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IETF RFC 6970
Last modified on Wednesday, July 24th, 2013
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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/RFC 6970.
Boucadair, et al. Standards Track PAGE 1 
RFC 6970 UPnP IGD-PCP IWF July 2013
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
Boucadair, et al. Standards Track PAGE 2
RFC 6970 UPnP IGD-PCP IWF July 2013
1. Introduction
The Port Control Protocol (PCP) specification [RFC 6887] 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) [RFC 6333] or NAT64 [RFC 6146]. 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 [RFC 2119].
Boucadair, et al. Standards Track PAGE 3
RFC 6970 UPnP IGD-PCP IWF July 2013
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.
Boucadair, et al. Standards Track PAGE 4
RFC 6970 UPnP IGD-PCP IWF July 2013
+-------------+
| 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
[RFC 6887], 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.
Boucadair, et al. Standards Track PAGE 5
RFC 6970 UPnP IGD-PCP IWF July 2013
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).
Boucadair, et al. Standards Track PAGE 6
RFC 6970 UPnP IGD-PCP IWF July 2013
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.
Boucadair, et al. Standards Track PAGE 7
RFC 6970 UPnP IGD-PCP IWF July 2013
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 [RFC 6887] 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"
Boucadair, et al. Standards Track PAGE 8
RFC 6970 UPnP IGD-PCP IWF July 2013
4 UNSUPP_OPCODE: 501 "ActionFailed"
[RFC 6887] 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 [RFC 6887].
5.1. PCP Server Discovery
The IGD-PCP IWF implements one of the discovery methods identified in
[RFC 6887] (e.g., DHCP [PCP-DHCP-OPT]). The IGD-PCP Interworking
Function behaves as a PCP client when communicating with provisioned
PCP server(s).
Boucadair, et al. Standards Track PAGE 9
RFC 6970 UPnP IGD-PCP IWF July 2013
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 [RFC 6887].
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 [RFC 6887]. 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).
Boucadair, et al. Standards Track PAGE 10
RFC 6970 UPnP IGD-PCP IWF July 2013
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.
Boucadair, et al. Standards Track PAGE 11
RFC 6970 UPnP IGD-PCP IWF July 2013
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.
Boucadair, et al. Standards Track PAGE 12
RFC 6970 UPnP IGD-PCP IWF July 2013
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 [RFC 6887] 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.
Boucadair, et al. Standards Track PAGE 13
RFC 6970 UPnP IGD-PCP IWF July 2013
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)
Boucadair, et al. Standards Track PAGE 14
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)
Boucadair, et al. Standards Track PAGE 15
RFC 6970 UPnP IGD-PCP IWF July 2013
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.
Boucadair, et al. Standards Track PAGE 16
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.
Boucadair, et al. Standards Track PAGE 17
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()
Boucadair, et al. Standards Track PAGE 18
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
Boucadair, et al. Standards Track PAGE 19
RFC 6970 UPnP IGD-PCP IWF July 2013
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.
[RFC 6887] 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.
Boucadair, et al. Standards Track PAGE 20
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
[RFC 6887]. 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 [RFC 6887]) SHOULD
be enabled.
The security considerations discussed in [RFC 6887] 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.
Boucadair, et al. Standards Track PAGE 21
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>.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 6887] 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.
[RFC 6146] 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.
Boucadair, et al. Standards Track PAGE 22
RFC 6970 UPnP IGD-PCP IWF July 2013
[RFC 6333] 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
Boucadair, et al. Standards Track PAGE 23
RFC TOTAL SIZE: 50900 bytes
PUBLICATION DATE: Wednesday, July 24th, 2013
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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