Universal Plug and Play (UPnP) Internet Gateway Device (IGD)-Port Control Protocol (PCP) Interworking Function
draft-ietf-pcp-upnp-igd-interworking-03

Abstract

This document specifies the behavior of the UPnP IGD (Internet Gateway Device)/PCP Interworking Function. An UPnP IGD-PCP Interworking Function (IGD-PCP IWF) is required to be embedded in CP (Customer Premises) routers to allow for transparent NAT control in environments where UPnP IGD is used in the LAN side and PCP in the external side of the CP router.

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].

Status of This Memo

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

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

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

This Internet-Draft will expire on March 16, 2013.

Copyright Notice

Copyright (c) 2012 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
• 2. Acronyms
• 3. Architecture Model
• 4. UPnP IGD-PCP Interworking Function: Overview
• 4.1. UPnP IGD-PCP: State Variables
• 4.2. IGD-PCP: Methods
• 4.3. UPnP IGD-PCP: Errors
• 5. Specification of the IGD-PCP Interworking Function
• 5.1. PCP Server Discovery
• 5.2. Control of the Firewall
• 5.3. NAT Control in LAN Side
• 5.4. Port Mapping Tables
• 5.5. Interworking Function Without NAT in the IGD
• 5.6. NAT Embedded in the IGD
• 5.7. Creating a Mapping
• 5.7.1. AddAnyPortMapping()
• 5.7.2. AddPortMapping()
• 5.8. Listing One or a Set of Mappings
• 5.9. Delete One or a Set of Mappings: DeletePortMapping() or DeletePortMappingRange()
• 5.10. Renewal
• 6. IANA Considerations
• 7. Security Considerations
• 8. Acknowledgments
• 9. References
• 9.1. Normative References
• 9.2. Informative References
• Authors' Addresses

1. Introduction

PCP [I-D.ietf-pcp-base] discusses the implementation of NAT control features that rely upon Carrier Grade NAT devices such as a DS-Lite AFTR [RFC6333] or NAT64 [RFC6146]. Nevertheless, in environments where UPnP IGD is used in the local network, an interworking function between UPnP IGD and PCP is required to be embedded in the IGD (see the example illustrated in Figure 1).

Two configurations are considered:

• No NAT function is embedded in the IGD (Internet Gateway Device). This is required for instance in DS-Lite or NAT64 deployments;
• The IGD embeds a NAT function.

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

Figure 1: Flow Example

The UPnP IGD-PCP Interworking Function (IGD-PCP IWF) maintains a local mapping table that stores all active mappings instructed by internal UPnP 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 Interworking Function from the IGD and relying on a PCP-only mode are out of scope of this document.

Considerations related to co-existence of the UPnP IGD-PCP Interworking Function and PCP Proxy [I-D.ietf-pcp-proxy] are out of scope.

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
           UPnP CP UPnP Control Point

3. Architecture Model

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

• Client refers to a host located in the local network.
• IGD Control Point is a UPnP control point using UPnP to control an IGD (Internet Gateway Device).
• IGD is a router supporting UPnP IGD. It is typically a NAT or a firewall.
• Host represents 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 (a.k.a., Provider NAT) while internal hosts continue to use UPnP. In such scenarios, Figure 3 shows the updated model.

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

Figure 4: Cascaded NAT scenario

To ensure a successful interworking between 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 [I-D.ietf-pcp-base] and a UPnP IGD-PCP Interworking Function are embedded in the IGD. In the rest of the document, IGD-PCP Interworking Function refers the UPnP IGD-PCP Interworking Function, which includes PCP Client functionality.

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

4. UPnP IGD-PCP Interworking Function: Overview

Three tables are provided to specify the correspondence between 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 ones.

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 Interworking Function:

ExternaIPAddress:

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 UPnP CP basis.

PortMappingNumberOfEntries:

Managed locally by the UPnP IGD-PCP Interworking Function.

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 not a value different from 1 is signaled.

PortMappingLeaseDuration:

Requested Mapping Lifetime
In IGD:1 [IGD1] 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 5.10). The behavior in the case of a failing renewal is currently undefined.
IGD:1 doesn't define the behavior in the case of state lost, IGD:2 doesn't require to keep state in stable storage, i.e., to make the state to survive resets/reboots. The UPnP IGD-PCP Interworking Function MUST support IGD:2 behavior.

