One document matched: draft-ietf-pcp-base-03.xml
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<rfc category="std" docName="draft-ietf-pcp-base-03" ipr="trust200902">
<front>
<title abbrev="Port Control Protocol (PCP)">Port Control Protocol
(PCP)</title>
<author fullname="Dan Wing" initials="D." surname="Wing">
<organization abbrev="Cisco">Cisco Systems, Inc.</organization>
<address>
<postal>
<street>170 West Tasman Drive</street>
<city>San Jose</city>
<region>California</region>
<code>95134</code>
<country>USA</country>
</postal>
<email>dwing@cisco.com</email>
</address>
</author>
<date />
<workgroup>PCP working group</workgroup>
<abstract>
<t>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.</t>
</abstract>
</front>
<middle>
<section anchor="introduction" title="Introduction">
<t>Port Control Protocol (PCP) provides a mechanism to control how
incoming packets are forwarded by upstream devices such as NAT64, NAT44,
and firewall devices. PCP is primarily designed to be implemented in the
context of both large scale NAT and small-scale NAT (e.g., residential
NATs). PCP allows hosts to operate servers permanently (e.g., a webcam)
or temporarily (e.g., while playing a game or on a phone call) when
behind one or more NAT devices, including when behind a large-scale NAT
operated by their Internet service provider.</t>
<t>PCP allows applications to create pinholes from an external IP
address 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 pinhole is created in the firewall. These pinholes are
required for successful inbound communications destined to machines
located behind a NAT.</t>
<t>After creating a pinhole 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.</t>
<t>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.</t>
<!--
> 1. define new IE, EVEN_PLUS_ONE, which has no payload.
>
> 2. PCP request is sent, with that IE.
>
> 3. PCP server attempts to allocate an even port number, and
> PCP server reserves the adjacent port number (sticks it
> on the TIME_WAIT queue for 5 seconds, and it is only allocatable
> to the same IP address as got the even port number).
>
> Maybe we have PCP server return an IE EVEN_PLUS_ONE if it
> was able to allocate the adjacent port. That seems helpful
> for the next steps.
>
> 4. VoIP endpoint can send its SIP/SDP message now. Total
> delay: one round trip to PCP server.
>
> 5. A second PCP request is sent, without the IE, requesting
> port+1.
>
> Med: I still we can avoid some extra exchanges with the server (for
> instance in your bullet 5, you will need to do it for all the media you
> are negotiating including audio, video, etc.).
If the endpoint needs to do audio and video, it will send two PCP
requests, at the same time, in step 2. This will result in two
PCP responses in step 4.
As soon as the audio+video session is established, there will be
at least 50 packets per second of video and ~20-50 packets per
second of video.
Here are the scenarios:
1. internal host is IPv4 only
2. internal host is IPv6 only
3. internal host is dual stack
For (1), that host can only do PIN44 (to get a public IPv4 address)
or PIN46 (to get a public IPv6 address).
For (2), that host can only do PIN66 (to get a public IPv6 address;
mostly this is for IPv6 firewall. Yes, this needs more fleshing
out. Yes, there is an "Ed. Note" to that effect in the document.
Yes, I am aware of that) or PIN64 (to get a public IPv4 address).
For (3), that host can use any of the four opcodes (PIN44, PIN46,
PIN64, PIN66). If it is being reasonable, it won't do PIN46
or PIN64, because it could just keep the IP address family the
same instead because it is dual stack. But we cannot detect
a dual-stack node and there isn't a reason to block it. So,
yes, I suppose a dual-stack host could attempt all four of
the OpCodes. But it would more reasonably do PIN44 to get
a public IPv4 presence and PIN66 to get a public IPv6 presence.
Besides, on a network with a dual-stack host, that network
is unlikely (not not prohibited) to operate a NAT64, and
also unlikely (but not prohibited) to operate a NAT46. This
seems to warrant some text around
In some scenarios communications may fail if intermediary (non
PCP-controlled) firewalls are not appropriately configured to accept
incoming traffic. Detecting the presence of firewall(s) in the path
and configuring it is out of scope of this document
Add discussion around if, to optimize keepalives, a host
should do PCP first or should do its TCP (or UDP) first.
If PCP is done first, the mapping will be endpoint independent.
If doing TCP (or UDP) first, the mapping could be endpoint
independent or could be endpoint dependent. This is all
tweakable with the PCP option ENDPOINT_DEPENDANT.
Add defintion, for firewall, of ENDPOINT_DEPENDANT. This allows
indicating an IPvM address (which, by necessity, matches the
length of the outside address of the PINxy), and optionally
allows indicating the remote protocol and remote port. Remote
protocol 0 means 'any protocol'. Remote port 0 means 'any
port'. Packets from the public Internet which don't match the
filter SHOULD get an ICMP error.
-->
<!--
-->
</section>
<section title="Scope">
<section title="Deployment Scenarios">
<t>PCP can be used in various deployment scenarios, including:<list
style="symbols">
<t><xref
target="I-D.ietf-softwire-dual-stack-lite">DS-Lite</xref>,
including a NAT and including a router behind the B4 element, and;
<list style="empty">
<t>[Ed. Note: Do we want 'NAT behind the B4 element' in our
scope? This affects PCP server discovery, among other things.
However, users deploy these NATs. Do we want PCP to work with
this, detect this, or quietly fail?? This is tracked as PCP
Issues #1 and #25 <xref target="PCP-Issues"></xref>.]</t>
</list></t>
<t>NAT64, both <xref
target="I-D.ietf-behave-v6v4-xlate-stateful">Stateful</xref> and
<xref target="I-D.ietf-behave-v6v4-xlate">Stateless </xref>,
and;</t>
<t><xref target="I-D.ietf-behave-lsn-requirements">Large-Scale
NAT44</xref>, including nested NATs ("NAT444"), and;</t>
<t><xref target="I-D.miles-behave-l2nat">Layer-2 aware NAT</xref>
and <xref target="I-D.arkko-dual-stack-extra-lite">Dual-Stack
Extra Lite</xref>, and;</t>
<t><xref target="I-D.ietf-v6ops-cpe-simple-security">IPv6 firewall
control</xref>.</t>
</list></t>
</section>
<section title="Supported Transport Protocols">
<t>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) can be wildcarded (allowing any traffic with that protocol
to pass), provided of course the upstream device being controlled by
PCP supports that functionality, or new PCP OpCodes can be defined to
support those protocols.</t>
</section>
<section anchor="mono_homed"
title="Single-homed Customer Premise Network">
<t>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 pinhole 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.</t>
</section>
</section>
<section anchor="terminology" title="Terminology">
<t>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 <xref
target="RFC2119">RFC 2119</xref>.</t>
<t><list style="hanging">
<t hangText="Port Forwarding:"><list style="empty">
<t>Port forwarding allows a host to receive traffic sent to a
specific IP address and port.</t>
<t>In the context of a NAT or NAPT, the internal address and
external address are different. In the context of a firewall,
the internal address and external address are different. 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. 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.</t>
<t>In the context of a firewall, the internal address, external
IP address, and ports are not changed.</t>
</list></t>
<t hangText="PCP Client:"><list style="empty">
<t>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 PCP to PCP (for nested NATs) is another example of a PCP
client.</t>
</list></t>
<t hangText="PCP Server:"><list style="empty">
<t>A network element which receives and processes PCP requests
from a PCP Client. See also <xref
target="relationship"></xref>.</t>
</list></t>
<t hangText="Mapping:"><list style="empty">
<t>See also Port Forwarding. A mapping exists only in the
context of a Network Address Translator. 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.</t>
</list></t>
<t hangText="Mapping Types:"><list style="empty">
<t>There are three different ways to create mappings: dynamic
(e.g., outgoing TCP SYN), PCP, and static configured (e.g., CLI
or web page). These mappings are one and the same but their
attributes such as lifetime or filtering might be different.</t>
</list></t>
<t hangText="Interworking Function:">a functional element
responsible for interworking another protocol with PCP. For example
interworking between <xref target="IGD">UPnP IGD</xref> with
PCP.</t>
<t hangText="subscriber:">an entity provided access to the network.
