PCP working group D. Wing, Ed.
Internet-Draft Cisco
Intended status: Standards Track S. Cheshire
Expires: August 25, 2011 Apple
M. Boucadair
France Telecom
R. Penno
Juniper Networks
F. Dupont
Internet Systems Consortium
February 21, 2011
Port Control Protocol (PCP)
draft-ietf-pcp-base-05
Abstract
Port Control Protocol allows a host to control how incoming IPv6 or
IPv4 packets are translated and forwarded by a network address
translator (NAT) or simple firewall to an IPv6 or IPv4 host, and also
allows a host to optimize its NAT keepalive messages.
Status of this Memo
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This Internet-Draft will expire on August 25, 2011.
Copyright Notice
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Copyright (c) 2011 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Deployment Scenarios . . . . . . . . . . . . . . . . . . . 5
2.2. Supported Transport Protocols . . . . . . . . . . . . . . 5
2.3. Single-homed Customer Premises Network . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Relationship of PCP Server and its NAT . . . . . . . . . . . . 8
5. Common Request and Response Header Format . . . . . . . . . . 9
5.1. Request Header . . . . . . . . . . . . . . . . . . . . . . 9
5.2. Response Header . . . . . . . . . . . . . . . . . . . . . 10
5.3. Options . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.4. Result Codes . . . . . . . . . . . . . . . . . . . . . . . 13
6. General PCP Operation . . . . . . . . . . . . . . . . . . . . 14
6.1. General PCP Client: Generating a Request . . . . . . . . . 14
6.2. General PCP Server: Processing a Request . . . . . . . . . 15
6.3. General PCP Client: Processing a Response . . . . . . . . 16
6.4. Multi-interface Issues . . . . . . . . . . . . . . . . . . 16
6.5. Epoch . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.6. Version negotiation . . . . . . . . . . . . . . . . . . . 17
6.7. General PCP Options . . . . . . . . . . . . . . . . . . . 18
6.7.1. UNPROCESSED . . . . . . . . . . . . . . . . . . . . . 18
7. Introduction to MAP and PEER OpCodes . . . . . . . . . . . . . 19
7.1. For Operating a Server . . . . . . . . . . . . . . . . . . 20
7.2. For Reducing NAT Keepalive Messages . . . . . . . . . . . 21
7.3. For Operating a Symmetric Client/Server . . . . . . . . . 22
8. MAP OpCodes . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.1. OpCode Packet Formats . . . . . . . . . . . . . . . . . . 23
8.2. OpCode-Specific Result Codes . . . . . . . . . . . . . . . 26
8.3. OpCode-Specific Client: Generating a Request . . . . . . . 27
8.4. OpCode-Specific Server: Processing a Request . . . . . . . 28
8.5. OpCode-Specific Client: Processing a Response . . . . . . 29
8.6. Mapping Lifetime and Deletion . . . . . . . . . . . . . . 30
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8.7. Subscriber Renumbering . . . . . . . . . . . . . . . . . . 31
8.8. PCP Options for MAP OpCodes . . . . . . . . . . . . . . . 32
8.8.1. THIRD_PARTY . . . . . . . . . . . . . . . . . . . . . 32
8.8.2. REMOTE_PEER_FILTER . . . . . . . . . . . . . . . . . . 34
8.8.3. PREFER_FAILURE . . . . . . . . . . . . . . . . . . . . 36
8.9. PCP Mapping State Maintenance . . . . . . . . . . . . . . 37
8.9.1. Recreating Mappings . . . . . . . . . . . . . . . . . 37
8.9.2. Maintaining Mappings . . . . . . . . . . . . . . . . . 38
9. PEER OpCodes . . . . . . . . . . . . . . . . . . . . . . . . . 39
9.1. OpCode Packet Formats . . . . . . . . . . . . . . . . . . 39
9.2. OpCode-Specific Result Codes . . . . . . . . . . . . . . . 42
9.3. OpCode-Specific Client: Generating a Request . . . . . . . 43
9.4. OpCode-Specific Server: Processing a Request . . . . . . . 43
9.5. OpCode-Specific Client: Processing a Response . . . . . . 43
10. Deployment Considerations . . . . . . . . . . . . . . . . . . 44
10.1. Maintaining Same External IP Address . . . . . . . . . . . 44
10.2. Ingress Filtering . . . . . . . . . . . . . . . . . . . . 44
11. Deployment Scenarios . . . . . . . . . . . . . . . . . . . . . 45
11.1. Dual Stack-Lite . . . . . . . . . . . . . . . . . . . . . 45
11.1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . 45
11.1.2. Encapsulation Mode . . . . . . . . . . . . . . . . . . 46
11.1.3. Plain IPv6 Mode . . . . . . . . . . . . . . . . . . . 46
11.2. NAT64 . . . . . . . . . . . . . . . . . . . . . . . . . . 46
11.3. NAT44 and NAT444 . . . . . . . . . . . . . . . . . . . . . 46
11.4. IPv6 Simple Firewall . . . . . . . . . . . . . . . . . . . 46
12. Security Considerations . . . . . . . . . . . . . . . . . . . 47
12.1. Denial of Service . . . . . . . . . . . . . . . . . . . . 47
12.2. Ingress Filtering . . . . . . . . . . . . . . . . . . . . 47
12.3. Validating Target Address . . . . . . . . . . . . . . . . 48
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 48
13.1. Port Number . . . . . . . . . . . . . . . . . . . . . . . 48
13.2. OpCodes . . . . . . . . . . . . . . . . . . . . . . . . . 48
13.3. Result Codes . . . . . . . . . . . . . . . . . . . . . . . 48
13.4. Options . . . . . . . . . . . . . . . . . . . . . . . . . 48
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 49
15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 49
15.1. Normative References . . . . . . . . . . . . . . . . . . . 49
15.2. Informative References . . . . . . . . . . . . . . . . . . 50
Appendix A. Changes . . . . . . . . . . . . . . . . . . . . . . . 51
A.1. Changes from draft-ietf-pcp-base-04 to -05 . . . . . . . . 51
A.2. Changes from draft-ietf-pcp-base-03 to -04 . . . . . . . . 52
A.3. Changes from draft-ietf-pcp-base-02 to -03 . . . . . . . . 53
A.4. Changes from draft-ietf-pcp-base-01 to -02 . . . . . . . . 53
A.5. Changes from draft-ietf-pcp-base-00 to -01 . . . . . . . . 54
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 54
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1. Introduction
Port Control Protocol (PCP) provides a mechanism to control how
incoming packets are forwarded by upstream devices such as NAT64,
NAT44, and firewall devices, and a mechanism to reduce application
keepalive traffic. PCP is primarily designed to be implemented in
the context of both Carrier-Grade NATs (CGN) and small NATs (e.g.,
residential NATs). PCP allows hosts to operate server for a long
time (e.g., a webcam) or a short time (e.g., while playing a game or
on a phone call) when behind a NAT device, including when behind a
CGN operated by their Internet service provider.
PCP allows applications to create mappings from an external IP
address and port to an internal IP address and port. If the PCP-
controlled device is a NAT, a mapping is created; if the PCP-
controlled device is a firewall, a mapping is created in the
firewall. These mappings are required for successful inbound
communications destined to machines located behind a NAT.
After creating a mapping for incoming connections, it is necessary to
inform remote computers about the IP address and port for the
incoming connection. This is usually done in an application-specific
manner. For example, a computer game would use a rendezvous server
specific to that game (or specific to that game developer), and a SIP
phone would use a SIP proxy. PCP does not provide this rendezvous
function. The rendezvous function will support IPv4, IPv6, or both.
Depending on that support and the application's support of IPv4 or
IPv6, the PCP client will need an IPv4 or IPv6 mapping or both.
Many NAT-friendly applications send frequent application-level
messages to ensure their session will not be timed out by a NAT.
These are commonly called "NAT keepalive" messages, even though they
are not sent to the NAT itself (rather, they are sent 'through' the
NAT). These applications can reduce the frequency of those NAT
keepalive messages by using PCP to learn (or control) the NAT mapping
lifetime. This helps reduce bandwidth on the subscriber's access
network, traffic to the server, and battery consumption on mobile
devices.
Many NATs and firewalls have included application layer gateways
(ALGs) to create mappings for applications that establish additional
streams or accept incoming connections. ALGs incorporated into NATs
additionally modify the application payload. Industry experience has
shown that these ALGs are detrimental to protocol evolution. PCP
allows an application create its own mappings in NATs and firewalls,
removing the incentive to deploy ALGs in NATs and firewalls.
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2. Scope
2.1. Deployment Scenarios
PCP can be used in various deployment scenarios, including:
o Dual Stack-Lite [I-D.ietf-softwire-dual-stack-lite], and;
o NAT64, both Stateful [I-D.ietf-behave-v6v4-xlate-stateful] and
Stateless [I-D.ietf-behave-v6v4-xlate], and;
o Carrier-Grade NAT [I-D.ietf-behave-lsn-requirements], and;
o Basic NAT [RFC3022], and;
o Network Address and Port Translation (NAPT) [RFC3022], such as
commonly deployed in residential NAT devices, and;
o Layer-2 aware NAT [I-D.miles-behave-l2nat] and Dual-Stack Extra
Lite [I-D.arkko-dual-stack-extra-lite], and;
o IPv6 firewall control [RFC6092].
2.2. Supported Transport Protocols
The PCP OpCodes defined in this document are designed to support
transport protocols that use a 16-bit port number (e.g., TCP, UDP,
SCTP, DCCP). Transport protocols that do not use a port number
(e.g., IPsec ESP), and the ability to use PCP to forward all traffic
to a single default host (often nicknamed "DMZ"), are beyond the
scope of this document.
2.3. Single-homed Customer Premises Network
The PCP machinery assumes a single-homed host model. That is, for a
given IP version, only one default route exists to reach the
Internet. This is important because after a PCP mapping is created
and an inbound packet (e.g., TCP SYN) arrives at the host the
outbound response (e.g., TCP SYNACK) has to go through the same path
so the proper address rewriting takes place on that outbound response
packet. This restriction exists because otherwise there would need
to be one PCP server for each egress, because the host could not
reliably determine which egress path packets would take, so the
client would need to be able to reliably make the same internal/
external mapping in every NAT gateway, which in general is not
possible.
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3. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Internal Host, Target Host:
A host served by a NAT gateway, or protected by a firewall.
Remote Host:
A host with which an Internal Host is communicating.
Target Address, External Address, Remote Peer Address:
The address of an Internal Host served by a NAT gateway (typically
a private address [RFC1918]) or an Internal Host protected by a
firewall.
An External Address is the address of an Internal Host as seen by
other Remote Hosts on the Internet with which the Internal Host is
communicating, after translation by any NAT gateways on the path.
An External Address is generally a public routable (i.e., non-
private) address. In the case of an Internal Host protected by a
pure firewall, with no address translation on the path, its
External Address is the same as its Internal Address.
A Remote Peer Address is the address of a Remote Host, as seen by
the Internal Host. A Remote Address is generally a public
routable address. In the case of a Remote Host that is itself
served by a NAT gateway, the Remote Address my in fact be the
Remote Host's External Address, but since this remote translation
is generally invisible to software running on the Internal Host,
the distinction can safely be ignored for the purposes of this
document.