RemoteHost:

Remote Peer IP Address
Note a domain name is allowed by IGD:2 and has to be resolved into an IP address.

ExternalPort:

External Port Number
Mapped to the suggested PCP external port in MAP messages.

InternalPort:

Internal Port Number
Mapped to PCP internal port field in MAP messages.

PortMappingProtocol:

Transport Protocol
Mapped to PCP protocol field in MAP messages. Note IGD only supports TCP and UDP.

InternalClient:

Internal IP Address
InternalClient can be an IP address or a domain name. Only an IP address scheme is supported in PCP. If a domain name is used Point, it must be resolved to an IP address by the Interworking Function when relying the message to the PCP Server.

PortMappingDescription:

Not supported in base PCP
If the local PCP Client support a PCP Option to convey the description, this option SHOULD be used to relay the mapping description.

SystemUpdateID (only for IGD:2):

Managed locally by the UPnP IGD-PCP Interworking Function

A_ARG_TYPE_PortListing (only for IGD:2):

Managed locally by the UPnP IGD-PCP Interworking Function

4.2. IGD-PCP: Methods

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

GetGenericPortMappingEntry:

This request is not relayed to the PCP Server
IGD-PCP Interworking Function maintains an updated list of active mappings instantiated in the PCP Server by internal hosts. See Section 5.8 for more information.

GetSpecificPortMappingEntry:

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

AddPortMapping:

MAP
Refer to Section 5.7.2.

AddAnyPortMapping (for IGD:2 only):

MAP
No issue is encountered to proxy this request to the PCP Server. Refer to Section 5.7.1 for more details.

DeletePortMapping:

MAP with a requested lifetime set to 0
Refer to Section 5.9.

DeletePortMappingRange (for IGD:2 only):

MAP with a lifetime positioned to 0
Individual requests are issued by the IGD-PCP Interworking Function. Refer to Section 5.9 for more details

GetExternalIPAddress:

MAP OpCode (see Section 10.7 of [I-D.ietf-pcp-base])
This can be achieved by requesting 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.
MUST directly return the value of the corresponding State Variable.

GetListOfPortMappings:

See Section 5.8 for more information
The IGD-PCP Interworking Function maintains an updated list of active mappings as instantiated in the PCP Server. The IGD-PCP Interworking Function handles locally this request.

4.3. UPnP IGD-PCP: Errors

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

   1 UNSUPP_VERSION:  501 "ActionFailed"
      Should not happen.

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

   3 MALFORMED_REQUEST:  501 "ActionFailed"

   4 UNSUPP_OPCODE:  501 "ActionFailed"
      Should not happen.

   5 UNSUPP_OPTION:  501 "ActionFailed"
      Should not happen the exception of PREFER_FAILURE (this
      option is not mandatory to support but AddPortMapping() cannot be
      implemented without it).

   6 MALFORMED_OPTION:  501 "ActionFailed"
      Should not happen.

   7 NETWORK_FAILURE:  Not applicable
      Should not happen after communication was successfully established
      with a PCP Server.  

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

   9 UNSUPP_PROTOCOL:  501 "ActionFailed"
      Should not happen.

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

   11 CANNOT_PROVIDE_EXTERNAL:  718 "ConflictInMappingEntry"
      or 714 "NoSuchEntryInArray"

   12 ADDRESS_MISMATCH:  501 "ActionFailed"
      Should not happen.

   13 EXCESSIVE_REMOTE_PEERS: 501 "ActionFailed"

5. Specification of the IGD-PCP Interworking Function

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

This specification assumes the PCP Server is configured to accept MAP OpCode.

The IGD-PCP Interworking Function handles the "Mapping Nonce" as any PCP Client [I-D.ietf-pcp-base].

Further analysis of PCP failure scenarios for the IGD-PCP Interworking Function are discussed in [I-D.boucadair-pcp-failure].

5.1. PCP Server Discovery

The IGD-PCP Interworking Function implements one of the discovery methods identified in [I-D.ietf-pcp-base] (e.g., DHCP [I-D.ietf-pcp-dhcp]). The IGD-PCP Interworking Function behaves as a PCP Client when communicating with provisioned PCP Server(s).