In the case of a commercial ISP, this is typically a single
home.</t>
<t hangText="host:">a device which can have packets sent to it, as a
result of PCP operations. A host is not necessarily a PCP
client.</t>
</list></t>
</section>
<section anchor="relationship"
title="Relationship of PCP Server and its NAT">
<t>The PCP server receives PCP requests. The PCP server might be
integrated within the NAT or firewall device (as shown in <xref
target="diagram_pcp_server_embedded"></xref>) which is expected to be a
common deployment.</t>
<figure anchor="diagram_pcp_server_embedded"
title="device with Embedded PCP Server">
<artwork align="center"><![CDATA[ +-----------------+
+------------+ | NAT or firewall |
| PCP Client |-<network>-+ +---<Internet>
+------------+ | with embedded |
| PCP server |
+-----------------+]]></artwork>
</figure>
<t>However, it is useful to also model a separation of the PCP server
from the NAT, as shown below (<xref
target="diagram_pcp_server_separate"></xref>). The PCP server would
communicate with the NAT using a protocol beyond the scope of this
document, such as a proprietary protocol or any suitable standard
protocol for NAT control.</t>
<figure anchor="diagram_pcp_server_separate"
title="NAT with Separate PCP Server">
<artwork align="center"><![CDATA[ +-----------------+
+--+ NAT or firewall +---<Internet>
/ +-----------------+
+------------+ / ^
| PCP Client +-<network> | any suitable control protocol
+------------+ \ v
\ +------------+
+--+ PCP Server |
+------------+
]]></artwork>
</figure>
</section>
<section title="Common Request and Response Header Format">
<t>All PCP messages contain a request (or response) header, opcode-
specific information, and 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 <xref target="pin_opcodes"></xref> and <xref
target="peer_opcodes"></xref>.</t>
<section title="Request Header">
<figure align="left" anchor="common_request"
title="Common Request Packet Format">
<preamble>All requests have the following format:</preamble>
<artwork align="center"><![CDATA[
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|Ver=0|reserve|R| OpCode | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Reserved (48 bits) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: (optional) opcode-specific information :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: (optional) PCP Options :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>These fields are described below:<list style="hanging">
<t hangText="1">A single bit set to 1.</t>
<t hangText="Ver:">Version is 0</t>
<t hangText="reserve:">4 reserved bits, MUST be sent as 0 and MUST
be ignored when received.</t>
<t hangText="R:">Indicates Request (0) or Response (1). All
Requests MUST use 0.</t>
<t hangText="OpCode:">Opcodes are defined in <xref
target="pin_opcodes"></xref> and <xref
target="peer_opcodes"></xref>. New OpCodes can be defined per
rules described in <xref target="iana"></xref>.</t>
<t hangText="Reserved:">48 reserved bits, MUST be sent as 0 and
MUST be ignored when received.</t>
</list></t>
</section>
<section title="Response Header">
<figure align="left" anchor="common_response"
title="Common Response Packet Format">
<preamble>All responses have the following format:</preamble>
<artwork align="center"><![CDATA[
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|Ver=1|reserve|R| Opcode | Reserved | Result Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Epoch |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: (optional) OpCode-specific response data :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: (optional) Options :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>These fields are described below:<list style="hanging">
<t hangText="Ver:">Version is 1</t>
<t hangText="reserve:">4 reserved bits, MUST be sent as 0, MUST be
ignored when received.</t>
<t hangText="R:">Indicates Request (0) or Response (1). All
Responses MUST use 1.</t>
<t hangText="OpCode:">The OpCode value from the request.</t>
<t hangText="OpCode:">8 reserved bits, MUST be sent as 0, MUST be
ignored when received.</t>
<t hangText="Result Code:">The result code for this response. See
<xref target="result_codes"></xref> for values.</t>
<t hangText="Epoch:">The server's Epoch value. The same value is
used for all PCP clients. See <xref target="epoch"></xref> for
discussion.</t>
</list></t>
</section>
<section anchor="pcp_information_elements" title="Options">
<t>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 markings to apply
to incoming or outgoing traffic associated with a PCP pinhole, or an
Open could include descriptive text (e.g., "for my webcam").</t>
<t>Options use the following Type-Length-Value format:</t>
<figure align="left" anchor="options-layout" title="Options Header">
<artwork align="center"><![CDATA[ 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 :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>The description of the fields is as follows:<list style="hanging">
<t hangText="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 <xref
target="iana"></xref>.</t>
<t hangText="Reserved:">MUST be set to 0 on transmission and MUST
be ignored on reception.</t>
<t hangText="Option-Length:">Indicates in units of 4 octets the
length of the enclosed data. Options with length of 0 are
allowed.</t>
<t hangText="data:">Option data. The option data MUST end on a 32
bit boundary, padded with 0's when necessary.</t>
</list></t>
<t>A given Option MAY be included in a request. An Option MUST NOT
appear in a PCP response unless solicited in the associated request.
