Control
              Protocol (PCP) Proxy Function", Work in Progress,
              June 2013.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 2011.








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   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee,
              "Dual-Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, August 2011.

   [Sec_DCP]  UPnP Forum, "Device Protection:1 Service", February 2011,
              <http://upnp.org/specs/gw/
              UPnP-gw-DeviceProtection-v1-Service.pdf>.

Authors' Addresses

   Mohamed Boucadair
   France Telecom
   Rennes  35000
   France

   EMail: mohamed.boucadair@orange.com


   Reinaldo Penno
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, California  95134
   USA

   EMail: repenno@cisco.com


   Dan Wing
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, California  95134
   USA

   EMail: dwing@cisco.com

















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