Third Party:
In the common case, an Internal Host manages its own Mappings
using PCP requests, and the Internal Address of those Mappings is
the same as the source IP address of the PCP request packet.
In the case where one device is managing Mappings on behalf of
some other device which does not implement PCP, the presence of
the THIRD_PARTY option in the MAP request signifies that the
specified address, not the source IP address of the PCP request
packet, should be used as the Internal Address for the Mapping.
When PCP requests are used with the THIRD_PARTY option,
appropriate security measures MUST be used to ensure that the
device creating, renewing, or deleting mappings is authorized to
do so on behalf of the internal address given in the THIRD_PARTY
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option.
Mapping:
A NAT mapping creates a relationship between an internal IP
transport address and an external IP transport address. More
specifically, it creates a translation rule where packets destined
to the external IP and port are translated to the internal IP and
port. In the case of a pure firewall, the "Mapping" is the
identity function, translating an internal port number to the same
external port number and vice versa, and this "Mapping" indicates
to the firewall that traffic to and from this internal port number
is permitted to pass. See also Port Forwarding.
Mapping Types:
There are three different ways to create mappings: implicit
dynamic mappings, explicit dynamic mappings, and static mappings.
Implicit dynamic mappings are created as a result of a TCP SYN or
outgoing UDP packet. Explicit dynamic mappings are created as a
result of PCP MAP requests. Both implicit and explicit dynamic
mappings are dynamic in the sense that they are created on demand,
as requested (implicitly or explicitly) by the Internal Host, and
have a lifetime, after which they are automatically deleted unless
the lifetime is extended by action by the Internal Host. Static
mappings are created by manual configuration (e.g., command
language interface or web page) and differ from dynamic mappings
in that their lifetime is typically infinite (they exist until
manually removed) but otherwise they behave exactly the same as
dynamic mappings. For example, a PCP MAP request to create a
mapping that already exists as a static mapping will return a
successful result, confirming that the requested mapping exists.
Port Forwarding, Port Mapping:
Port forwarding (or port mapping) allows a host to receive traffic
sent to a specific IP address and port.
In the context of a NAT or NAPT, the Internal Address and External
Address are different. In the context of a pure firewall, the
Internal Address and External Address are the same. In both
contexts, if an internal host is listening to connections on a
specific port (that is, operating as a server), the external IP
address and port number need to be port forwarded to the internal
IP address and port number, which may be the same, in the case of
a pure firewall. In the context of a NAPT, it is possible that
both the IP address and port are modified. For example with a
NAPT, a webcam might be listening on port 80 on its internal
address 192.168.1.1, while its publicly-accessible external
address is 192.0.2.1 and port is 12345. The NAT does 'port
forwarding' of one to the other.
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PCP Client:
A PCP software instance responsible for issuing PCP requests to a
PCP server. One or several PCP Clients can be embedded in the
same host. Several PCP Clients can be located in the same local
network of a given subscriber. A PCP Client can issue PCP request
on behalf of a third party device of the same subscriber. An
interworking function, from UPnP IGD to PCP, or from NAT-PMP
[I-D.cheshire-nat-pmp] is another example of a PCP Client. A PCP
server in a NAT gateway that is itself a client of another NAT
gateway (nested NAT) may itself act as a PCP client to the
upstream NAT.
PCP Server:
A network element which receives and processes PCP requests from a
PCP client. See also Section 4.
Interworking Function:
a functional element responsible for interworking another protocol
with PCP. For example interworking between UPnP IGD [IGD] with
PCP or NAT-PMP [I-D.cheshire-nat-pmp] and PCP.
subscriber:
an entity provided access to the network. In the case of a
commercial ISP, this is typically a single home.
host:
a device which can have packets sent to it, as a result of PCP
operations. A host is not necessarily a PCP client.
5-tuple The 5 pieces of information that fully identify a flow:
source IP address, destination IP address, protocol, source port
number, destination port number.
4. Relationship of PCP Server and its NAT
The PCP server receives PCP requests. The PCP server might be
integrated within the NAT or firewall device (as shown in Figure 1)
which is expected to be a common deployment.
+-----------------+
+------------+ | NAT or firewall |
| PCP client |-<network>-+ with +---<Internet>
+------------+ | PCP server |
+-----------------+
Figure 1: NAT or Firewall with Embedded PCP Server
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It is also possible to operate the PCP server in a separate device
from the NAT, so long as such operation is indistinguishable from the
PCP client's perspective.
5. Common Request and Response Header Format
All PCP messages contain a request (or response) header containing an
opcode, any relevant opcode-specific information, and zero or more
options. The packet layout for the common header, and operation of
the PCP client and PCP server are described in the following
sections. The information in this section applies to all OpCodes.
Behavior of the OpCodes defined in this document is described in
Section 8 and Section 9.
5.1. Request Header
All requests have the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Version = 0 |R| OpCode | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Reserved (48 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: (optional) opcode-specific information :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: (optional) PCP Options :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Common Request Packet Format
These fields are described below:
1 A single bit set to 1. This allows DTLS and non-DTLS to be
multiplexed on same port, should a future update to this
specification add DTLS support.
Version: This document specifies protocol version 0. Should later
updates to this document specify different message formats with a
version number greater than zero, the first two bytes of those new
message formats will still contain the version number and opcode
as shown here, so that a PCP server receiving a message format
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newer or older than the version(s) it understands can still parse
enough of the message to correctly identify the version number,
and determine whether the problem is that this server is too old
and needs to be updated to work with the PCP client, or whether
the PCP client is too old and needs to be updated to work with
this server.
R: Indicates Request (0) or Response (1). All Requests MUST use 0.
OpCode: Opcodes are defined in Section 8 and Section 9. New OpCodes
can be defined per rules described in Section 13.
Reserved: 48 reserved bits, MUST be sent as 0 and MUST be ignored
when received.
5.2. Response Header
All responses have the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| Version = 0 |R| OpCode | Reserved | Result Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Epoch |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: (optional) OpCode-specific response data :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: (optional) Options :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Common Response Packet Format
These fields are described below:
1 A single bit set to 1.
Ver: This document specifies protocol version 0. Should later
updates to this document specify different message formats with a
version number greater than zero, the first four bytes of those
new message formats will still contain the version number, opcode,
and result code, as shown here, so that a PCP client receiving a
message format newer or older than the version(s) it understands
can still parse enough of the message to correctly identify the
version number, and determine whether the problem is that this
client is too old and needs to be updated to work with the PCP
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server, or whether the PCP server is too old and needs to be
updated to work with this client.
R: Indicates Request (0) or Response (1). All Responses MUST use 1.
OpCode: The OpCode value, copied from the request.
Reserved: 8 reserved bits, MUST be sent as 0, MUST be ignored when
received. This is set by the server.
Result Code: The result code for this response. See Section 5.4 for
values. This is set by the server.
Epoch: The server's Epoch value. See Section 6.5 for discussion.
This value is set both success and error responses.
5.3. Options
A PCP OpCode can be extended with an Option. Options can be used in
requests and responses. It is anticipated that Options will include
information which are associated with the normal function of an
OpCode. For example, an Option could indicate DSCP [RFC2474]
markings to apply to incoming or outgoing traffic associated with a
PCP mapping, or an Option could include descriptive text (e.g., "for
my webcam").
Options use the following Type-Length-Value format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Code | Reserved | Option-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: (optional) data :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Options Header
The description of the fields is as follows:
Option Code: Option code, 8 bits. The first bit of the option code
is the "P" bit, described below. Option codes MUST be registered
with IANA following the procedure described in Section 13.
Reserved: MUST be set to 0 on transmission and MUST be ignored on
reception.
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Option-Length: Indicates in units of 4 octets the length of the
enclosed data. Options with length of 0 are allowed.
data: Option data. The option data MUST end on a 32 bit boundary,
padded with 0's when necessary.
A given Option MAY be included in a request or a response, as
permitted by that Option. If a given Option was included in a
request, and understood and processed by the PCP server, it MUST be
included in the response. The handling of an Option by the PCP
client and PCP server MUST be specified in an appropriate document
and must include whether the PCP Option can appear (one or more
times) in a request, and indicate the contents of the Option in the
request and in the response. If an Option appears in a request or
response more often than allowed, the first occurence(s) is used and
the others simply ignored as if they were not present. If several
Options are included in a PCP request or response, they can be
encoded in any order by the PCP client and are processed in the order
received. If, while processing an option, an error is encountered
that causes a PCP error response to be generated, the PCP request
causes no state change in the PCP server or the PCP-controlled device
(i.e., it rolls back any changes it might have made while processing
the request). The response MUST encode the Options in the same
order, but may omit some PCP Options in the response, as is necessary
to indicate the PCP server does not understand that Option or simply
because that Option is not included in responses. Additional Options
included in the response (if any) MUST be included at the end. A
certain Option MAY appear more than once in a request or in a
response, if permitted by the definition of the Option itself. If
the Option's definition allows the Option to appear once but it
appears more than once in a request, the PCP server MUST respond with
the MALFORMED_OPTION result code; if this occurs in a response, the
PCP client processes the first occurrence and ignores the other
occurrences.
If the "P" bit in the OpCode is set,
o the PCP server MUST only generate a positive PCP response if it
can successfully process the PCP request and this Option.
o if the PCP server does not implement this Option, or cannot
perform the function indicated by this Option (e.g., due to a
parsing error with the option), it MUST generate a failure
response with code UNSUPP_OPTION or MALFORMED_OPTION (as
appropriate) and include the UNPROCESSED option in the response
(Section 6.7.1).
If the "P" bit is clear, the PCP server MAY process or ignore this
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Option.
To enhance interoperability, newly defined Options should avoid
interdependencies with each other.
New Options MUST include the information below:
This Option:
name: <mnemonic>
number: <value>
purpose:
is valid for OpCodes: <list of OpCodes>
length: <rules for length>
may appear in: <requests/responses/both>
maximum occurrences: <count>
5.4. Result Codes
The following result codes may be returned as a result of any OpCode
received by the PCP server. The only success result code is 0, other
values indicate an error.
0 SUCCESS, success
1 UNSUPP_VERSION, unsupported version.
2 UNSUPP_OPCODE, unsupported OpCode.
3 UNSUPP_OPTION, unsupported Option. This error only occurs if the
Option is in the mandatory-to-process range.
4 MALFORMED_OPTION, malformed Option (e.g., exists too many times,
invalid length).
5 UNSPECIFIED_ERROR, server encountered unspecified error.
6 MALFORMED_REQUEST.
Additional result codes, specific to the OpCodes defined in this
document, are listed in Section 8.2 and Section 9.2 .
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6. General PCP Operation
PCP messages MUST be sent over UDP, and the PCP server MUST listen
for PCP requests on the PCP port number (Section 13.1). Every PCP
request generates a response, so PCP does not need to run over a
reliable transport protocol.
PCP is idempotent, so if the PCP client sends the same request
multiple times and the PCP server processes those requests, the same
result occurs. The order of operation is that a PCP client generates
and sends a request to the PCP server which processes the request and
generates a response back to the PCP client.