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 Server MUST be specified
in a 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 response. If several Options are included in a PCP
request or response, they can be encoded in any order by the PCP
client. The response MUST encode them in the same order, but may omit
some PCP Options in the response (e.g., omitting them is necessary to
indicate the PCP server does not understand that Option, or simply
because that Option is not included in responses). A single Option MAY
appear more than once, 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, the PCP server MUST respond with the
MALFORMED_OPTION response code.</t>
<t>If the "P" bit in the OpCode is set, <list style="symbols">
<t>the PCP server MUST only generate a positive PCP response if it
can successfully process the PCP request and this Option.</t>
<t>if the PCP server does not implement this Option, it MUST
generate a failure response without including this Option in the
response.</t>
<t>If the PCP server does implement this Option, but cannot
perform the function indicated by this Option, it MUST generate a
failure response and include this Option (and its arguments) in
the response.</t>
</list></t>
<t>If the "P" bit is clear, the PCP server MAY process or ignore this
Option.</t>
<t>To enhance interoperability, newly defined Options should avoid
interdependencies with each other.</t>
<t>New Options MUST include the information below:</t>
<t><list style="empty">
<t>This Option:<list style="empty">
<t>name: <mnemonic></t>
<t>number: <value></t>
<t>purpose:</t>
<t>is valid for OpCodes: <list of OpCodes></t>
<t>has length: <rules for length></t>
<t>appear more than once: <yes/no></t>
</list></t>
</list></t>
</section>
<section anchor="result_codes" title="Result Codes">
<t>The following result codes may be returned as a result of any
OpCode received by the PCP server. Result codes are 8 bits long and
the most significant bit indicates if the error is transient or
permanent. A transient error is one that might resolve itself, such
that an identical PCP request submitted later would be successful
(e.g., a resource is consumed and might become available later). A
permanent error is one that cannot reasonably be successful if an
identical PCP request is submitted (e.g., re-sending a PCP request
containing an OpCode the server does not support). Future result codes
should follow this same format.</t>
<figure anchor="figure_result_codes" title="PCP Result Codes">
<artwork align="center"><![CDATA[
0 - SUCCESS, success
128 - UNSUPP_VERSION, unsupported version
129 - UNSUPP_OPCODE, unsupported OpCode
130 - UNSUPP_OPTION, unsupported Option
131 - MALFORMED_OPTION, malformed Option (e.g., exists too many
times, invalid length)
132 - UNSPECIFIED_ERROR, server encountered unspecified error
133 - MALFORMED_REQUEST
]]></artwork>
</figure>
<t>Additional result codes, specific to the OpCodes defined in this
document, are listed in <xref
target="pin-opcode-specific-result-codes"></xref> and <xref
target="peer-opcode-specific-result-codes"></xref> .</t>
</section>
</section>
<section title="General PCP Operation">
<t>PCP messages MUST be sent over UDP, and the PCP Server MUST listen
for PCP requests on the PCP port number (<xref
target="iana_port"></xref>). Every PCP request generates a response, so
PCP does not need to run over a reliable transport protocol.</t>
<section title="General PCP Client Operation">
<t>This section details operation specific to a PCP client, for any
OpCode. Procedures specific to the PIN OpCodes are described in <xref
target="pin_opcodes"></xref>, and procedures specific to the PEER
OpCodes are described in <xref target="peer_opcodes"></xref>.</t>
<section anchor="sec_generating_request"
title="Generating and Sending a Request">
<t>Prior to sending its first PCP message, the PCP client determines
which servers to use. The PCP client tries the following to get a
list of PCP servers:<list style="numbers">
<t>if a PCP server is configured (e.g., in a configuration
file), the address(es) of the PCP server(s) are used as the list
of PCP server(s), else;</t>
<t>if DHCP indicates the PCP server(s), the address(es) of the
indicated PCP server(s) are used as the list of PCP server(s),
else;</t>
<t>if the PCP working group decides an IANA-allocated address
for the PCP server is suitable, it is added to the list of PCP
servers, else;</t>
<t>the address of the default router, it is added to the list of
PCP servers.</t>
</list><list style="empty">
<t>[Ed. Note: more discussion around these methods is necessary
to reach consensus on the best approach(es) for PCP. Also see
<xref target="discovery_analysis"></xref> for further analysis.
This is tracked as PCP Issue #1 <xref
target="PCP-Issues"></xref>.]</t>
</list></t>
<t>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. When several PCP Clients are embedded in the
same host, each uses a distinct 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 <xref target="RFC5461"></xref> for discussion 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, no PCP
server has responded the PCP client SHOULD abort the procedure.</t>
<t>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.</t>
</section>
<section title="Processing a Response">
<t>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 8 octets, longer than 1024 octets,
or not a multiple of 4 octets are invalid and ignored. 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 <xref target="epoch"></xref>).</t>
<t>If it is an error response (>0), the request failed. If the
error response is less than 128, retrying the same request sometime
in the future might be successful. If the error response is greater
or equal to 128, retrying the same request is unlikely to be
successful.</t>
<t>If it is the success response (0), the PCP client knows the
request was successful.</t>
</section>
<section anchor="mif" title="Multi-interface Issues">
<t>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, <xref
target="RFC4193"></xref>)).</t>
<t>IPv6 addresses with global reachability scope SHOULD be used as
internal IP address when instructing 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.</t>
<t>As mentioned in <xref target="mono_homed"></xref>, only
mono-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. <list
style="empty">
<t>[Ed. Note: text regarding multi-homing needs work.]</t>
</list></t>
<!--
Section 2.4, "Change of the Internal IP Address"
When a new IP address is assigned to a host embedding a PCP Client,
the PCP Client MUST install on the PCP Server all the mappings it
manages, using the new assigned IP address as the internal IP
address.
This needs some additional discussion. Let's take an example where
I have a computer with both WiFi and wired Ethernet connections
and I plug and unplug the Ethernet connection, or go in and out
of range of WiFi. When do we want PCP to do something about
that change of connectivity? Does the answer depend on IPv4,
IPv6, or dual stack running on that interface if we're doing PIN44,
PIN64, PIN46, PIN66?
Med: Good point. IMHO, the address selection should be done according to the-be-completed section: http://tools.ietf.org/html/draft-ietf-pcp-base-02#section-6.1.3. Based on the output of that process, the PCP Client can be triggered accordingly.
Or ... just recommend the internal IP address not be changed!
-->
</section>
<section anchor="epoch" title="Epoch">
<t>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 port mapping table, due to reboot,
power failure, or any other reason, it MUST reset its Epoch time to
0. Similarly, if the public IP address of the NAT (controlled by the
PCP server) changes, the Epoch MUST be reset to 0.</t>
<t>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 <xref target="reboot"></xref>.<list style="empty">
<t>[Ed. Note: comment from Dave Thaler: "So spoofed packets with
Epoch=0 that look like they come from the server could result in
a big amplification attack on the PCP server. How is this
mitigated?". This is tracked as PCP Issue #21, <xref
target="PCP-Issues"></xref>.]</t>
</list></t>
</section>
</section>
<section title="General PCP Server Operation">
<t>This section details operation specific to a PCP server.</t>
<t>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.</t>
<t>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 version number of the request with the UNSUPP_VERSION response
code. 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, a response is generated with
the MALFORMED_REQUEST response code, the response 0-filled to be a
multiple of 4 octets and not to exceed 1024 octets.</t>
</section>
</section>
<section title="Introduction to PIN and PEER OpCodes">
<t>There are three uses for the PIN 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
application keepalive traffic), and a host operating a client and server
on the same port. These are discussed in the following sections.</t>
<t>When operating a server (<xref target="operating_a_server"></xref>
and <xref target="pcp_symmetric"></xref>) the PCP client knows if it
wants an IPv4 listener (PINx4), IPv6 listener (PINx6), or both (PINx4
and PINx6) on the Internet. The PCP client also knows if it has an IPv4
interface on itself (PIN4y) or an IPv6 interface on itself (PIN4y). It
takes the union of this knowledge to decide to send a request for PIN44,
PIN64, PIN46, or PIN66. Applications that embed IP addresses in payloads
(e.g., FTP, SIP) will find it beneficial to avoid address family
translation (PIN46, PIN64), if possible.</t>
<!--
<t>On many common platforms (i.e., those making use of the BSD sockets
API), using PCP for purposes of application keepalives by issuing a
PCP request followed by a dynamic connection to the server is
difficult to implement properly. This is therefore NOT RECOMMENDED.