In order to not impact the delivery of local services requiring the control of the local IGD during any failure event to reach the PCP Server (e.g., no IP address/prefix is assigned to the IGD, IGD-PCP Interworking Function MUST NOT be invoked. Indeed, UPnP machinery is used to control that device and therefore lead to successful operations of internal services.

5.2. Control of the Firewall

In order to configure security policies to be applied to inbound and outbound traffic, UPnP IGD can be used to control a local firewall engine.

No IGD-PCP Interworking Function is therefore required for that purpose.

5.3. NAT Control in LAN Side

Internal UPnP Control Points are not aware of the presence of the IGD-PCP Interworking Function in the IGD.

No modification is required in the UPnP Control Point.

5.4. Port Mapping Tables

IGD-PCP Interworking Function MUST store locally all the mappings instantiated by internal UPnP Control Points in the PCP Server. All mappings SHOULD be stored in a permanent storage.

Upon receipt of a PCP MAP Response from the PCP Server, the IGD-PCP Interworking Function MUST retrieve 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.

5.5. Interworking Function Without NAT in the IGD

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

5.6. NAT Embedded in the IGD

When NAT is embedded in the IGD, the IGD-PCP Interworking Function MUST update the content of received mapping messages with the IP address and/or port number belonging to the external interface of the IGD (i.e., after the NAT1 operation in Figure 4) and not as initially positioned by the UPnP Control Point.

All WANIPConnection messages issued by the UPnP Control Point (resp., PCP Server) are intercepted by the IGD-PCP Interworking Function. Then, the corresponding messages (see Section 4.1, Section 4.2 and Section 4.3) are generated by the IGD-PCP Interworking Function and sent to the provisioned PCP Server (resp., corresponding UPnP Control Point). The content of PCP messages received by the PCP Server reflects the mapping information as enforced in the first NAT. In particular, the internal IP address and/or port number of the requests are replaced with the IP address and port number as assigned by the NAT of the IGD. For the reverse path, PCP response messages are intercepted by the IGD-PCP Interworking Function. The content of the corresponding WANIPConnection messages are updated:

• The internal IP address and/or port number as initially positioned by the UPnP Control Point and stored in the IGD NAT are used to update the corresponding fields in received PCP responses.
• The external IP and port number are not altered by the IGD-PCP Interworking Function.
• The NAT mapping entry in the IGD is updated with the result of 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 be lower or equal to the one assigned by the terminating PCP Server.

Without the involvement of the IGD-PCP Interworking Function, the UPnP CP would retrieve an external IP address and port number having a limited scope and which can not be used to communicate with hosts located beyond NAT2 (i.e., assigned by the IGD and not the ones assigned by NAT2 in Figure 4).

5.7. Creating a Mapping

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

5.7.1. AddAnyPortMapping()

When a UPnP Control Point issues a AddAnyPortMapping(), this request is received by the UPnP Server. The request is then relayed to the IGD-PCP Interworking Function which generates a PCP MAP Request (see Section 4.1 for mapping between WANIPConnection and PCP parameters). Upon receipt of a PCP MAP Response from the PCP Server, an XML mapping is returned to the requesting UPnP Control Point (the content of the messages follows the recommendations listed in Section 5.6 or Section 5.5 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 Interworking Function and sent to the requesting UPnP Control Point. If a short lifetime error is returned (e.g., NETWORK_FAILURE, NO_RESOURCES), the PCP IWF MAY re-send the same request to the PCP Server after 30s. If a negative answer is received, the error is then relayed to the requesting UPnP Control Point.

• Justification: Some applications (e.g., uTorrent, Vuzz, Emule) wait approximately 150s, 90s, 90s, respectively for a response after sending an UPnP request. If a short lifetime error occurs, re-sending the requesting may lead to a positive response from the PCP Server. UPnP Control Points are therefore not aware of short lifetime errors that were recovered quickly.