6.1. General PCP Client: Generating a Request
This section details operation specific to a PCP client, for any
OpCode. Procedures specific to the MAP OpCodes are described in
Section 8, and procedures specific to the PEER OpCodes are described
in Section 9.
Prior to sending its first PCP message, the PCP client determines
which servers to use. The PCP client performs the following steps to
determine its PCP server(s):
1. if a PCP server is configured (e.g., in a configuration file),
the address(es) of the PCP server(s) used as the list of PCP
server(s), else;
2. if DHCP indicates the PCP server(s), the address(es) of the
indicated PCP server(s) are used as the the list of PCP
server(s), else;
3. the address of the default router is used as the PCP server.
With that list of PCP servers, the PCP client formulates its PCP
request. The PCP request contains a PCP common header, PCP OpCode
and payload, and (possibly) Options. It initializes a retransmission
timer to 4 seconds. (As with all UDP or TCP clients on any operating
system, when several PCP clients are embedded in the same host, each
uses a distinct source port number to disambiguate their requests and
replies.) The PCP client sends a PCP message to each server in
sequence, waiting for a response until its timer expires. Once a PCP
client has successfully communicated with a PCP server, it continues
communicating with that PCP server until that PCP server becomes non-
responsive, which causes the PCP client to attempt to re-iterate the
procedure starting with the first PCP server on its list. If a hard
ICMP error is received the PCP client SHOULD immediately abort trying
to contact that PCP server (see Section 2 of [RFC5461] for discussion
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of ICMP and ICMPv6 hard errors). If no response is received from any
of those servers, it doubles its retransmission timer and tries each
server again. This is repeated 4 times (for a total of 5
transmissions to each server). If, after these transmissions, the
PCP client has still not received a response, the PCP client SHOULD
abort the procedure.
[Ed. Note: We need to define precisely what we mean by "non-
responsive". No response after some number of retransmissions?
How many? No response within what time period? -- SC]
Upon receiving a response (success or error), the PCP client does not
change to a different PCP server. That is, it does not "shop around"
trying to find a PCP server to service its (same) request.
6.2. General PCP Server: Processing a Request
This section details operation specific to a PCP server.
Upon receiving a PCP request message, the PCP server parses and
validates it. A valid request contains a valid PCP common header,
one valid PCP Opcode, and zero or more Options (which the server
might or might not comprehend). If an error is encountered during
processing, the server generates an error response which is sent back
to the PCP client. Processing an OpCode and the Options are specific
to each OpCode.
If the received message is shorter than 4 octets, has the R bit set,
or the first bit is clear, the request is simply dropped. If the
version number is not supported, a response is generated containing
the UNSUPP_VERSION response code and the protocol version which the
server does understand (if the server understands a range of protocol
versions then it returns the supported version closest to the version
in the request).
If the OpCode is not supported, a response is generated with the
UNSUPP_OPCODE response code. If the length of the request exceeds
1024 octets or is not a multiple of 4 octets, it is invalid. Invalid
requests are handled by copying up to 1024 octets of the request into
the response, setting the response code to MALFORMED_REQUEST, and
zero-padding the response to a multiple of 4 octets if necessary.
Error responses have the same packet layout as success responses,
with fields copied from the request copied into the response, and
other fields assigned by the PCP server set to 0.
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[Ed. Note: Need more detail around how an error response is
formed, and what it contains.]
6.3. General PCP Client: Processing a Response
The PCP client receives the response and verifies the source IP
address and port belong to the PCP server of an outstanding request.
It validates the version number and OpCode matches an outstanding
request. Responses shorter than 12 octets, longer than 1024 octets,
or not a multiple of 4 octets are invalid and ignored, likely causing
the request to be re-transmitted. The response is further matched by
comparing fields in the response OpCode-specific data to fields in
the request OpCode-specific data. After a successful match with an
outstanding request, the PCP client checks the Epoch field to
determine if it needs to restore its state to the PCP server (see
Section 6.5).
If the response code is 0, the PCP client knows the request was
successful.
If the response code is not 0, the request failed. If the response
code is UNSUPP_VERSION, processing continues as described in
Section 6.6. The PCP client MAY resend the same message but MUST
first wait until the smaller of 30 minutes or the value of the
Lifetime field. If the PCP client has re-discovered a new PCP server
(e.g., connected to a new network), the PCP client is not restricted
from communicating immediately with its new PCP server.
Non-0 responses will normally have a value in the Assigned Lifetime
field. Clients SHOULD NOT repeat the same request to the same PCP
server within the lifetime given in the error response. In the case
of the SERVER_OVERLOADED error response, clients SHOULD NOT send
*any* further requests to the that PCP server within the lifetime
given in the SERVER_OVERLOADED error response.
6.4. Multi-interface Issues
Hosts which desire a PCP mapping might be multi-interfaced (i.e., own
several logical/physical interfaces). Indeed, a host can be dual-
stack or be configured with several IP addresses. These IP addresses
may have distinct reachability scopes (e.g., if IPv6 they might have
global reachability scope as for GUA (Global Unicast Address) or
limited scope such as ULA (Unique Local Address, [RFC4193])).
IPv6 addresses with global reachability scope SHOULD be used as
internal IP address when requesting a PCP mapping in a PCP-controlled
device. IPv6 addresses with limited scope (e.g., ULA), SHOULD NOT be
indicated as internal IP address in a PCP message.
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As mentioned in Section 2.3, only single-homed CP routers are in
scope. Therefore, there is no viable scenario where a host located
behind a CP router is assigned with two GUA addresses belonging to
the same global IPv6 prefix.
[Ed. Note: text regarding multi-homing needs work.]
6.5. Epoch
Every PCP response sent by the PCP server includes an Epoch field.
This field increments by 1 every second, and indicates to the PCP
client if PCP state needs to be restored. If the PCP server resets
or loses the state of its explicit dynamic Mappings (that is, those
mappings created by PCP MAP requests), due to reboot, power failure,
or any other reason, it MUST reset its Epoch time to 0. Similarly,
if the public IP address(es) of the NAT (controlled by the PCP
server) changes, the Epoch MUST be reset to 0. A PCP server MAY
maintain one Epoch value for all PCP clients, or MAY maintain
distinct Epoch values for each PCP client; this choice is
implementation-dependent.
Whenever a client receives a PCP response, the client computes its
own conservative estimate of the expected Epoch value by taking the
Epoch value in the last packet it received from the gateway and
adding 7/8 (87.5%) of the time elapsed since that packet was
received. If the Epoch value in the newly received packet is less
than the client's conservative estimate by more than one second, then
the client concludes that the PCP server lost state, and the client
MUST immediately renew all its active port mapping leases as
described in Section 8.9.1.
When the PCP server reduces its Epoch value, the PCP clients will
send PCP requests to refresh their mappings. The PCP server needs to
be scaled appropriately to accomodate this traffic. Because PCP
lacks a mechanism to simultaneously inform all PCP clients of the
Epoch value, the PCP clients will not flood the PCP server
simultaneously when the PCP server reduces its Epoch value.
6.6. Version negotiation
A PCP client sends its requests using PCP version number 0. Should
later updates to this document specify different message formats with
a version number greater than zero it is expected that PCP servers
will still support version 0 in addition to the newer version(s).
However, in the event that a server returns a response with error
code UNSUPP_VERSION, the client MAY log an error message to inform
the user that it is too old to work with this server, and the client
SHOULD set a timer to retry its request in 30 minutes (in case this
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was a temorary condition and the server configuration is changed to
rectify the situation).
If future PCP versions greater than zero are specified, version
negotiation is expected to proceed as follows:
1. If a client or server supports more than one version it SHOULD
support a contiguous range of versions -- i.e., a lowest version
and a highest version and all versions in between.
2. Client sends first request using highest (i.e., presumably
'best') version number it supports.
3. If server supports that version it responds normally.
4. If server does not support that version it replies giving a
response containing the error code UNSUPP_VERSION, and the
closest version number it does support (if the server supports a
range of versions higher than the client's requested version, the
server returns the lowest of that supported range; if the server
supports a range of versions lower than the client's requested
version, the server returns the highest of that supported range).
5. If the client receives an UNSUPP_VERSION response containing a
version it does support, it records this fact and proceeds to use
this message version for subsequent communication with this PCP
server (until a possible future UNSUPP_VERSION response if the
server is later updated, at which point the version negotiation
process repeats).
6. If the client receives an UNSUPP_VERSION response containing a
version it does not support then the client MAY log an error
message to inform the user that it is too old to work with this
server, and the client SHOULD set a timer to retry its request in
30 minutes.
6.7. General PCP Options
The following options can appear in certain PCP responses.
6.7.1. UNPROCESSED
If the PCP server cannot process a mandatory-to-process option, for
whatever reason, it includes the UNPROCESSED Option in the response,
shown in Figure 5. This helps with debugging interactions between
the PCP client and PCP server. For simplicity, no more than 4
options can be encoded. This option MUST NOT appear more than once
in a PCP response, no matter how many PCP options appeared in the
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request and were unprocessed by the PCP server. If only one Option
code was unprocessed, that option code it is placed in option-code-1
(and the other three fields are set to zero), if two Option codes
were unprocessed, their option codes are placed in option-code-1 and
option-code-2, and so on. If a certain Option appeared more than
once in the PCP request, that Option value only appears once in the
option-code fields. The order of the Options in the PCP request has
no relationship with the order of the Option values in this
UNPROCESSED Option. This Option MUST NOT appear in a response unless
the associated request contained at least one mandatory-to-process
Option. This Option MUST NOT appear more than once.
The UNPROCESSED option is formatted as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-code-1 | option-code-2 | option-code-3 | option-code-4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-code-5 | option-code-6 | option-code-7 | option-code-8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: UNPROCESSED option
This Option:
name: UNPROCESSED
number: 1
purpose: indicates which PCP options in the request are not
supported by the PCP server
is valid for OpCodes: all
length: 1
may appear in: responses, and only if the response code is non-
zero.
maximum occurrences: 1
7. Introduction to MAP and PEER OpCodes
There are three uses for the MAP and PEER OpCodes defined in this
document: a host operating a server (and wanting an incoming
connection), a host operating a client (and wanting to optimize the
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application keepalive traffic), and a host operating a client and
server on the same port. These are discussed in the following
sections.
When operating a server (Section 7.1 and Section 7.3) the PCP client
knows if it wants an IPv4 listener, IPv6 listener, or both on the
Internet. The PCP client also knows if it has an IPv4 interface on
itself or an IPv6 interface on itself. It takes the union of this
knowledge to decide to send a one or two MAP requests for each of its
interfaces. Applications that embed IP addresses in payloads (e.g.,
FTP, SIP) will find it beneficial to avoid address family
translation, if possible.
7.1. For Operating a Server
A host operating a server (e.g., a web server) listens for traffic on
a port, but the server never initiates traffic from that port. For
this to work across a NAT or a firewall, the application needs to (a)
create a mapping from a public IP address and port to itself as
described in Section 8 and (b) publish that public IP address and
port via some sort of rendezvous server (e.g., DNS, a SIP message, a
proprietary protocol). Publishing the public IP address and port is
out of scope of this specification. To accomplish (a), the
application follows the procedures described in this section.