Instead, client applications SHOULD first establish a dynamic
connection to a server, and then issue a PCP request related to that
connection, including the REMOTE_PEER option.</t>
-->
<section anchor="operating_a_server" title="For Operating a Server">
<t>A host operating a server (e.g., a web server) listens for traffic
on a port (but never sends traffic from that port. For this to work
across a NAT or a firewall, the application needs to (a) create a
pinhole from a public IP address and port to itself as described in
<xref target="pin_opcodes"></xref> 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.</t>
<t>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 PIN OpCode depending on if it is listening on an IPv4 or
IPv6 interface and if it wants a public IPv4 or IPv6 address.</t>
<figure anchor="fig_operate_server"
title="Pseudo-code for using PCP to operate a server">
<preamble>The following pseudo-code shows how PCP can be reliably
used to operate a server:</preamble>
<artwork align="center"><![CDATA[
/* start listening on the local server port */
int s = socket(...);
bind(s, &sockaddr, ...);
listen(s, ...);
getsockname(s, &internal_address, ...);
external_address = NUL;
pcp_send_pin_request(internal_address, &external_address, lifetime);
update_rendezvous_server("Client 12345", external_address);
while (1) {
accept(s, ...);
/* ... */
} ]]></artwork>
<postamble></postamble>
</figure>
</section>
<section anchor="keepalives" title="For Reducing NAT Keepalive Messages">
<t><list style="empty">
<t>[Ed. Note: This section creates a difference between a
dynamically-created mapping, which PCP tries to query/control
using the PEER OpCode, and a PCP-created mapping which was created
with a PIN OpCode. This section attempts to address PCP Issue #9
and PCP Issue #35.]</t>
</list></t>
<t>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.</t>
<t>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 avoid such application
keepalive traffic by using PCP. <list style="empty">
<t>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.</t>
</list></t>
<t>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 <xref
target="peer_opcodes"></xref>. 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.</t>
<figure anchor="fig_keepalive_pseudocode"
title="Pseudo-code using PCP with a dynamic socket">
<preamble>The following pseudo-code shows how PCP can be reliably
used with a dynamic socket, for the purposes of reducing application
keepalive messages:</preamble>
<artwork align="center"><![CDATA[
int s = socket(...);
connect(s, &remote_peer, ...);
getsockname(s, &internal_address, ...);
external_address = NUL;
pcp_send_peer_request(internal_address, &external_address,
remote_peer, lifetime);
]]></artwork>
</figure>
</section>
<section anchor="pcp_symmetric"
title="For Operating a Symmetric Client/Server">
<t><list style="empty">
<t>[Ed. Note: The PEER4 and PEER6 OpCodes, discussed here, are
intended to resolve PCP Issue #35.]</t>
</list></t>
<t>A host operating a client and server on the same port (e.g., <xref
target="RFC4961">Symmetric RTP</xref> or <xref target="RFC3581">SIP
Symmetric Response Routing (rport)</xref>) 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. For accomplish this, the application uses the procedure
described in this section.</t>
<t>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 PIN OpCode, as described in <xref
target="pin_opcodes"></xref>, and receive a positive PCP response
before it sends any packets from that port. 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
outgoing dynamic connection and the PIN OpCode will cause different
ports to be assigned (which is not desirable; after all, the
application is using the same port for outgoing and incoming traffic
on purpose) and they will also have different lifetimes. As a
reminder, 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 outbound connection will be EIM or non-EIM.</t>
<!--
<list style="empty">
<t>[[Ed. Note: And also reversing the steps is complex and
fragile. Do we want to additionally mention the fragility? I
think we don't need to mention the fragility. Reference
http://www.ietf.org/mail-archive/web/pcp/current/msg00474.html.]]</t>
</list></t>
-->
<figure anchor="fig_pseudocode_symmetric"
title="Pseudo-code for using PCP to operate a symmetric client/server">
<preamble>The following pseudo-code shows how PCP can be used to
operate a symmetric client and server:</preamble>
<artwork align="center"><![CDATA[
/* start listening on the server port */
int s = socket(...);
bind(s, &sockaddr, ...);
listen(s, ...);
getsockname(s, &internal_address, ...);
external_address = NUL;
pcp_send_pin_request(internal_address, &external_address, lifetime);
update_rendezvous_server("Client 12345",external_address);
/* ... */
send_packet(s, "Hello World");
]]></artwork>
<postamble></postamble>
</figure>
</section>
</section>
<section anchor="pin_opcodes" title="PIN OpCodes">
<t>This section defines four OpCodes which forwarding from a NAT (or
firewall) to an internal host. They are: <list hangIndent="10"
style="hanging">
<t hangText="PIN44=0:">create a forwarding pinhole between an
internal IPv4 address and public IPv4 address (e.g., NAT44 or
firewall)</t>
<t hangText="PIN46=1:">create a forwarding pinhole between an
internal IPv4 address and public IPv6 address (e.g., NAT46 or
firewall)</t>
<t hangText="PIN64=2:">create a forwarding pinhole between an
internal IPv6 address and public IPv4 address (e.g., NAT64 or
firewall)</t>
<t hangText="PIN66=3:">create a forwarding pinhole between an
internal IPv6 address and public IPv6 address (e.g., NPTv6 or
firewall)</t>
</list></t>
<t>The operation of these OpCodes is described in this section.</t>
<section title="OpCode Packet Formats">
<t>The four PIN OpCodes (PIN44, PIN46, PIN64, PIN66) share a similar
packet layout for both requests and responses. Because of this
similarity, they are shown together. For all of the PIN OpCodes, if
the internal IP address and internal port fields of the request both
match the response's external IP address and external port fields, 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.</t>
<t>The following diagram shows the request packet format for PIN44,
PIN46, PIN64, and PIN66. This packet format is aligned with the
response packet format:</t>
<figure align="center" anchor="pin_request"
title="PIN OpCode Request Packet Format">
<preamble></preamble>
<artwork><![CDATA[
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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Pinhole Internal IP address (32 or 128, depending on OpCode) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Requested external IP address (32 or 128, depending on OpCode):
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Requested lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| internal port | requested external port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>These fields are described below:<list style="hanging">
<t hangText="Protocol:">indicates protocol associated with this
OpCode. Values are taken from the <xref
target="proto_numbers">IANA protocol registry</xref>. For example,
this field contains 6 (TCP) if the opcode is intended to create a
TCP mapping.</t>
<t hangText="Reserved:">24 reserved bits, MUST be 0 on
transmission and MUST be ignored on reception.</t>
<t hangText="Pinhole Internal IP Address:">Internal IP address of
the pinhole. This can be IPv4 or IPv6, depending on the
OpCode.</t>
<t hangText="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.</t>
<t hangText="Requested lifetime:">Requested lifetime of this
pinhole, in seconds.</t>
<t hangText="internal port:">Internal port for the pinhole.</t>
<t hangText="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 MUST use 0.</t>
</list></t>
<t>The following diagram shows the response packet format for PIN44,
PIN46, PIN64, and PIN66:</t>
<figure align="center" anchor="pin_response"
title="PIN OpCode Response Packet Format">
<preamble></preamble>
<artwork><![CDATA[
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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Pinhole Internal IP address (32 or 128, depending on OpCode) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Assigned external IP address (32 or 128, depending on OpCode) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Assigned lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| internal port | assigned external port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>These fields are described below:<list style="hanging">
<t hangText="Protocol:">Copied from the request.</t>
<t hangText="Reserved:">24 reserved bits, MUST be 0 on
transmission, MUST be ignored on reception.</t>
<t hangText="Pinhole Internal IP address:">Copied from the
request. IPv4 or IPv6 address is indicated by the OpCode.</t>
<t hangText="Assigned external IP address:">Assigned external IPv4
or IPv6 address for the pinhole. IPv4 or IPv6 address is indicated
by the OpCode</t>
<t hangText="Assigned Lifetime:">Lifetime for this mapping, in
seconds</t>
<t hangText="Internal port:">Internal port for the pinhole, copied
from request.</t>
<t hangText="Assigned external port:">requested external port for
the mapping. IPv4 or IPv6 address is indicated by the OpCode</t>
</list></t>
</section>
<section anchor="pin-opcode-specific-result-codes"
title="OpCode-Specific Result Codes">
<t>In addition to the result codes described in <xref
target="figure_result_codes"></xref>, the following additional result
codes may be returned as a result of the four PIN OpCodes received by
the PCP server.</t>
<figure anchor="figure_pin_result_codes"
title="Result Codes specific to PIN OpCodes">
<artwork align="center"><![CDATA[
3 - NETWORK_FAILURE, e.g., NAT device has not obtained a DHCP
lease
4 - 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.