                         UPnP-PCP
UPnP Control           Interworking
   Point                 Function                    PCP Server
     |                      |                             |
     |(1) AddAnyPortMapping |                             |
     |   ExternalPort=8080  |                             |
     |--------------------->|                             |
     |                      |   (2) PCP MAP Request       |
     |                      |requested external port=8080 |
     |                      |---------------------------->|
     |                      |                             |
     |                      |   (3) PCP MAP Response      |
     |                      | assigned external port=6598 |
     |                      |<----------------------------|
     |(4) AddAnyPortMapping |                             |
     |   ReservedPort=6598  |                             |
     |<---------------------|                             |

Figure 5: Flow example when AddAnyPortMapping() is used

If the IGD-PCP Interworking Function fails to establish a communication with the PCP Server, "501 ActionFailed" error code is to be returned to requesting UPnP CP.

5.7.2. AddPortMapping()

A dedicated option called PREFER_FAILURE is defined in [I-D.ietf-pcp-base] 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 UPnP Control Point.

Upon receipt of AddPortMapping() from an UPnP Control Point, the IGD-PCP Interworking Function MUST generate a PCP MAP Request with all requested mapping information as indicated by the UPnP Control Point if no NAT is embedded in the IGD or updated as specified in Section 5.6. In addition, the IGD-PCP IWF MUST insert a PREFER_FAILURE Option to the generated PCP request.

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. If a short lifetime error is returned, the PCP IWF MAY re-send the same request to the PCP Server after 30s. If a negative answer is received, the IGD-PCP IWF relays a negative message to the UPnP Control Point indicating ConflictInMappingEntry as error code. The UPnP Control Point may re-issue a new request with a new requested external port number. This process is repeated until a positive answer is received or maximum retry is reached.

If the PCP Server is able to honor the requested external port, a positive response is sent to the requesting IGD-PCP IWF. Upon receipt of the response from the PCP Server, the returned mapping MUST be stored by the IGD-PCP Interworking Function in its local mapping table and a positive answer MUST be sent to the requesting UPnP Control Point. This answer terminates this exchange.

If the IGD-PCP Interworking Function fails to establish a communication with the PCP Server, "501 ActionFailed" error code is to be returned to requesting UPnP CP.

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 messages exchange when the requested external port is in use.

                         UPnP-PCP
UPnP Control           Interworking
   Point                 Function                  PCP Server
     |                      |                             |
     | (1) AddPortMapping   |                             |
     |   ExternalPort=8080  |                             |
     |     Protocol=TCP     |                             |
     |--------------------->|                             |
     |                      |   (2) PCP MAP Request       |
     |                      |requested external port=8080 |
     |                      |        protocol=TCP         |
     |                      |       PREFER_FAILURE        |
     |                      |---------------------------->|
     |                      |                             |
     |                      |   (3) PCP MAP Response      |
     |                      | assigned external port=8080 |
     |                      |        protocol=TCP         |
     |                      |<----------------------------|
     | (4) AddPortMapping   |                             |
     |   ExternalPort=8080  |                             |
     |     Protocol=TCP     |                             |
     |<---------------------|                             |

Figure 6: Flow Example (Positive Answer)

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

Figure 7: Flow Example (Negative Answer)

• Note: According to some experiments, some UPnP 1.0 implementations, e.g., uTorrent, simply try the same external port X times (usually 4 times) and then fail if the port is in use; if it finds an external port not being used before X times, it will call AddPortMapping(). Also note that some applications uses GetSpecificPortMapping() to check whether a mapping exists.

5.8. Listing One or a Set of Mappings

In order to list active mappings, an UPnP 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 Interworking Function.

Upon receipt of GetSpecificPortMappingEntry() from a UPnP Control Point, the IGD-PCP IWF MUST check first if the external port number is used by the requesting UPnP Control Point. If the external port is already in use by the requesting UPnP Control Point, the IGD-PCP IWF MUST send back a positive answer. If not, the IGD-PCP IWF MUST relay to the PCP Server a MAP request, with short lifetime (e.g., 60s), including a PREFER_FAILURE Option. 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 UPnP 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 UPnP Control Point indicating NoSuchEntryInArray as error code so that the UPnP control point knows the enquired mapping doesn't exist.

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

A UPnP Control Point requests the deletion of one or a list of mappings by issuing DeletePortMapping() or DeletePortMappingRange(). In IGD:2, we assume the IGD applies the appropriate security policies to grant whether a Control Point has the rights to delete one or a set of mappings. When authorization fails, "606 Action Not Authorized" error code MUST be returned the requesting Control Point.