As normal, the application needs to begin listening to a port, and to
ensure that it can get exclusive use of that port it needs to choose
a port that is not in the operating system's ephemeral port range.
Then, the application constructs a PCP message with the appropriate
MAP OpCode depending on if it is listening on an IPv4 or IPv6
interface and if it wants a public IPv4 or IPv6 address.
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The following pseudo-code shows how PCP can be reliably used to
operate a server:
/* start listening on the local server port */
int s = socket(...);
internal_sockaddr = ...;
bind(s, &internal_sockaddr, ...);
listen(s, ...);
requested_external_sockaddr = 0;
pcp_send_map_request(internal_sockaddr,
requested_external_sockaddr, &assigned_external_sockaddr,
requested_lifetime, &assigned_lifetime);
update_rendezvous_server("Client 12345", assigned_external_sockaddr);
while (1) {
int c = accept(s, ...);
/* ... */
}
Figure 6: Pseudo-code for using PCP to operate a server
7.2. For Reducing NAT Keepalive Messages
[Ed. Note: This section creates a difference between an
implicitly-created mapping, which PCP then tries to query/control
using the PEER OpCode, and a explicitly-created mapping which was
created with a MAP OpCode. This section attempts to address PCP
Issue #9 and PCP Issue #35.]
A host operating a client (e.g., XMPP client, SIP client) sends from
a port but never accepts incoming connections on this port. It wants
to ensure the flow to its server is not terminated (due to
inactivity) by an on-path NAT or firewall. To accomplish this, the
applications uses the procedure described in this section.
Middleboxes such as NATs or firewalls need to see occasional traffic
or will terminate their session state, causing application failures.
To avoid this, many applications routinely generate keepalive traffic
for the primary (or sole) purpose of maintaining state with such
middleboxes. Applications can reduce such application keepalive
traffic by using PCP.
Note: For reasons beyond NAT, an application may find it useful to
perform application-level keepalives, such as to detect a broken
path between the client and server, detect a crashed server, or
detect a powered-down client. These keepalives are not related to
maintaining middlebox state, and PCP cannot do anything useful to
reduce those keepalives.
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To use PCP for this function, the applications first connects to its
server, as normal. Afterwards, it issues a PCP request with the
PEER4 or PEER6 OpCode as described in Section 9. The PEER4 OpCode is
used if the host is using IPv4 for its communication to its peer;
PEER6 if using IPv6. The same 5-tuple as used for the connection to
the server is placed into the PEER4 or PEER6 payload.
The following pseudo-code shows how PCP can be reliably used with a
dynamic socket, for the purposes of reducing application keepalive
messages:
int s = socket(...);
connect(s, &remote_peer, ...);
getsockname(s, &internal_address, ...);
external_address = 0;
pcp_send_peer_request(internal_address,
requested_external_address, &assigned_external_address,
remote_peer, requested_lifetime, &assigned_lifetime);
Figure 7: Pseudo-code using PCP with a dynamic socket
7.3. For Operating a Symmetric Client/Server
[Ed. Note: The PEER4 and PEER6 OpCodes, discussed here, are
intended to resolve PCP Issue #35.]
A host operating a client and server on the same port (e.g.,
Symmetric RTP [RFC4961] or SIP Symmetric Response Routing (rport)
[RFC3581]) first establishes a local listener, (usually) sends the
local and public IP addresses and ports to a rendezvous service
(which is out of scope of this document), and (usually) initiates
outbound connections from that same source address. To accomplish
this, the application uses the procedure described in this section.
An application that is using the same port for outgoing connections
as well as incoming connections MUST first signal its operation of a
server using the PCP MAP OpCode, as described in Section 8, and
receive a positive PCP response before it sends any packets from that
port.
Discussion: Although reversing those steps is tempting (to
eliminate the PCP round trip before a packet can be sent from that
port) and will work if the NAT has endpoint-independent mappings
(EIM) behavior, reversing the steps will fail if the NAT does not
have EIM behavior. With a non-EIM NAT, the implicit mapping
created by an outgoing TCP SYN and the explicit mapping created
using the MAP OpCode will cause different ports to be assigned
(which is not desirable; after all, the application is using the
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same port for outgoing and incoming traffic on purpose) and they
will generally also have different lifetimes. PCP does not
attempt to change or dictate how a NAT creates its mappings
(endpoint independent mapping, or otherwise) so there is no
assurance that an implicit mapping will be EIM or non-EIM. Thus,
it is necessary for applications to first signal its operation of
a server using the PCP MAP OpCode.
The following pseudo-code shows how PCP can be used to operate a
symmetric client and server:
/* start listening on the local server port */
int s = socket(...);
internal_sockaddr = ...;
bind(s, &internal_sockaddr, ...);
listen(s, ...);
requested_external_sockaddr = 0;
pcp_send_map_request(internal_sockaddr,
requested_external_sockaddr, &assigned_external_sockaddr,
requested_lifetime, &assigned_lifetime);
update_rendezvous_server("Client 12345", assigned_external_sockaddr);
send_packet(s, "Hello World");
while (1) {
int c = accept(s, ...);
/* ... */
}
Figure 8: Pseudo-code for using PCP to operate a symmetric client/
server
8. MAP OpCodes
This section defines four OpCodes which control forwarding from a NAT
(or firewall) to an internal host. They are:
MAP4=0: create a mapping between an internal address and external
IPv4 address (e.g., NAT44, NAT64, or firewall)
MAP6=1: create a mapping between an internal address and external
IPv6 address (e.g., NAT46, NAT66, or firewall)
The operation of these OpCodes is described in this section.
8.1. OpCode Packet Formats
The two MAP OpCodes (MAP4, MAP6) share a similar packet layout for
both requests and responses. Because of this similarity, they are
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shown together. For both of the MAP OpCodes, if the assigned
external IP address and assigned external port both match the
request's source IP address and MAP OpCode's internal IP address, the
functionality is purely a firewall; otherwise it pertains to a
network address translator which might also perform firewall
functions.
The following diagram shows the request packet format for MAP4 and
MAP6. This packet format is aligned with the response packet format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol | Reserved (24 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Requested external IP address (32 or 128, depending on OpCode):
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| internal port | requested external port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: MAP OpCode Request Packet Format
These fields are described below:
Protocol: indicates protocol associated with this OpCode. Values
are taken from the IANA protocol registry [proto_numbers]. For
example, this field contains 6 (TCP) if the opcode is intended to
create a TCP mapping. The value 0 means "all protocols"
(supported by the PCP server), which is useful to create mappings
for all protocols with a Basic NAT [RFC3022] or a firewall, and
used to delete mappings for all protocols.
Reserved: 24 reserved bits, MUST be sent as 0 and MUST be ignored
when received.
Requested External IP Address: Requested external IP address. This
is useful for refreshing a mapping, especially after the PCP
server loses state. If the PCP server can fulfill the request, it
will do so. If the PCP client doesn't know the external address,
or doesn't have a preference, it MUST use 0.
Requested lifetime: Requested lifetime of this mapping, in seconds.
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Internal port: Internal port for the mapping. The value 0 means
"all ports", which is useful to create mappings for all protocols
with a Basic NAT [RFC3022] or a firewall, and used to delete
mappings for all ports for a protocol. Using 0 for both this
field and the Protocol field indicates "all ports for all
(supported) protocols".
Requested external port: requested external port for the mapping.
This is useful for refreshing a mapping, especially after the PCP
server loses state. If the PCP server can fulfill the request, it
will do so. If the PCP client doesn't know the external port, or
doesn't have a preference, it uses 0.
The following diagram shows the response packet format for MAP4 and
MAP6 OpCodes:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol | Reserved (24 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Assigned external IP address (32 or 128, depending on OpCode) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Lifetime :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| internal port | assigned external port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: MAP OpCode Response Packet Format
These fields are described below:
Protocol: Copied from the request
Reserved: 24 reserved bits, MUST be sent as 0 and MUST be ignored
when received.
Assigned external IP address: On success responses, this is the
assigned external IPv4 or IPv6 address for the mapping; IPv4 or
IPv6 address is indicated by the OpCode. On error responses, this
MUST be 0.
Lifetime: On a success response, this indicates the lifetime for
this mapping, in seconds. On an error response, this indicates
how long clients should assume they'll get the same error response
from the that PCP server if they repeat the same request.
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Internal port: Internal port for the mapping, copied from request.
Assigned external port: On success responses, this is the assigned
external port for the mapping. IPv4 or IPv6 address is indicated
by the OpCode. If the NAT gateway can allocate the requested
external port it SHOULD do so. This is beneficial for re-
establishing state lost when a NAT gateway fails or loses its
state due to reboot. If the NAT gateway cannot allocate the
requested external port but can allocate some other port, it MUST
do so and return the allocated port in the response. Cases where
a NAT gateway cannot allocate the requested external port include
when the requested external port is prohibited by policy, already
used by the NAT gateway for one of its own services (e.g., port 80
for the NAT gateway's own configuration pages) already allocated
to another explicit mapping (by static manual allocation or by a
prior PCP request by a different Internal Host) or the rare case
where the requested external port was already allocated to an
implicit mapping which cannot be 'promoted' to an explicit mapping
for this Internal Host (a different Internal Host already made a
prior outbound connection for which the NAT gateway happened to
assign the external port requested in this explicit PCP request).
On error responses, this MUST be 0.
8.2. OpCode-Specific Result Codes
In addition to the general PCP result codes (Section 5.4), the
following additional result codes may be returned as a result of the
four MAP OpCodes received by the PCP server. These errors are
considered 'long lifetime' or 'short lifetime', which provides
guidance to PCP server developers for the duration of the Lifetime
value for these errors. It is RECOMMENDED that short lifetime errors
use 30 second lifetime and long lifetime errors use 30 minute
lifetime.
19 SERVER_OVERLOADED, server is processing too many MAP requests from
this client or from other clients, and requests this client delay
sending other requests. This is a long lifetime error.
20 NETWORK_FAILURE, e.g., NAT device has not obtained a DHCP lease so
cannot perform a MAP operation. This is a short lifetime error.
21 NO_RESOURCES, e.g., NAT device cannot create more mappings at this
time. This is a system-wide error, and different from
USER_EX_QUOTA. This is a short lifetime error.
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22 UNSUPP_PROTOCOL, unsupported Protocol. This is a long lifetime
error.
23 NOT_AUTHORIZED, e.g., PCP server supports mapping, but the feature
is disabled for this PCP client, or the PCP client requested a
mapping that cannot be fulfilled by the PCP server's security
policy. This is a long lifetime error.
24 USER_EX_QUOTA, mapping would exceed user's port quota. This is a
short lifetime error.
25 CANNOT_PROVIDE_EXTERNAL_PORT, indicates the port is already in use
or otherwise unavailable (e.g., special port that cannot be
allocated by the server's policy). This error is only returned if
the request included the Option PREFER_FAILURE. This is a short
lifetime error.
26 UNABLE_TO_DELETE_ALL, indicates the PCP server was not able to
delete all mappings. This is a short lifetime error.
Other result codes are defined following the procedure in
Section 13.3.
8.3. OpCode-Specific Client: Generating a Request
This section describes the operation of a PCP client when sending
requests with OpCodes MAP4 and MAP6.