150 - UNSUPP_PROTOCOL, unsupported Protocol
151 - NOT_AUTHORIZED, e.g., PCP server supports mapping, but the
feature is disabled for this PCP client, or the PCP client
requested a pinhole that cannot be fulfilled by the PCP
server's security policy.
152 - USER_EX_QUOTA, mapping would exceed user's port quota
153 - CANNOT_HONOR_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
HONOR_EXTERNAL_PORT.
154 - UNABLE_TO_DELETE_ALL, indicates the PCP server was not able
to delete all pinholes.
155 - CANNOT_FORWARD_PORT_ZERO, indicates the requested external
port 0 cannot be fulfilled, because the PCP-controlled
device is a firewall.
]]></artwork>
</figure>
<t>Other OpCodes are in result codes are defined following the
procedure in <xref target="iana_result_codes"></xref>.</t>
</section>
<section anchor="pin-opcode_client_operation"
title="OpCode-Specific Client Operation, Processing a Response">
<t>This section describes the operation of a client when sending the
OpCodes PIN44, PIN64, PIN46, or PIN66.</t>
<t>A response is matched with a request by comparing the protocol,
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 pinhole created
by the OpCode.</t>
<t>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.</t>
<t>If an unsuccessful result code greater than or equal to 128, the
PCP client SHOULD NOT re-issue the same request. If a result code less
than or equal to 127, the PCP client MAY, if it wishes, resend the
same message after a delay of at least 5 seconds.</t>
<!--
<t>[Ed. Note: remove this paragraph: The PCP client might receive the
AMBIGIOUS response code if its request did not include the REMOTE_PEER
option. If the PCP client is attempting to query (or control) the
lifetime of a dynamic connection, the client should include the
REMOTE_PEER option, as described in <xref target="keepalives"></xref>.
If the PCP client is attempting to establish a pinhole to that port
(that is, operate a server), the client cannot include the REMOTE_PEER
option; instead, the client has to choose a different internal port
and send a new PCP request specifying that port. ]</t>
-->
</section>
<section anchor="pin-opcode_server_operation"
title="OpCode-Specific Server Operation">
<t>This section describes the operation of a client when processing
the OpCodes PIN44, PIN64, PIN46, or PIN66.</t>
<t>If the requested lifetime is 0, it indicates a request to delete
the pinhole immediately. This means the pinhole described by the
internal IP address should be deleted, and requested external port
field is ignored by the server (that is, it isn't validated). If the
deletion request was properly formatted, and the associated pinhole
(if present) is deleted, a positive response is generated containing
external port of 0 and lifetime of 0. If the client attempts to delete
a port mapping which was manually assigned by some kind of
configuration tool, the PCP server MUST respond with NOT_AUTHORIZED
result code. <list style="empty">
<t>[Ed. Note: Should we similarly return an error if attempting to
delete mappings that were created dynamically (e.g., TCP SYN)?]
This is tracked as PCP Issues #9 <xref
target="PCP-Issues"></xref>.]</t>
</list></t>
<t>A PCP client can request the explicit deletion of all UDP or TCP
mappings by sending a PCP request with a PIN OpCode with external
port, internal port, and lifetime set to 0. A PCP client MAY choose to
do this when it first acquires a new IP address in order to protect
itself from port mappings that were performed by a previous owner of
the IP address. After receiving such a deletion request, the PCP
server and its PCP-controlled device MUST delete all the port
mappings. The PCP server responds to such a deletion request with a
response as described above, with the internal port set to zero. If
the PCP server is unable to delete a port mapping, for example,
because the mapping was manually configured by a configuration tool,
the PCP server MUST still delete as many port mappings as possible,
and respond with the result code UNABLE_TO_DELETE_ALL.</t>
<t>See <xref target="pin-pinhole_lifetime"></xref> for processing the
lifetime.</t>
<t>If the requested external port is 0, and the PCP-controlled device
does not change port numbers (that is, it does not do port
translation), it cannot fulfill the request. In that case, the PCP
server MUST return the response code CANNOT_FORWARD_PORT_ZERO.</t>
<t>If the PCP-controlled device is stateless (that is, does not
establish any per-flow state), the PCP server simply returns an
answer, without creating any "pinholes".</t>
<t>If an option with value greater than 128 exists but that option
does not make sense (e.g., the HONOR_EXTERNAL_PORT option is included
in a request with lifetime=0 (indicating a delete request)), the
request is invalid and generates a MALFORMED_OPTION error.</t>
<!--
<t>If the REMOTE_PEER option is not included in the request and it is
impossible for the PCP-controlled device to establish a pinhole
because a conflicting dynamic mapping already exists, the PCP server
responds with the error AMBIGUOUS (this is due to interactions with
dynamic pinholes, see <xref target="dynamic-interaction"></xref>).</t>
-->
<t>By default, a PCP-controlled device MUST NOT create pinholes 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. Nevertheless, a
configurable feature MAY be supported by the PCP-controlled device,
which MAY reserve (but not forward) the companion port so the same PCP
Client can request it in the future.</t>
<t>The PCP server then validates that the internal IP address in the
PIN OpCode belongs to the same subscriber. This validation depends on
the PCP deployment scenario; see <xref
target="subscriber_identification"></xref> 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.</t>
<t>If all of the proceeding operations were successful (did not
generate an error response), then the requested pinholes 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.</t>
<t>As a side-effect of creating a pinhole, ICMP messages associated
with the pinhole are also translated (if appropriate) and forwarded
for the duration of the pinhole'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 pinholes for those flows.</t>
<section title="Maintaining Same External IP Address">
<t>If there are active mappings associated with a given subscriber
(see <xref target="subscriber_identification"></xref>) -- created
via dynamic assignment, by PCP or any other means -- subsequent PCP
mapping requests belonging to the same subscriber MUST use the same
external IP address. This follows the intent of REQ-1 of <xref
target="I-D.ietf-behave-lsn-requirements"></xref>.</t>
<t>Once an internal host has no active mapping in the PCP-controlled
device, a subsequent PCP request for that host MAY be assigned to a
different external IP address.</t>
</section>
<section anchor="pin-pinhole_lifetime" title="Pinhole Lifetime">
<t>The PCP Client requests a certain lifetime, and the PCP Server
responds with the assigned lifetime. The PCP Server can minimize and
maximize 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
long 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.</t>
<t>Once a PCP server has responded positively to a pinhole 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).</t>
<t>An application that forgets its PCP-assigned mappings (e.g., the
application or OS crashed) will request new PCP mappings (consuming
the user's port quota (if there is a quota) and the resource limit
for number of pinholes), and the application will also probably
initiate dynamic connections to servers without using PCP (also
consuming the user's port 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.</t>
</section>
<section anchor="pin-sec_server_delete" title="Pinhole Deletion">
<t>A pinhole MUST be deleted by the PCP Server upon the expiry of
its lifetime, or upon request from the PCP client.</t>
<t>In order to prevent another subscriber from receiving unwanted
traffic, the PCP server SHOULD NOT assign that same external port to
another host for 120 seconds (MSL, <xref
target="RFC0793"></xref>).</t>
<t><list style="empty">