When DeletePortMapping() or DeletePortMappingRange() is received by the IGD-PCP Interworking Function, 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 UPnP Control Point: "714 NoSuchEntryInArray" for DeletePortMapping() or "730 PortMappingNotFound" for DeletePortMappingRange().

Figure 8 shows an example of UPnP Control Point asking to delete a mapping which 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 taking into account the input arguments as included in DeletePortMapping() if no NAT is enabled in the IGD or the corresponding local IP address and port number as assigned by the local NAT if a NAT is enabled in the IGD. When a positive answer is received from the PCP Server, the IGD-PCP Interworking Function updates its local mapping table (i.e., remove the corresponding entry) and notifies the UPnP Control Point about the result of the removal operation. Once PCP MAP delete request is received by the PCP Server, it proceeds to removing the corresponding entry. A PCP MAP delete response is sent back if the removal of the corresponding entry was successful; if not, a PCP Error is sent back to the IGD-PCP Interworking Function including the corresponding error cause (See Section 4.3).

In case DeletePortMappingRange() is used, the IGD-PCP IWF undertakes a lookup on its local mapping table to retrieve individual mappings instantiated by the requesting Control Point (i.e., authorization checks) and matching the signaled port range (i.e., the external port is within "StartPort" and "EndPort" arguments of DeletePortMappingRange()). If no mapping is found, "730 PortMappingNotFound" error code is sent to the UPnP Control Point (Figure 9). If a set of 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 IWF MAY send a positive answer to the requesting UPnP Control Point without waiting to receive all the answers from the PCP Server. It is unlikely to encounter a problem in the PCP leg because the IWF has verified authorization rights and also the presence of the mapping in the local table.

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

Figure 9: Flow example when an error encountered when processing DeletePortMappingRange()

This example 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   |
     |                            |-------------------------->|
     |                            |                           |
     |                            |    (2c)PCP MAP Request    |
     |                            |       protocol=UDP        |
     |                            |   internal-ip-address     |
     |                            |      internal-port        |
     |                            |   external-ip-address     |
     |                            |   external-port= 6045     |
     |                            |   Requested-lifetime= 0   |
     |                            |-------------------------->|
     |                            |                           |
     |    (2b)Positive answer     |                           |
     |<---------------------------|                           |
     |                            |                           |

Figure 10: Example of DeletePortMappingRange()

5.10. Renewal

Because of the incompatibility of mapping lifetimes between UPnP IGD and PCP, the IGD-PCP Interworking Function MUST simulate long and even infinite lifetimes. Indeed, for requests having a requested infinite PortMappingLeaseDuration, the IGD-PCP Interworking Function MUST set the requested PCP Lifetime of the corresponding PCP request to 4294967296. If PortMappingLeaseDuration is not infinite, the IGD-PCP Interworking Function MUST set the requested PCP 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 Interworking Function relays the corresponding UPnP IGD response to the requesting UPnP CP with PortMappingLeaseDuration set to the same value as the one of the initial request. Then, the IGD-PCP Interworking Function MUST renew periodically the instructed PCP mapping until the expiry of PortMappingLeaseDuration. Responses received when renewing the mapping MUST NOT be relayed to the UPnP CP.

In case an error is encountered during mapping renewal, the IGD-PCP Interworking Function has no means to inform the UPnP CP.

6. IANA Considerations

This document makes no request of IANA.

Note to RFC Editor: this section may be removed on publication as an RFC.

7. Security Considerations

IGD:2 authorization framework SHOULD be used [IGD2]. When only IGD:1 is available, one SHOULD consider to enforce the default security, i.e., operation on the behalf of a third party is not allowed.

This document defines a procedure to instruct PCP mappings for third party devices belonging to the same subscriber. Identification means to avoid a malicious user to instruct mappings on behalf of a third party must be enabled. Such means are already discussed in Section 7.4.4 of [I-D.ietf-pcp-base].

Security considerations elaborated in [I-D.ietf-pcp-base] and [Sec_DCP] should be taken into account.

8. Acknowledgments

Authors would like to thank F. Fontaine, C. Jacquenet, X. Deng, G. Montenegro, D. Thaler and R. Tirumaleswar for their review and comments.

9. References

9.1. Normative References

9.2. Informative References

Authors' Addresses