There are certain sentinal values used by the MAP OpCodes:
o lifetime=0, indicates a request to delete the specified mapping.
o target IP address=0, indicates all internal IP addresses
associated with this subscriber. This is valid only if lifetime
is also 0. [[THIRD_PARTY]]
o internal-port=0, indicates all ports. This is valid only if
lifetime is also 0.
The request MAY contain values in the requested-external-ip-address
and requested-external-port fields. This allows the PCP client to
attempt to rebuild the PCP server's state, so that the PCP client
could avoid having to change information maintained at the rendezvous
server. Of course, due to other activity on the network (e.g., by
other users or network renumbering), the PCP server may not be able
to fulfill the request.
An existing mapping can have its lifetime extended by the PCP client.
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To do this, the PCP client sends a new MAP request indicating the
internal IP address and port(s).
The PCP client SHOULD renew the mapping before its expiry time,
otherwise it will be removed by the PCP server (see Section 8.6). In
order to prevent excessive PCP chatter, it is RECOMMENDED to send a
single renewal request packet when a mapping is halfway to expiration
time, then, if no positive response is received, another single
renewal request 3/4 of the way to expiration time, and then another
at 7/8 of the way to expiration time, and so on, subject to the
constraint that renewal requests MUST NOT be sent less than four
seconds apart (a PCP client MUST NOT send an infinite number of ever-
closer-together requests in the last few seconds before a mapping
expires).
8.4. OpCode-Specific Server: Processing a Request
This section describes the operation of a PCP server when processing
a request with the OpCodes MAP4 or MAP6.
If the requested lifetime is 0, it indicates a request to delete the
mapping immediately. If the target-ip-address is 0, it indicates all
IP addresses belonging to this subscriber should have all their
mappings removed [[THIRD_PARTY]]. If internal-port is 0, it means
the delete request is for all ports of the particular protocol. On a
deletion request, the requested external port field is ignored by the
server. PCP MAP requests only control mappings created by MAP
requests. So, if the PCP client attempts to delete a static mapping
(i.e., a mapping created outside of PCP itself), the PCP server
deletes all of the PCP-created mappings but MUST respond with
UNABLE_TO_DELETE_ALL result code, with the other fields encoded as
described above. If the PCP client attempts to delete a mapping that
does not exist, the success response code is returned. If the PCP
client is not authorized to delete this mapping, NOT_AUTHORIZED is
returned. If the deletion request was properly formatted, a positive
response is generated with lifetime of 0 and the server copies the
protocol and internal port number from the request into the response;
this positive response is generated even if there is no mapping
(because the mapping could have been already deleted by a previous
PCP transaction).
If the requested lifetime is not zero, it indicates a request to
create a mapping or extend the lifetime of an existing mapping.
Processing of the lifetime is described in Section 8.6.
If the PCP-controlled device is stateless (that is, it does not
establish any per-flow state, and simply rewrites the address and/or
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port in a purely algorithmic fashion), the PCP server simply returns
an answer indicating the external IP address and port yielded by this
stateless algorithmic translation. This allows the PCP client to
learn its external IP address and port as seen by remote peers.
Examples of stateless translators include stateless NAT64 and 1:1
NAT44, both of which modify addresses but not port numbers.
If an Option with value greater than 128 exists but that option does
not make sense (e.g., the PREFER_FAILURE option is included in a
request with lifetime=0), the request is invalid and generates a
MALFORMED_OPTION error.
By default, a PCP-controlled device MUST NOT create mappings for a
protocol not indicated in the request. For example, if the request
was for a TCP mapping, a UDP mapping MUST NOT be created.
If the THIRD_PARTY option is not present in the request, the source
IP address of the PCP packet is used when creating the mapping. If
the THIRD_PARTY option is present, the PCP server validates the
indicated target IP address belongs to the same subscriber. This
validation depends on the PCP deployment scenario; see Section 12.3
for the validation procedure. If the internal IP address in the PCP
request does not belong to the subscriber, an error response MUST be
generated with result code NOT_AUTHORIZED.
Mapings typically consume state on the PCP-controlled device, and it
is RECOMMENDED that a per-subscriber or per-host limit be enforced by
the PCP server to prevent exhausting the mapping state. If this
limit is exceeded, the response code USER_EX_QUOTA is returned.
If all of the proceeding operations were successful (did not generate
an error response), then the requested mappings are created as
described in the request and a positive response is built. This
positive result contains the same OpCode as the request, but with the
"R" bit set.
As a side-effect of creating a mapping, ICMP messages associated with
the mapping MUST be forwarded (and also translated, if appropriate)
for the duration of the mapping's lifetime. This is done to ensure
that ICMP messages can still be used by hosts, without application
programmers or PCP client implementations needing to signal PCP
separately to create ICMP mappings for those flows.
8.5. OpCode-Specific Client: Processing a Response
This section describes the operation of the PCP client when it
receives a PCP response for the OpCodes MAP4 or MAP6.
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A response is matched with a request by comparing the protocol,
internal IP address, and internal port. Other fields are not
compared, because the PCP server sets those fields.
If a successful response, the PCP client can use the external IP
address and port(s) as desired. Typically the PCP client will
communicate the external IP address and port(s) to another host on
the Internet using an application-specific rendezvous mechanism such
as DNS SRV records.
If the response code is IMPLICIT_MAPPING_EXISTS, it indicates the PCP
client is attempting to use MAP when an implicit dynamic connection
already exists for the same internal host and internal port. This
can occur with certain types of NATs. When this is received, if the
PCP client still wants to establish a mapping, the PCP client MUST
choose a different internal port and send a new PCP request
specifying that port.
On an error response, clients SHOULD NOT repeat the same request to
the same PCP server within the lifetime returned in the response.
8.6. Mapping Lifetime and Deletion
The PCP client requests a certain lifetime, and the PCP server
responds with the assigned lifetime. The PCP server MAY grant a
lifetime smaller or larger than the requested lifetime. The PCP
server SHOULD be configurable for permitted minimum and maximum
lifetime, and the RECOMMENDED values are 120 seconds for the minimum
value and 24 hours for the maximum. It is NOT RECOMMENDED that the
server allow lifetimes exceeding 24 hours, because they will consume
ports even if the internal host is no longer interested in receiving
the traffic or no longer connected to the network.
Once a PCP server has responded positively to a mapping request for a
certain lifetime, the port forwarding is active for the duration of
the lifetime unless the lifetime is reduced by the PCP client (to a
shorter lifetime or to zero) or until the PCP server loses its state
(e.g., crashes). However, if the PCP lifetime has reached zero yet
there is still active inside-to-outside traffic, the PCP server MAY,
if it desires, keep the mapping active until the inside-to-outside
traffic has stopped.
An application that forgets its PCP-assigned mappings (e.g., the
application or OS crashes) will request new PCP mappings. This will
consume port mappings. The application will also likely initiate new
implicit dynamic mappings (e.g., TCP connections) without using PCP,
which will also consume port mappings. If there is a port mapping
quota for the internal host, frequent restarts such as this may
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exhaust the quota. PCP provides no explicit protection against such
port consumption. In such environments, it is RECOMMENDED that
applications use shorter PCP lifetimes to reduce the impact of
consuming the user's port quota. An operating system or framework
that issues a mapping request to "delete all" (protocol=0, port=0,
lifetime=0) on reboot protects itself against this resource
exhaustion by voluntarily relinquishing all of its old mappings
before beginning to request new ones. The PCP server MAY chose to
allocate the same (recently relinquished) mappings when mappings are
re-requested by the booting OS. Some port mapping APIs (such as the
"DNSServiceNATPortMappingCreate" API provided by Apple's Bonjour on
Mac OS X, iOS, Windows, Linux, etc.) automatically monitor for
process exit (including application crashes) and automatically send
port mapping deletion requests if the process that requested them
goes away without explicitly relinquishing them.
In order to reduce unwanted traffic and data corruption, a port that
was mapped using the MAP OpCode SHOULD NOT be assigned to another
internal target, or another subscriber, for 120 seconds (MSL,
[RFC0793]). However, the PCP server MUST allow the same internal
target to re-acquire the same port during that same interval.
When a PCP client first acquires a new IP address, it may want to
remove mappings that may have been instantiated for a previous host.
To do this, the PCP client sends a MAP request with protocol,
external port, internal port, and lifetime set to 0.
8.7. Subscriber Renumbering
The customer premises router might obtain a new IPv4 address or new
IPv6 prefix. This can occur because of a variety of reasons
including a reboot, power outage, DHCP lease expiry, or other action
by the ISP. If this occurs, traffic forwarded to the subscriber
might be delivered to another customer who now has that address.
This affects both implicit dynamic mappings and explicit dynamic
mappings. However, this same problem occurs today when a
subscriber's IP address is re-assigned, without PCP and without an
ISP-operated CGN. The solution is the same as today: the problems
associated with subscriber renumbering are caused by subscriber
renumbering and are eliminated if subscriber renumbering is avoided.
PCP defined in this document does not provide machinery to reduce the
subscriber renumbering problem.
When a new Internal Address is assigned to a host embedding a PCP
client, the NAT (or firewall) controlled by the PCP server will
continue to send traffic to the old IP address. Assuming the PCP
client wants to continue receiving traffic, it needs to install new
mappings for its new IP address. The requested external port field
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will not be fulfilled by the PCP server, in all likelihood, because
it is still being forwarded to the old IP address. Thus, a mapping
is likely to be assigned a new external port number and/or public IP
address. Note that this scenario is not expected to happen routinely
on a regular basis for most hosts, since most hosts renew their DHCP
leases before they expire (or re-request the same address after
reboot) and most DHCP servers honor such requests and grant the host
the same address it was previously using before the reboot.
8.8. PCP Options for MAP OpCodes
8.8.1. THIRD_PARTY
This Option is used when a PCP client wants to control a mapping to
another host. A PCP server will only support this option if sent by
an authorized PCP client. Determining which PCP clients are
authorized to use the THIRD_PARTY option depends on the deployment
scenario. For Dual-Stack Lite deployments, the PCP server only
supports this option if the source IPv4 address is the B4's source IP
address. For other scenarios, the subscriber has only one IPv4
address and this Option serves no purpose (and will only generate
error messages from the server). If a subscriber has more than one
IPv4 address, the ISP MUST determine its own policy for how to
identify the trusted device within the subscriber's home. This might
be, for example, the lowest- or highest-numbered host address for
that user's IPv4 prefix.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Target Internal IP address (32 bits of 128 bits, depending :
: on Option length) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields are described below:
Mapping Internal IP Address: Internal IP address of the mapping. If
the length of this Option is 1, this is a 32-bit IPv4 address. If
the length of this Option is 4, this is a 128-bit IPv6 address.