<t>[Ed. Note: it should (MUST?) allow the same host to
re-acquire the same port, though.]</t>
</list></t>
</section>
<section title="Subscriber Renumbering">
<t>The customer premise 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 (old)
address -- both traffic mapped with PIN requests and dynamic
traffic. This same problem can occur if an IP address is re-assigned
today, without PCP. The solution is the same as today: ISPs should
not re-assign IP addresses to different subscribers.</t>
<t>When a new IP 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. The requested external port field will not be honored by
the PCP server, in all likelihood, because it is still being
forwarded to the old IP address. Thus, a pinholes is likely to be
assigned a new external port number and/or public IP address.</t>
</section>
</section>
<section anchor="pin_options" title="PCP Options for PIN OpCodes">
<!--
<section title="EVEN_PLUS_ONE">
<t><xref target="RFC3550">RTP</xref> has historically used an
even-numbered port, and RTCP the next-higher port (often abbreviated
as "port + 1"). Some equipment still expects RTP/RTCP on adjacent
ports. To accommodate that, the PCP Option EVEN_PLUS_ONE can be used
by the PCP client and server, with the following procedure.</t>
<t><list style="empty">
<t>[Ed. Note: Are there any other protocols that need adjacent
ports?]</t>
</list></t>
<t>The procedure is for the PCP client to bind to two ports on its
local interface. It then sends a PCP request for external port 0
(indicating it will accept any port from the server) for one of those
internal ports and includes the PCP Option EVEN_PLUS_ONE with this
request. If the server understands this option, it will choose an
even-numbered external port and will reserve the next-higher port with
a short timeout (suggested duration is 10 seconds) for this same PCP
client to allocate in a subsequent PCP request. The PCP server sends a
response and indicates it performed that operation by including the
PCP Option EVEN_PLUS_ONE in the response. The PCP client then sends a
second PCP request for the next-higher external port. Refreshing and
deleting the ports works as normal.</t>
<figure anchor="even_plus_one_message_flow"
title="Message Flow, EVEN_PLUS_ONE">
<preamble>A diagram of the message flow:</preamble>
<artwork align="center"><![CDATA[
PCP Client PCP Server
| |
|....request ext-port=0, EVEN_PLUS_ONE....>|
|<.response ext-port=23456, EVEN_PLUS_ONE..|
|....request ext-port=23457...............>|
|<-response ext-port=23457.................|
| |
]]></artwork>
</figure>
<t>The PCP Option EVEN_PLUS_ONE always has an Option-Length of 0. When
the PCP client wants an even-numbered port and the next-higher
adjacent port, it includes the PCP Option EVEN_PLUS_ONE in its PCP
request. If the server understands the option, has successfully mapped
an even-numbered external-port, and temporarily reserved the
next-higher port for this PCP client, the server MUST include the
EVEN_PLUS_ONE Option in its response. If the server understands the
option, but was unsuccessful at mapping an even-numbered port or
unsuccessful at temporarily reserving the next-higher port for this
PCP client, the server MUST NOT include the EVEN_PLUS_ONE Option in
its response. If the server receives a PCP request with the
EVEN_PLUS_ONE option for an odd-numbered requested-external-port, it
MUST return an error.</t>
<t>This Option is permitted with the following OpCodes: PIN44, PIN64,
PIN46, PIN66.</t>
</section>
-->
<section anchor="remote_peer_filter" title="REMOTE_PEER_FILTER">
<t>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.
That is, packets with a source IP address, transport, or port that
do not match those fields of the PCP request are dropped by the PCP
server-controlled NAT/firewall device.</t>
<figure>
<artwork align="center"><![CDATA[ 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 | Remote Peer Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Remote Peer IP address (32 bits if PIN44 or PIN64, :
: 1 28 bits if PIN46 or PIN66) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
</figure>
<t><list style="empty">
<t>This Option:<list style="empty">
<t>value: 128</t>
<t>is valid for OpCodes: PIN44, PIN64, PIN46, or PIN66</t>
<t>is included in responses: MUST</t>
<t>has length: 2 or 5</t>
<t>may appear more than once: no</t>
</list></t>
</list>Because of interactions with dynamic ports this Option MUST
only be used by a client that is operating a server, 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 <xref
target="RFC3424"></xref> to fail where they would have otherwise
succeeded, breaking other applications running on this same
host.</t>
<t><list style="empty">
<t>[Ed. Note: How do we want to remove a filter? Do we want to
allow removing a filter at all -- is there a use-case for that
or can the application just create a new mapping? If we have a
use-case, perhaps use 0.0.0.0 as the remote IP address to remove
all filters? This is tracked as PCP Issue #10 <xref
target="PCP-Issues"></xref>.]</t>
</list></t>
</section>
<!--
<section title="REMOTE_PEER">
<t>Due to a pre-existing dynamic mapping, a PCP server may not be
able to instantiate a filter on a specific port. It is thus
recommended that applications bind to the source port (to prevent
other applications from using that same source port) prior to using
this PCP Option.</t>
<t>In those situations, the Option REMOTE_PEER is necessary to
disambiguate the mappings. This option does not change filtering
behavior of the NAT or firewall.</t>
<figure>
<artwork align="center"><![CDATA[ 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 | Remote Peer Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Remote Peer IP address (32 bits if PIN44 or PIN64, :
: 1 28 bits if PIN46 or PIN66) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
</figure>
<t><list style="empty">
<t>This Option:<list style="empty">
<t>value: 129</t>
<t>is valid for OpCodes: PIN44, PIN64, PIN46, or PIN66</t>
<t>is included in responses: MUST</t>
<t>has length: 2 or 5</t>
<t>may appear more than once: no</t>
</list></t>
</list></t>
</section>
-->
<section title="HONOR_EXTERNAL_PORT">
<t>This option indicates the PCP client needs to have the indicated
requested external port allocated. If the PCP server cannot provide
that port for the exclusive use of the PCP client, the PCP server
MUST return result code CANNOT_HONOR_EXTERNAL_PORT.</t>
<t>This option is intended for use by <xref
target="upnp-interworking">UPnP IGD interworking</xref>.</t>
<t><list style="empty">
<t>This Option:<list style="empty">
<t>value: 130</t>
<t>is valid for OpCodes: PIN44, PIN64, PIN46, or PIN66</t>
<t>is included in responses: MUST</t>
<t>has length: 0</t>
<t>may appear more than once: no</t>
</list></t>
</list></t>
</section>
</section>
<section title="PCP Mapping State Maintenance">
<t>If an event occurs that causes the PCP server to lose state (such
as a crash or power outage), the pinholes 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.</t>
<t>The Epoch indicates if the PCP server has lost its state. If this
occurs, the PCP client can attempt to recreate the pinholes following
the procedures described in this section.</t>
<section anchor="reboot" title="Recreating Pinholes">
<t>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).</t>
<t>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 <xref
target="epoch"></xref>).</t>
<t>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.</t>
<t>This self-healing property of the protocol is very important.</t>
<t>When a client renews its port mappings as the result of receiving
a packet where the Epoch field indicates that a reboot or similar
loss of state has occurred, the client MUST first delay by a random
amount of time selected with uniform random distribution in the
range 0 to 5 seconds, and then send its first PCP request. After
that request is acknowledged by the PCP server, the client may then
send its second request, and so on, as rapidly as the gateway
allows. The requests SHOULD be issued serially, one at a time; the
client SHOULD NOT issue multiple requests simultaneously in
