| PCP Working Group | M. Boucadair |
| Internet-Draft | France Telecom |
| Intended status: Standards Track | R. Penno |
| Expires: June 22, 2013 | D. Wing |
| Cisco | |
| December 19, 2012 |
Universal Plug and Play (UPnP) Internet Gateway Device (IGD)-Port Control Protocol (PCP) Interworking Function
draft-ietf-pcp-upnp-igd-interworking-06
This document specifies the behavior of the UPnP IGD (Internet Gateway Device)/PCP Interworking Function. A 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 on the LAN side and PCP on the external side of the CP router.
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].
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/⁠.
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This Internet-Draft will expire on June 22, 2013.
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.
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:
UPnP-PCP
UPnP Control Interworking
Point Function PCP Server
| | |
| (1) AddPortMapping | |
|--------------------->| |
| | (2) PCP MAP Request |
| |-------------------------->|
| | |
Figure 1: Flow Example
The UPnP IGD-PCP IWF (IGD-PCP IWF) maintains a local mapping table that stores all active mappings constructed 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 IWF 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 a PCP Proxy [I-D.ietf-pcp-proxy] are out of scope.
This document makes use of the following abbreviations:
As a reminder, Figure 2 illustrates the architecture model adopted by UPnP IGD [IGD2]. In Figure 2, the following UPnP terminology is used:
+-------------+
| 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 IGD. 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 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 IWF refers the UPnP IGD-PCP Interworking Function, which includes PCP Client functionality.
Without the involvement of the IGD-PCP IWF, 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).
UPnP IGD-PCP IWF is responsible for generating a well-formed PCP message from a received UPnP IGD message, and vice versa.
Three tables are provided to specify the correspondence between UPnP IGD and PCP:
Note that some enhancements have been integrated in WANIPConnection as documented in [IGD2].
Below are listed only the UPnP IGD state variables applicable to the IGD-PCP IWF:
Both IGD:1 and IGD:2 methods applicable to the UPnP IGD-PCP Interworking Function are listed here.
This section lists PCP errors codes and the corresponding UPnP IGD ones. Error codes specific to IGD:2 are tagged accordingly.
This section covers the scenarios with or without NAT in the IGD.
This specification assumes the PCP Server is configured to accept the MAP OpCode.
The IGD-PCP IWF handles the "Mapping Nonce" as any PCP Client [I-D.ietf-pcp-base].
The IGD-PCP IWF 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).
If no IPv4 address / IPv6 prefix is assigned to the IGD or the IGD is unable to determine 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 been talking to a PCP server), a "501 ActionFailed" error message is returned to requesting UPnP CP in case the IGD-PCP IWF fails to establish communication with that PCP Server.
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 IWF is therefore required for that purpose.
The use of IGD-PCP IWF to control an upstream PCP-controlled firewall is out of scope of this document.
The IGD-PCP IWF MUST store locally all the mappings instantiated by internal UPnP 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 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.
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 PCP messages (and mapped back) according to Section 4.1).
When NAT is embedded in the IGD, the IGD-PCP IWF 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 set by the UPnP Control Point.
All WANIPConnection messages issued by the UPnP Control Point are intercepted by the IGD-PCP IWF. Then, the corresponding messages (see Section 4.1, Section 4.2 and Section 4.3) are generated by the IGD-PCP IWF and sent to the provisioned PCP Server. 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 IWF. The content of the corresponding WANIPConnection messages are updated:
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 to the one assigned by the terminating PCP Server.
Two methods can be used to create a mapping: AddPortMapping() or AddAnyPortMapping().
When a UPnP Control Point issues an AddAnyPortMapping(), 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). Upon receipt of a PCP MAP response from the PCP Server, the corresponding UPnP IGD method is returned to the requesting UPnP Control Point (the content of the messages follows 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 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.
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 when AddAnyPortMapping() is used
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 IWF 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 5.5. In addition, the IGD-PCP IWF MUST insert a PREFER_FAILURE Option in the generated PCP request.
If the requested external port is not available, the PCP server will send a CANNOT_PROVIDE_EXTERNAL error response. If a short lifetime error is returned, the IGD-PCP IWF MAY re-send the same request to the PCP Server after 30 seconds. If a PCP error response is received, the IGD-PCP IWF relays a negative message to the UPnP Control Point with ConflictInMappingEntry as the error code. The UPnP Control Point may re-issue a new request with a new requested external port number. This process is typically repeated by the UPnP 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 a positive answer to the requesting UPnP Control Point. This answer terminates this 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 messages 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)
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)
In order to list active mappings, a 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 IWF.
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.
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 determine 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 to the requesting Control Point.
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 UPnP Control Point: "714 NoSuchEntryInArray" for DeletePortMapping() or "730 PortMappingNotFound" for DeletePortMappingRange().
Figure 8 shows an example of a 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 IWF updates its local mapping table (i.e., removes the corresponding entry) and notifies the UPnP Control Point about 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 is sent back to the IGD-PCP IWF including the corresponding error cause (see Section 4.3).
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) and matching the signaled port range (i.e., the external port is within the "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 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).
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()
Because of the incompatibility of mapping lifetimes between 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 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 UPnP CP with PortMappingLeaseDuration set to the same value as the one of the initial request. Then, the IGD-PCP IWF MUST renew periodically the constructed 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.
When the IWF is co-located with the DHCP server, the state maintained by the IWF MUST be updated using the state of the local DHCP server. Particularly, if an IP address expires or is released by an internal host, the IWF MUST delete all the mappings bound to that internal IP address.
Upon change of the external IP address of the IWF, the IWF MAY renew the mappings it maintained. This can be achieved only if a full state table is maintained by the IWF. If the port quota is not exceeded in the PCP server, the IWF will receive a new external IP address and port numbers. The IWF has no means to notify the change of the external IP address and port to internal UPnP CPs. Stale mappings will be maintained by the PCP Server until their lifetime expires.
[I-D.ietf-pcp-base] defines a procedure for the PCP Server to notify PCP Clients about changes related to the mappings it maintains. When an unsolicited ANNOUNCE is received, the 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 (signalled with the CANNOT_PROVIDE_EXTERNAL error response), the IWF has no means to notify the change of the external IP address and port to internal UPnP CPs.
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 IWF has no means to notify the internal UPnP CP of this change.
Further analysis of PCP failure scenarios for the IGD-PCP Interworking Function are discussed in [I-D.boucadair-pcp-failure].
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an RFC.
The IGD:2 authorization framework SHOULD be used [IGD2]. When only IGD:1 is available, operation on the 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. Means to prevent a malicious user from creating mappings on behalf of a third party must be enabled as discussed in Section 13.1 of [I-D.ietf-pcp-base].
The security considerations discussed in [I-D.ietf-pcp-base] and [Sec_DCP] should be taken into account.
Authors would like to thank F. Fontaine, C. Jacquenet, X. Deng, G. Montenegro, D. Thaler, R. Tirumaleswar, and P. Selkirk for their review and comments.
F. Dupont contributed to previous versions of this document. Thanks to him for his thorough reviews and contribution.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [I-D.ietf-pcp-base] | Wing, D, Cheshire, S, Boucadair, M, Penno, R and P Selkirk, "Port Control Protocol (PCP)", Internet-Draft draft-ietf-pcp-base-29, November 2012. |