This Option:
name: THIRD_PARTY
number: 131
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purpose: Indicate the MAP request is for a host other than the
host sending the PCP option.
is valid for OpCodes: MAP4, MAP6
length: 1 if OpCode is MAP4, 4 if OpCode is MAP6
may appear in: request. May appear in response only if it
appeared in the associated request.
maximum occurrences: 1
A PCP server is configured to permit third party mappings or to
restrict third party mappings. If third party mappings are
permitted, any host on the network can create, modify, or destroy
mappings for another host on the network, which is generally
undesirable. If third party mappings are restricted, only a certain
host on the network can perform third party mappings. If a PCP
server is configured to restrict third party mappings, and receives a
PCP MCP request with a Target Address that does not match the source
IP address of that request, it MUST generate a UNAUTH_TARGET
response. A customer premise router SHOULD be configured to restrict
third party mappings.
It is RECOMMENDED that PCP servers embedded into customer premise
equipment be configured to restrict third party mappings. With this
configuration, if a user wants to create a third party mapping, the
user needs to interact out-of-band with their customer premise router
(e.g., using its administrative interface).
It is RECOMMENDED that PCP servers embedded into service provider NAT
and firewall devices be configured to permit third party mapings.
With this confguration, if a user wants to create a third party
mapping, the user needs to interact out-of-band with their customer
premise router (e.g., using its administrative interface). This is
because the service provider's PCP server only allows third party
mappings from the subscriber's customer premise router. To do this,
the PCP server needs certain knowledge about the network's
subscribers. It needs to determine the IP address of the
subscriber's customer premise router and to determine the IP subnet
assigned to the subscriber. This knowledge might be dynamic (e.g.,
database query into the service provider's user database for every
incoming PCP request), might be a table (e.g., subscribers with a
certain IPv4 network prefix all have an IPv4 /24, other IPv4 prefixes
have an IPv4 /32, certain IPv6 prefixes have an have an IPv6 /32, and
so on), or might be very static (e.g., all subscribers have one IPv4
address). In many common deployments, there is only one IPv4 address
assigned to a subscriber, and thus the Target Address will always
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match the source address of the PCP message. If there are multiple
IPv4 or multiple IPv6 addresses assigned to a subscriber, the PCP
server allows the highest-numbered address to perform third party
mappings. Thus, on a network supporting PCP with multiple addresses
assigned to a subscriber, the highest-numbered host SHOULD be the
subscriber's customer premise router. Upon receiving a MAP request
where the Target Address does not match the source IP address of the
request, the PCP server determines if the source IP address of the
request is the subscriber's highest numbered address, following the
procedure above. If not, the PCP server MUST generate an
UNAUTH_SOURCE_ADDRESS error. Then the PCP server determines if the
Target Address belongs to the same subscriber as the source IP
address of the PCP packet, using the procedure described above. If
not, the PCP server MUST generate an UNAUTH_TARGET_ADDRESS error.
8.8.2. REMOTE_PEER_FILTER
This Option indicates packet filtering is desired. The remote peer
port and remote peer IP Address indicate the permitted remote peer's
source IP address and port for packets from the Internet. The remote
peer prefix length indicates the length of the remote peer's IP
address that is significant; this allows a single Option to permit an
entire subnet. After processing this MAP request and generating a
successful response, the PCP-controlled device will simply drop
packets with a source IP address, transport, or port that do not
match the fields.
The REMOTE_PEER_FILTER packet layout is described below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | prefix-length | Remote Peer Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Remote Peer IP address (32 bits if MAP4, :
: 1 28 bits if MAP6) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: REMOTE_PEER_FILTER option layout
These fields are described below:
Reserved: 8 reserved bits, MUST be sent as 0 and MUST be ignored
when received.
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prefix-length: indicates how many bits of the IPv4 or IPv6 address
are relevant for this filter. The value 0 indicates "no filter",
and will remove all previous filters. See below for detail.
Remote Peer Port: the port number of the remote peer. The value 0
indicates "all ports"
Remote Peer IP address: The IP address of the remote peer.
This Option:
name: REMOTE_PEER_FILTER
number: 128
is valid for OpCodes: MAP4, MAP6
is included in responses: MUST, if it appeared in the request
length: 2 if used with MAP4, 5 if used with MAP6
may appear in: requests
maximum occurrences: as many as fit within maximum PCP message
size
Because of interactions with dynamic ports this Option MUST only be
used by a client that is operating a server (that is, using the MAP
OpCode), as this ensures that no other application will be assigned
the same ephemeral port for its outgoing connection. Other use by a
PCP client is NOT RECOMMENDED and will cause some UNSAF NAT traversal
mechanisms [RFC3424] to fail where they would have otherwise
succeeded, breaking other applications running on this same host.
The prefix-length indicates how many bits of the IPv6 address or IPv4
address are used for the filter. For MAP4, a prefix-length of 32
indicates the entire IPv4 address is used. For MAP6, a prefix-length
of 128 indicates the entire IPv6 address is used. For MAP4 the
minimum prefix-length value is 0 and the maximum value is 32. For
MAP6 the minimum prefix-length value is 0 and the maximum value is
128. Values outside those range cause an MALFORMED_OPTION response
code.
If multiple occurrences of REMOTE_PEER_FILTER exist in the same MAP
request, they are processed in the same order received, and they MUST
all be successfully processed or return an error (e.g.,
MALFORMED_OPTION if one of the options was malformed). As with other
PCP errors, returning an error causes no state to be changed in the
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PCP server or in the PCP-controlled device. If an existing mapping
exists (with or without a filter) and the server receives a MAP
request with REMOTE_PEER_FILTER, the filters indicated in the new
request are added to any existing filters. If a MAP request has a
lifetime of 0 and contains the REMOTE_PEER_FILTER option, the error
MALFORMED_OPTION is returned.
To remove all existing filters, the prefix-length 0 is used. There
is no mechanism to remove a specific filter.
To change an existing filter, the PCP client sends a MAP request
containing two REMOTE_PEER_FILTER options, the first option
containing a prefix-length of 0 (to delete all existing filters) and
the second containing the new remote peer's IP address and port.
Other REMOTE_PEER_FILTER options in that PCP request, if any, add
more allowed remote hosts.
The PCP server or the PCP-controlled device is expected to have a
limit on the number of remote peers it can support. This limit might
be as small as one. If a MAP request would exceed this limit, the
entire MAP request is rejected with the result code
EXCESSIVE_REMOTE_PEERS, and the state on the PCP server is unchanged.
If this option appears in a request, the following addition result
code could be returned:
27 EXCESSIVE_REMOTE_PEERS, indicates the PCP server was not able to
create the filters in this request. This result code MUST only be
returned if the MAP request contained the REMOTE_PEER_FILTER
Option. This is a long lifetime error.
8.8.3. PREFER_FAILURE
This option indicates that if the PCP server is unable to allocate
the requested port, then instead of returning an available port that
it *can* allocate, the PCP server should instead allocate no port and
return result code CANNOT_HONOR_EXTERNAL_PORT.
This option is intended solely for use by UPnP IGD interworking
[I-D.bpw-pcp-upnp-igd-interworking], where the semantics of IGD
version 1 do not provide any way to indicate to an IGD client that
any port is available other than the one it requested. A PCP server
MAY support this option, if its designers wish to support downstream
devices that perform IGD interworking. PCP servers MAY choose to
rate-limit their handling of PREFER_FAILURE requests, to protect
themselves from a rapid flurry of 65535 consecutive PREFER_FAILURE
requests from clients probing to discover which external ports are
available. PCP servers that are not intended to support downstream
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devices that perform IGD interworking are not required to support
this option. PCP clients other than IGD interworking clients SHOULD
NOT use this option because it results in inefficient operation, and
they cannot safely assume that all PCP servers will implement it.
The option is provided only because the semantics of IGD version 1
offer no viable alternative way to implement an IGD interworking
function. It is anticipated that this option will be deprecated in
the future as more clients adopt PCP natively and the need for IGD
interworking declines.
This Option:
name: PREFER_FAILURE
number: 130
is valid for OpCodes: MAP4, MAP6
is included in responses: MUST
length: 0
may appear in: requests
maximum occurrences: no
8.9. PCP Mapping State Maintenance
If an event occurs that causes the PCP server to lose state (such as
a crash or power outage), the mappings created by PCP are lost. Such
loss of state is rare in a service provider environment (due to
redundant power, disk drives for storage, etc.). But such loss of
state is more common in a residential NAT device which does not write
information to its non-volatile memory.
The Epoch allows a client to deduce when a PCP server may have lost
its state. If this occurs, the PCP client can attempt to recreate
the mappings following the procedures described in this section.
8.9.1. Recreating Mappings
The PCP server SHOULD store mappings in persistent storage so when it
is powered off or rebooted, it remembers the port mapping state of
the network. Due to the physical architecture of some PCP servers,
this is not always achievable (e.g., some non-volatile memory can
withstand only a certain number of writes, so writing PCP mappings to
such memory is generally avoided).
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However, maintaining this state is not essential for correct
operation. When the PCP server loses state and begins processing new
PCP messages, its Epoch is reset to zero (per the procedure of
Section 6.5).
A mapping renewal packet is formatted identically to an original
mapping request; from the point of view of the client it is a renewal
of an existing mapping, but from the point of view of the PCP server
it appears as a new mapping request.
As the result of receiving a packet where the Epoch field indicates
that a reboot or similar loss of state has occurred, the client
renews its port mappings.
The discussion in this section focuses on recreating inbound port
mappings after loss of PCP server state, because that is the more
serious problem. Losing port mappings for outgoing connections
destroys those currently active connections, but does not prevent
clients from establishing new outgoing connections. In contrast,
losing inbound port mappings not only destroys all existing inbound
connections, but also prevents the reception of any new inbound
connections until the port mapping is recreated. Accordingly, we
consider recovery of inbound port mappings the more important
priority. However, clients that want outgoing connections to survive
a NAT gateway reboot can also achieve that using PCP. After
initiating an outbound TCP connection (which will cause the NAT
gateway to establish an implicit port mapping) the client should send
the NAT gateway a port mapping request for the source port of its TCP
connection, which will cause the NAT gateway to send a response
giving the external port it allocated for that mapping. The client
can then store this information, and use it later to recreate the
mapping if it determines that the NAT gateway has lost its mapping
state.
8.9.2. Maintaining Mappings
A PCP client can refresh a mapping by sending a new PCP request
containing information from the earlier PCP response. The PCP server
will respond indicating the new lifetime. It is possible, due to
failure of the PCP server, that the public IP address and/or public
port, or the PCP server itself, has changed (due to a new route to a
different PCP server). To detect such events more quickly, the PCP
client may find it beneficial to use shorter lifetimes (so that it
communicates with the PCP server more often). If the PCP client has
several mappings, the Epoch value only needs to be retrieved for one
of them to verify the PCP server has not lost port forwarding state.
If the client wishes to check the PCP server's Epoch, it sends a PCP
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request for any one of the client's mappings. This will return the
current Epoch value. In that request the PCP client could extend the
mapping lifetime (by asking for more time) or maintain the current
lifetime (by asking for the same number of seconds that it knows are
remaining of the lifetime).
9. PEER OpCodes
This section defines two OpCodes for controlling dynamic connections.
They are:
PEER4=2: Set or query lifetime for flow from IPv4 address to a
remote peer's IPv4 address.
PEER6=3: Set or query lifetime for flow from IPv6 address to a
remote peer's IPv6 address.
The operation of these OpCodes is described in this section.