parallel.</t>
<t><list style="empty">
<t>[Ed. Note: the paragraph above is copied from NAT-PMP, and
seems to be advice specific to receiving asynchronous
notification that the Epoch was reset. Asynchronous notification
needs the delay described (in fact, it probably needs greater
delay than 0-5 seconds if on a larger network) and also needs to
discourage sending multiple PCP requests serially. However, PCP
does not have asynchronous notification (yet), and has different
needs/requirements for pacing. In short: the above paragraph
needs some discussion. This is tracked as PCP Issue #11 <xref
target="PCP-Issues"></xref>.]</t>
</list></t>
<t>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.</t>
</section>
<section title="Maintaining Pinholes">
<t>A PCP client can refresh a pinhole 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 pinholes, the Epoch value only needs to be retrieved for one
of them to verify the PCP server has not lost port forwarding
state.</t>
<t>If the client wishes to check the PCP server's Epoch, it sends a
PCP request for any one of the client's pinholes. 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).</t>
</section>
</section>
<section anchor="nested_nat" title="Nested NATs">
<t><list style="empty">
<t>[Ed. Note: Nested NATs will be discussed in a later version of
this document or, more likely, in a separate document. The
mechanism to support nested NATs is to have each NAT implement a
PCP server (to service devices and NATs behind it) and a PCP
client (to communicate with NATs above it). This allows a PCP
client to be unaware of the PCP communications going on between
upstream NATs.] This is tracked as PCP Issue #25 <xref
target="PCP-Issues"></xref>.]</t>
<t>[Ed. Note: In this document, we do need to describe how to
detect a non-PCP-aware NAT on the path, especially for
PEER4/PEER6, as it indicates the application cannot use the longer
lifetime for its keepalive traffic.]</t>
</list></t>
</section>
<section anchor="delete" title="Pinhole Deletion">
<t>A PCP Client can delete a pinhole immediately by sending the
appropriate PIN OpCode with a lifetime of 0. The PCP server responds
by returning a PIN Response with a lifetime of 0.</t>
<t>To delete all pinholes for all hosts associated with this
subscriber, an all-zero internal IP address is used.</t>
</section>
<section anchor="refresh" title="Pinhole Lifetime Extension">
<t>An existing mapping can have its lifetime extended by the PCP
client. To do this, the PCP client sends a new PCP map request to the
server indicating the internal IP address and port(s).</t>
<t>The PCP Client SHOULD renew the mapping before its expiry time,
otherwise it will be removed by the PCP Server (see <xref
target="pin-sec_server_delete"></xref>). In order to prevent excessive
PCP chatter, it is RECOMMENDED to renew only 60 seconds before
expiration time (to account for retransmissions that might be
necessary due to packet loss, clock synchronization between PCP client
and PCP server, and so on).</t>
</section>
</section>
<section anchor="peer_opcodes" title="PEER OpCodes">
<t>This section defines two OpCodes for controlling dynamic connections.
They are: <list hangIndent="8" style="hanging">
<t hangText="PEER4=4:">Set or query lifetime for flow from IPv4
address to a remote peer's IPv4 address.</t>
<t hangText="PEER6=5:">Set or query lifetime for flow from IPv6
address to a remote peer's IPv6 address.</t>
</list></t>
<t>The operation of these OpCodes is described in this section.</t>
<section title="OpCode Packet Formats">
<t>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.</t>
<t>The following diagram shows the request packet format for PEER4 and
PEER6. This packet format is aligned with the response packet
format:</t>
<figure align="center" anchor="peer_request"
title="PEER OpCode Request Packet Format">
<preamble></preamble>
<artwork><![CDATA[
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) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: Reserved (128 bits) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Requested lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| internal port | reserved (16 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| remote peer port | reserved (16 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
<t>These fields are described below:<list style="hanging">
<t hangText="Protocol:">indicates protocol associated with this
OpCode. Values are taken from the <xref
target="proto_numbers">IANA protocol registry</xref>. For example,
this field contains 6 (TCP) if the OpCode is describing a TCP
peer.</t>
<t hangText="External_AF:">The address family of the external IP
address associated with this peer connection.</t>
<t hangText="Reserved:">16 reserved bits, MUST be 0 on
transmission and MUST be ignored on reception.</t>
<t hangText="Pinhole 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).</t>
<t hangText="Remote Peer IP Address:">Remote peer's IP address,
from the perspective of the PCP client.</t>
<t hangText="Reserved:">128 reserved bits, MUST be 0 on
transmission and MUST be ignored on reception.</t>
<t hangText="internal port:">Internal port for the of the
5-tuple.</t>
<t hangText="Reserved:">16 reserved bits, MUST be 0 on
transmission and MUST be ignored on reception.</t>
<t hangText="Remote Peer Port:">Remote peer's port of the
5-tuple.</t>
<t hangText="Reserved:">16 reserved bits, MUST be 0 on
transmission and MUST be ignored on reception.</t>
</list><figure align="center" anchor="peer_response"
title="PEER OpCode Request Packet Format">
<preamble></preamble>
<artwork><![CDATA[
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 (32 bits if External_AF=IPv4, :
: 128 bits if External_AF=IPv6) :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Assigned lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| internal port | external port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| remote peer port | reserved (16 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure><list style="hanging">
<t hangText="Protocol:">Copied from the request.</t>
<t hangText="External_AF">Copied from the request</t>
<t hangText="Reserved:">16 reserved bits, MUST be 0 on
transmission, MUST be ignored on reception.</t>
<t hangText="Internal IP address">Copied from the request.</t>
<t hangText="remote Peer IP address">Copied from the request.</t>
<t hangText="External IP Address">External IP address, assigned by
the NAT (or firewall) to this pinhole. If firewall, this will
match the internal IP address.</t>
<t hangText="Assigned lifetime:">Assigned lifetime, in
seconds.</t>
<t hangText="internal port:">copied from request.</t>
<t hangText="external port:">External IP address, assigned by the
NAT (or firewall) to this pinhole. If firewall or 1:1 NAT, this
will match the internal port.</t>
<t hangText="remote peer port:">Copied from request.</t>
<t hangText="Reserved:">16 reserved bits, MUST be 0 on
transmission, MUST be ignored on reception.s</t>
</list></t>
</section>
<section anchor="peer-opcode-specific-result-codes"
title="OpCode-Specific Result Codes">
<t>In addition to the result codes described in <xref
target="figure_result_codes"></xref>, the following additional result
codes may be returned as a result of the two PEER OpCodes received by
the PCP server.</t>
<figure anchor="figure_peer_result_codes"
title="Result Codes specific to PEER OpCodes">
<artwork align="center"><![CDATA[
150 - UNSUPP_PROTOCOL, unsupported Protocol
]]></artwork>
</figure>
<t>Other OpCodes are in result codes are defined following the
procedure in <xref target="iana_result_codes"></xref>.</t>
</section>
<section anchor="peer_opcode_client_operation"
title="OpCode-Specific Client Operation, Processing a Response">
<t>This section describes the operation of a client when sending the
OpCodes PEER4 or PEER6.</t>
<t>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 pinhole
created by the OpCode.</t>
<t>If a successful response, the PCP client uses the assigned lifetime
value to reduce its frequency of application keepalives for the NAT.