9.1. OpCode Packet Formats
The two PEER OpCodes (PEER4 and PEER6) share a similar packet layout
for both requests and responses. Because of this similarity, they
are shown together. For both of the PEER OpCodes, if the internal IP
address and internal port fields of the request both match the
external IP address and external port fields of the response, the IP
addresses and ports are not changed and thus the functionality is
purely a firewall; otherwise it pertains to a network address
translator which might also perform firewall functions.
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The following diagram shows the request packet format for PEER4 and
PEER6. This packet format is aligned with the response packet
format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol | Reserved (24 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Internal IP address (32 bits if PEER4, 128 bits if PEER6) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Remote Peer IP address (32 bits if PEER4, 128 bits if PEER6) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Reserved (128 bits) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Requested lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| internal port | reserved (16 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| remote peer port | reserved (16 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: PEER OpCode Request Packet Format
These fields are described below:
Protocol: indicates protocol associated with this OpCode. Values
are taken from the IANA protocol registry [proto_numbers]. For
example, this field contains 6 (TCP) if the OpCode is describing a
TCP peer.
Reserved: 24 reserved bits, MUST be 0 on transmission and MUST be
ignored on reception.
Mapping Internal IP Address: Internal IP address of the 5-tuple.
This can be 32 bits long (if OpCode is PEER4) or 128 bits long (if
OpCode is PEER6).
Remote Peer IP Address: Remote peer's IP address, from the
perspective of the PCP client.
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Reserved: 128 reserved bits, MUST be 0 on transmission and MUST be
ignored on reception.
Requested lifetime: Requested lifetime of this mapping, in seconds.
Unlike the MAP OpCode, there is no special meaning of 0.
internal port: Internal port for the of the 5-tuple.
Reserved: 16 reserved bits, MUST be 0 on transmission and MUST be
ignored on reception.
Remote Peer Port: Remote peer's port of the 5-tuple.
Reserved: 16 reserved bits, MUST be 0 on transmission and MUST be
ignored on reception.
The following diagram shows the response packet format for PEER4 and
PEER6:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol | External_AF | Reserved (16 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Internal IP address (32 bits if PEER4, 128 bits if PEER6) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Remote Peer IP address (32 bits if PEER4, 128 bits if PEER6) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: External IP address (always 128 bits) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Assigned Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| internal port | external port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| remote peer port | reserved (16 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: PEER OpCode Response Packet Format
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Protocol: Copied from the request.
External_AF For success responses, this contains the address family
of the external IP address associated with this peer connection.
Values are from IANA's address family numbers (IPv4 is 1, IPv6 is
2). For error responses, the value MUST be 0.
Reserved: 16 reserved bits, MUST be 0 on transmission, MUST be
ignored on reception.
Internal IP address Copied from the request.
remote Peer IP address Copied from the request.
External IP Address For success responses, this contains the
external IP address, assigned by the NAT (or firewall) to this
mapping. If firewall, this will match the internal IP address.
This field is always 128 bits long. If External_AF indicates
IPv4, the IPv4 address is encoded in the first 32 bits of the
External IP Address field and the remaining 96 bits are zero. For
error responses, this MUST be 0.
Assigned Lifetime: For success responses, this is the assigned
lifetime, in seconds. For error responses, this is 0.s
internal port: copied from request.
external port: For success responses, this is the external port
number, assigned by the NAT (or firewall) to this mapping. If
firewall or 1:1 NAT, this will match the internal port. For error
responses, this MUST be 0.
remote peer port: Copied from request.
Reserved: 16 reserved bits, MUST be 0 on transmission, MUST be
ignored on reception.
9.2. OpCode-Specific Result Codes
In addition to the general PCP result codes (Section 5.4) the
following additional result codes may be returned as a result of the
two PEER OpCodes received by the PCP server.
50 NONEXIST_PEER, the connection to that peer does not exist in the
mapping table
Other result codes are defined following the procedure in
Section 13.3.
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9.3. OpCode-Specific Client: Generating a Request
This section describes the operation of a client when generating the
OpCodes PEER4 or PEER6.
The PEER4 or PEER6 OpCodes MUST NOT be sent until establishing bi-
directional communicaion with the remote peer; for TCP, this means
completing the TCP 3-way handshake.
9.4. OpCode-Specific Server: Processing a Request
This section describes the operation of a server when receiving a
request with the OpCodes PEER4 or PEER6.
The PEER OpCodes provide a single function: the ability for the PCP
client to query and (possibly) extend the lifetime of an existing
mapping.
On receiving the PEER4 or PEER6 OpCode, the PCP server examines the
mapping table. If a mapping does not exist, the NONEXIST_PEER error
is returned.
If the PCP-controlled device can have its lifetime adjusted, the PCP
server uses the smaller of its configured maximum lifetime value and
the requested lifetime from the PEER request, and sets the lifetime
to that value.
Note: The PEER4 or PEER6 OpCodes can never reduce the lifetime of an
existing mapping, nor can those OpCodes delete a mapping. If the
mapping is terminated by the TCP client or server (e.g., TCP FIN or
TCP RST), the mapping will eventually be destroyed normally; the
earlier use of PEER does not extend the lifetime in that case.
If all of the proceeding operations were successful (did not generate
an error response), then a SUCCESS response is generated, with the
assigned-lifetime containing the lifetime of the mapping.
9.5. OpCode-Specific Client: Processing a Response
This section describes the operation of a client when processing a
response with the OpCodes PEER4 or PEER6.
A response is matched with a request by comparing the protocol,
external AF, internal IP address, internal port, remote peer address
and remote peer port. Other fields are not compared, because the PCP
server changes those fields to provide information about the mapping
created by the OpCode.
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If a successful response, the PCP client uses the assigned lifetime
value to reduce its frequency of application keepalives for that
particular NAT mapping. Of course, there may be other reasons,
specific to the application, to use more frequent application
keepalives. For example, the PCP assigned-lifetime could be one hour
but the application may want to ensure the server is still accessible
(e.g., has not crashed) more frequently than once an hour.
If the error response NONEXIST_PEER, this could have occurred if the
PCP client sent its PEER request before the PCP-controlled device had
installed the mapping, or because the mapping has been destroyed
(e.g., due to a TCP FIN). If the PCP client believes the mapping
should exist, the PCP client SHOULD retry the request after a brief
delay (e.g., 5 seconds).
Other error responses SHOULD NOT be retried.
10. Deployment Considerations
10.1. Maintaining Same External IP Address
It is REQUIRED that the PCP-controlled device assign the same
external IP address PCP-created explicit dynamic mappings and to
implicit dynamic mappings. It is RECOMMENDED that static mappings
(e.g., those created by a command language interface on the PCP
server or PCP-controlled device) also be assigned to the same IP
address.
Once all internal hosts belonging to a given subscriber have no
implicit dynamic mappings and have no explicit dynamic mappings in
the PCP-controlled device, a subsequent PCP request for that internal
host MAY be assigned to a different external IP address. Generally,
this re-assignment would occur when a CGN device is load balancing
newly-seen hosts to its public IPv4 address pool.
10.2. Ingress Filtering
To prevent spoofing of PCP requests, ingress filtering [RFC2827] MUST
be performed by devices between the PCP clients and PCP server. For
example, with a PCP server integrated into a customer premise router,
the ethernet switch needs to perform ingress filtering. As another
example, with a PCP server deployed by a service provider, the
service provider's aggregation router (the first device connecting to
subscribers) needs to do ingress filtering.
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11. Deployment Scenarios
11.1. Dual Stack-Lite
The interesting components in a Dual-Stack Lite deployment are the B4
element (which is the customer premises router) and the AFTR element
(which is the device that both terminates the IPv6-over-IPv4 tunnel
and also implements the Carrier-Grade NAT44 function). The B4
element does not need to perform a NAT function (and usually does not
perform a NAT function), but it does operate its own DHCP server and
is the local network's default router.
11.1.1. Overview
Various PCP deployment scenarios can be considered to control the PCP
server embedded in the AFTR element:
1. UPnP IGD and NAT-PMP [I-D.cheshire-nat-pmp] are used in the LAN:
an interworking function is required to be embedded in the B4
element to ensure interworking between the protocol used in the
LAN and PCP. UPnP IGD-PCP Interworking Function is described in
[I-D.bpw-pcp-upnp-igd-interworking].
2. Hosts behind the B4 element will either include a PCP client or
UPnP IGD client, or both.
A. if a UPnP IGD client, the B4 element will need to include an
interworking function from UPnP IGD to PCP.
B. if a PCP client, the PCP client will communicate directly
with the PCP server.
3. The B4 element includes a PCP client which is invoked by an HTTP-
based configuration (as is common today). The internal IP
address field in the PCP payload would be the internal host used
in the port forwarding configuration.
Two modes are identified to forward PCP packets to a PCP server
controlling the provisioned AFTR as described in the following sub-
sections.
[Ed. Note: We need to decide on Encapsulation Mode or Plain IPv6
Mode. This is tracked as PCP Issue #13 [PCP-Issues].]
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11.1.2. Encapsulation Mode
In this mode, B4 element does no processing at all of the PCP
messages, and forwards them as any other UDP traffic. With DS-Lite,
this means that IPv4 PCP messages issued by internal PCP clients are
encapsulated into the IPv6 tunnel sent to the AFTR as for any other
IPv4 packets. The IPv6 address used as source address MUST be the
same as the one used by the B4 element. The AFTR decapsulates the
IPv4 packets and processes the PCP requests (because the destination
IPv4 address points to the PCP server embedded in the AFTR).
11.1.3. Plain IPv6 Mode
Another alternative for deployment of PCP in a DS-Lite context is to
rely on a PCP Proxy in the B4 element. Protocol exchanges between
the PCP Proxy and the PCP server are conveyed using plain IPv6 (no
tunnelling is used). Nevertheless, the IPv6 address used as source
address by the PCP Proxy MUST be the same as the one used by the B4
element.
11.2. NAT64
Hosts behind a NAT64 device can make use of PCP in order to perform
port reservation (to get a publicly routable IPv4 port).
11.3. NAT44 and NAT444
Residential subscribers in NAT44 (and NAT444) deployments are usually
given one IPv4 address, but may also be given several IPv4 addresses.
These addresses are not routable on the IPv4 Internet, but are
routable between the subscriber's home and the ISP's CGN. To
accommodate multiple hosts within a home, especially when provided
insufficient IPv4 addresses for the number of devices in the home,
subscribers operate a NAPT device. When this occurs in conjunction
with an upstream NAT44, this is nicknamed "NAT444".
11.4. IPv6 Simple Firewall
Many IPv6 deployments will include a simple firewall [RFC6092], which
permits outgoing packets to initiate bi-directional communication but
blocks unsolicited incoming packets, which is similar to PCP's
security model that allows a host to create a mapping to itself. In
many situations, especially residential networks that lack an IT
staff, the security provided by an IPv6 simple firewall and the
security provided by PCP are compatible. In such situations, the
IPv6 simple firewall and the IPv6 host can use PCP's OpCode PIN6 to
allow unsolicited incoming packets, so the host can operate a server.
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12. Security Considerations
The PCP client's source port SHOULD be randomly generated [RFC6056].
The PCP server MUST only listen for requests from its internal
interfaces, and MUST NOT listen for requests on its Internet-facing
interfaces.
This document defines Port Control Protocol and two types of OpCodes,
PEER and MAP. The PEER OpCode allows querying and extending (if
permitted) the lifetime of an existing implicit dynamic mapping, so a
host can reduce its keepalive messages. The MAP OpCode allows
creating a mapping so a host can receive incoming unsolicited
connections from the Internet in order to run a server.
The PEER OpCode does not introduce any new security considerations.
On today's Internet, ISPs do not typically filter incoming traffic
for their subscribers. However, when an ISP introduces stateful
address sharing with a NAPT device, such filtering will occur as a
side effect. Filtering will also occur with IPv6 CPE
[I-D.ietf-v6ops-cpe-simple-security]. The MAP OpCode allows a PCP
client to create a mapping so that a host can receive inbound traffic
and operate a server. Security considerations for the MAP OpCode are
described in the following sections.
12.1. Denial of Service
Because the state created in a NAPT or firewall, a per-subscriber
quota will likely exist for both implicit dynamic mappings (e.g.,
outgoing TCP connections) and explicit dynamic mappings (PCP). A
subscriber might make an excessive number of implicit or explicit
dynamic mappings, consuming an inordinate number of ports, causing a
denial of service to other subscribers. Thus, section XXX recommends
that subscribers be limited to a reasonable number of explicit
dynamic mappings.
12.2. Ingress Filtering
It is important to prevent a subscriber from creating a mapping for
another subscriber, because this allows incoming packets from the
Internet and consumes the other user's mapping quota. Both implicit
dynamic mappings (e.g., outgoing TCP connections) and explicit
dynamic mappings (PCP) need ingress filtering. Thus, PCP does not
create a new requirement for ingress filtering.
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12.3. Validating Target Address
The MAP OpCode / THIRD_PARTY contains a Target Address field, which
allows a PCP client to create an explicit dynamic mapping for another
host. Hosts within a subscriber's network cannot create, modify, or
delete mappings of other hosts, except by using the administrative
interface of the customer premise router Section 8.8.1.
13. IANA Considerations
IANA is requested to perform the following actions:
13.1. Port Number
IANA has assigned UDP port 44323 for PCP.
13.2. OpCodes
IANA shall create a new protocol registry for PCP OpCodes, initially
populated with the values in Section 8 and Section 9.
New OpCodes in the range 1-95 can be created via Standards Action
[RFC5226], and the range 96-128 is for Private Use [RFC5226].
13.3. Result Codes
IANA shall create a new registry for PCP result codes, numbered
0-255, initially populated with the result codes from Section 5.4,
Section 8.2, Section 8.8.2, and Section 9.2.
Additional Result Codes can be defined via Specification Required
[RFC5226].
13.4. Options
IANA shall create a new registry for PCP Options, numbered 0-255 with
an associated mnemonic. The values 0-127 are optional-to-process,
and 128-255 are mandatory-to-process. The initial registry contains
the options described in Section 8.8, and the option values 0 and 255
are reserved.
New PCP option codes in the range 0-63 and 128-192 can be created via
Standards Action [RFC5226], and the range 64-127 and 192-255 is for
Private Use [RFC5226].
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14. Acknowledgments
Thanks to Alain Durand, Christian Jacquenet, and Simon Perreault for
their comments and review. Thanks to Simon Perreault for
highlighting the interaction of dynamic connections with PCP-created
mappings.
15. References
15.1. Normative References
[I-D.ietf-behave-v6v4-xlate]
Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", draft-ietf-behave-v6v4-xlate-23 (work in
progress), September 2010.
[I-D.ietf-behave-v6v4-xlate-stateful]
Bagnulo, M., Matthews, P., and I. Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers",
draft-ietf-behave-v6v4-xlate-stateful-12 (work in
progress), July 2010.
[I-D.ietf-softwire-dual-stack-lite]
Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", draft-ietf-softwire-dual-stack-lite-06 (work
in progress), August 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC6056] Larsen, M. and F. Gont, "Recommendations for Transport-
Protocol Port Randomization", BCP 156, RFC 6056,
January 2011.
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[proto_numbers]
IANA, "Protocol Numbers", 2010, <http://www.iana.org/
assignments/protocol-numbers/protocol-numbers.xml>.
15.2. Informative References
[]
Arkko, J., Eggert, L., and M. Townsley, "Scalable
Operation of Address Translators with Per-Interface
Bindings", draft-arkko-dual-stack-extra-lite-05 (work in
progress), February 2011.
[I-D.bpw-pcp-upnp-igd-interworking]
Boucadair, M., Penno, R., Wing, D., and F. Dupont,
"Universal Plug and Play (UPnP) Internet Gateway Device
(IGD)-Port Control Protocol (PCP) Interworking Function",
draft-bpw-pcp-upnp-igd-interworking-02 (work in progress),
February 2011.
[I-D.cheshire-nat-pmp]
Cheshire, S., "NAT Port Mapping Protocol (NAT-PMP)",
draft-cheshire-nat-pmp-03 (work in progress), April 2008.
[I-D.ietf-behave-lsn-requirements]
Yamagata, I., Miyakawa, S., Nakagawa, A., and H. Ashida,
"Common requirements for IP address sharing schemes",
draft-ietf-behave-lsn-requirements-00 (work in progress),
October 2010.
[I-D.ietf-v6ops-cpe-simple-security]
Woodyatt, J., "Recommended Simple Security Capabilities in
Customer Premises Equipment for Providing Residential IPv6
Internet Service", draft-ietf-v6ops-cpe-simple-security-16
(work in progress), October 2010.
[I-D.miles-behave-l2nat]
Miles, D. and M. Townsley, "Layer2-Aware NAT",
draft-miles-behave-l2nat-00 (work in progress),
March 2009.
[IGD] UPnP Gateway Committee, "WANIPConnection:1",
November 2001, <http://upnp.org/specs/gw/
UPnP-gw-WANIPConnection-v1-Service.pdf>.
[PCP-Issues]
PCP Working Group, "PCP Active Tickets", January 2011,
<http://trac.tools.ietf.org/wg/pcp/trac/report/1>.
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[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
December 1998.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022,
January 2001.
[RFC3424] Daigle, L. and IAB, "IAB Considerations for UNilateral
Self-Address Fixing (UNSAF) Across Network Address
Translation", RFC 3424, November 2002.
[RFC3581] Rosenberg, J. and H. Schulzrinne, "An Extension to the
Session Initiation Protocol (SIP) for Symmetric Response
Routing", RFC 3581, August 2003.
[RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)",
BCP 131, RFC 4961, July 2007.
[RFC5461] Gont, F., "TCP's Reaction to Soft Errors", RFC 5461,
February 2009.
[RFC6092] Woodyatt, J., "Recommended Simple Security Capabilities in
Customer Premises Equipment (CPE) for Providing
Residential IPv6 Internet Service", RFC 6092,
January 2011.
Appendix A. Changes
A.1. Changes from draft-ietf-pcp-base-04 to -05
o tweaked PCP common header packet layout.
o Re-added port=0 (all ports).
o minimum size is 12 octets (missed that change in -04).
o removed Lifetime from PCP common header.
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o for MAP error responses, the lifetime indicates how long the
server wants the client to avoid retrying the request.
o More clearly indicated which fields are filled by the server on
success responses and error responses.
A.2. Changes from draft-ietf-pcp-base-03 to -04
o "Pinhole" and "PIN" changed to "mapping" and "MAP".
o Reduced from four MAP OpCodes to two. This was done by implicitly
using the address family of the PCP message itself.
o New option THIRD_PARTY, to more carefully split out the case where
a mapping is created to a different host within the home.
o Integrated a lot of editorial changes from Stuart and Francis.
o Removed nested NAT text into another document, including the IANA-
registered IP addresses for the PCP server.
o Removed suggestion (MAY) that PCP server reserve UDP when it maps
TCP. Nobody seems to need that.
o Clearly added NAT and NAPT, such as in residential NATs, as within
scope for PCP.
o HONOR_EXTERNAL_PORT renamed to PREFER_FAILURE
o Added 'Lifetime' field to the common PCP header, which replaces
the functions of the 'temporary' and 'permanent' error types of
the previous version.
o Allow arbitrary Options to be included in PCP response, so that
PCP server can indicate un-supported PCP Options. Satisfies PCP
Issue #19
o Reduced scope to only deal with mapping protocols that have port
numbers.
o Reduced scope to not support DMZ-style forwarding.
o Clarified version negotiation.
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A.3. Changes from draft-ietf-pcp-base-02 to -03
o Adjusted abstract and introduction to make it clear PCP is
intended to forward ports and intended to reduce application
keepalives.
o First bit in PCP common header is set. This allows DTLS and non-
DTLS to be multiplexed on same port, should a future update to
this specification add DTLS support.
o Moved subscriber identity from common PCP section to MAP* section.
o made clearer that PCP client can reduce mapping lifetime if it
wishes.
o Added discussion of host running a server, client, or symmetric
client+server.
o Introduced PEER4 and PEER6 OpCodes.
o Removed REMOTE_PEER Option, as its function has been replaced by
the new PEER OpCodes.
o IANA assigned port 44323 to PCP.
o Removed AMBIGUOUS error code, which is no longer needed.
A.4. Changes from draft-ietf-pcp-base-01 to -02
o more error codes
o PCP client source port number should be random
o PCP message minimum 8 octets, maximum 1024 octets.
o tweaked a lot of text in section 7.4, "Opcode-Specific Server
Operation".
o opening a mapping also allows ICMP messages associated with that
mapping.
o PREFER_FAILURE value changed to the mandatory-to-process range.
o added text recommending applications that are crashing obtain
short lifetimes, to avoid consuming subscriber's port quota.
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A.5. Changes from draft-ietf-pcp-base-00 to -01
o Significant document reorganization, primarily to split base PCP
operation from OpCode operation.
o packet format changed to move 'protocol' outside of PCP common
header and into the MAP* opcodes
o Renamed Informational Elements (IE) to Options.
o Added REMOTE_PEER (for disambiguation with dynamic ports),
REMOTE_PEER_FILTER (for simple packet filtering), and
PREFER_FAILURE (to optimize UPnP IGD interworking) options.
o Is NAT or router behind B4 in scope?
o PCP option MAY be included in a request, in which case it MUST
appear in a response. It MUST NOT appear in a response if it
wasn't in the request.
o Response code most significant bit now indicates permanent/
temporary error
o PCP Options are split into mandatory-to-process ("P" bit), and
into Specification Required and Private Use.
o Epoch discussion simplified.
Authors' Addresses
Dan Wing (editor)
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, California 95134
USA
Email: dwing@cisco.com
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Stuart Cheshire
Apple, Inc.
1 Infinite Loop
Cupertino, California 95014
USA
Phone: +1 408 974 3207
Email: cheshire@apple.com
Mohamed Boucadair
France Telecom
Rennes, 35000
France
Email: mohamed.boucadair@orange-ftgroup.com
Reinaldo Penno
Juniper Networks
1194 N Mathilda Avenue
Sunnyvale, California 94089
USA
Email: rpenno@juniper.net
Francis Dupont
Internet Systems Consortium
Email: fdupont@isc.org
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