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.</t>
<t>If an unsuccessful result code greater than or equal to 128, the
PCP client SHOULD NOT re-issue the same request. If a result code less
than or equal to 127, the PCP client MAY, if it wishes, resend the
same message after a delay of at least 5 seconds.</t>
</section>
<section anchor="peer-opcode_server_operation"
title="OpCode-Specific Server Operation">
<t>This section describes the operation of a client when processing
the OpCodes PEER4 or PEER6.</t>
<t>[Ed. Note: Add text]</t>
<t>The PCP server then validates that the internal IP address in the
PIN OpCode belongs to the same subscriber. This validation depends on
the PCP deployment scenario; see <xref
target="subscriber_identification"></xref> 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.</t>
<t>If all of the proceeding operations were successful (did not
generate an error response), then ...</t>
</section>
</section>
<section anchor="scenarios" title="Deployment Scenarios">
<section title="Dual Stack-Lite">
<t>The interesting components in a Dual-Stack Lite deployment are the
B4 element (which is the customer premise router) and the AFTR element
(which is the device that both terminates the IPv6-over-IPv4 tunnel
and also implements the large-scale 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.</t>
<section title="Overview">
<t>Various PCP deployment scenarios can be considered to control the
PCP server embedded in the AFTR element:<list style="numbers">
<t>UPnP IGD and 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 <xref
target="upnp-interworking"></xref>.</t>
<t>Hosts behind the B4 element with either include a PCP client
or UPnP IGD client.<list style="letters">
<t>if a UPnP IGD client, the B4 element will need to include
an interworking function from UPnP IGD to PCP.</t>
<t>if a PCP client, the PCP client will communicate directly
with the PCP server.</t>
</list></t>
<t>The B4 element include 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.</t>
</list></t>
<t>Two modes are identified to forward PCP packets to a PCP Server
controlling the provisioned AFTR as described in the following
sub-sections.</t>
<t><list style="empty">
<t>[Ed. Note: We need to decide on Encapsulation Mode or Plain
IPv6 Mode. This is tracked as PCP Issue #13 <xref
target="PCP-Issues"></xref>.]</t>
</list></t>
</section>
<section anchor="dslite_encap" title="Encapsulation Mode">
<t>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 AFTR decapsulates the IPv4 packets and processes
the PCP requests (because the destination IPv4 address points to the
PCP Server embedded in the AFTR).</t>
</section>
<section anchor="dslite_plain" title="Plain IPv6 Mode">
<t>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.</t>
</section>
</section>
<section title="NAT64">
<t>Hosts behind a NAT64 device can make use of PCP in order to perform
port reservation (to get a publicly routable IPv4 port).</t>
<t>If the IANA-assigned IP address is used for the discovery of the
PCP Server, that IPv4 address can be placed into the IPv6 destination
address following that particular network's well-known prefix or
network-specific prefix, per <xref target="RFC6052"></xref>.</t>
</section>
<section title="NAT44 and NAT444">
<t>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 large scale
NAT (LSN). 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".<list
style="empty">
<t>[Ed. Note: Does PCP need a mechanism to detect a
non-PCP-supporting NAT between a PCP client and a PCP server? Or
can that problem be detected by relying on the failure of PCP
Server Discovery? This is tracked as PCP Issue #25 <xref
target="PCP-Issues"></xref>.]</t>
</list></t>
</section>
<section title="IPv6 Firewall">
<t>See <xref target="remote_peer_filter"></xref>.<list style="empty">
<t>[Ed. Note: this IPv6 firewall section needs more text. This is
tracked as PCP Issue #10 <xref target="PCP-Issues"></xref>.]</t>
</list></t>
</section>
<section anchor="subscriber_identification"
title="Subscriber Identification">
<t>The PIN OpCodes require subscriber identification because they
allocate resources or adjust resources allocated to a subscriber. For
the PIN OpCode, it is permitted for a PCP Client to create a mapping
on behalf of a third party device (e.g., a computer can create PCP
mappings on behalf of a webcam). However, a PCP client cannot open
pinholes for a different subscriber. The mechanism to identify "same
subscriber" depends on the sort of NAT on this network:<list
style="symbols">
<t>If the PCP-controlled device is a NAT64: the internal IP
address indicated in the PCP message and the source IPv6 address
of received PCP request MUST belong to the same IPv6 prefix. The
length of the IPv6 prefix is the same as the length assigned to
each subscriber on that particular network (e.g., /64), and that
length must be configurable by the network operator.</t>
<t>If the PCP-controlled device is a DS-Lite AFTR: DS-Lite
(Section 11 of <xref
target="I-D.ietf-softwire-dual-stack-lite"></xref>) already
requires the tunnel transport source address be validated, and
that same address is used by PCP to assign the tunnel-ID to the
requested mapping (see <xref target="dslite_encap"></xref> and
<xref target="dslite_plain"></xref>). Thus, PCP acquires the same
security properties as DS-Lite. If address validation is
implemented correctly, the PCP Client can not instruct mappings on
behalf of devices of another subscriber.</t>
<t>If LSN with a routed network (NAT44), each subscriber has a
known set of IPv4 address (usually one IPv4 address) and all PCP
requests MUST be sent from only one of the subscriber's IP
addresses and MUST only open pinholes towards the subscriber's own
IP address.</t>
<t>If IPv6 firewall: the internal IP address indicated in the PCP
message and the source IPv6 address of received PCP request MUST
belong to the same IPv6 prefix. The length of the IPv6 prefix is
the same as the length assigned to each subscriber on that
particular network (e.g., /64), and that length must be
configurable by the network operator.</t>
</list></t>
<t>PCP-controlled devices can be a DS-Lite AFTR or an IPv4-IPv6
interconnection node such as NAT46 or NAT64. These nodes are deployed
by Service Providers to deliver global connectivity service to their
customers. Appropriate functions to restrict the use of these
resources (e.g., LSN facility) to only subscribed users should be
supported by these devices. Access control can be implicit or
explicit: <list style="symbols">
<t>It is said to be explicit if an authorisation procedure is
required for a user to be granted access to such resources. For
such variant of PCP-controlled device, a subscriber can be
identified by an IPv6 address, an IPv4 address, a MAC address, or
any other information.</t>
<t>For other scenarios, such as plain IPv4-in-IPv6 encapsulation
for a DS-Lite architecture, the access to the service is based on
the source IPv6 prefix. No per-user polices is pre-configured in
the PCP-controlled device.</t>
</list></t>
</section>
</section>
<section anchor="upnp-interworking"
title="Interworking with UPnP IGD 1.0 and 2.0">
<t><list style="empty">
<t>[Ed. Note: This UPnP IGD Interworking section will likely be
moved to a separate document which will fully describe how a proxy
needs to translate UPnP IGD messages into PCP messages. This is
tracked as PCP Issue #28 <xref target="PCP-Issues"></xref>.]</t>
</list></t>
<t>The following diagram shows how UPnP IGD can be interworked with PCP,
using an interworking function (IWF).</t>
<figure align="center" anchor="igd-interworking-function"
title="Network Diagram, Interworking UPnP IGD and PCP">
<artwork><![CDATA[
+-------------+
| IGD Control |
| Point |-----+
+-------------+ | +---------+ +--------+
+---| IGD-PCP | | PCP |
| IWF +-------+ Server |--<Internet>
+---| | | |
+-------------+ | +---------+ +--------+
| Local Host |-----+
+-------------+ | |
| |
LAN Side | WAN side |
<======UPnP IGD=============>|<========PCP=====>|
]]></artwork>
</figure>
<section title="UPnP IGD 1.0 with AddPortMapping Action">
<t>In <xref target="IGD">UPnP IGD 1.0</xref> it is only possible to
request a specific port using the AddPortMapping action. Requiring a
specific port is incompatible with both (1) a large-scale NAT and with
(2) widely-deployed applications. Regarding (1), another subscriber is
likely to already be using the same port, so it will be unavailable to
this application to operate a server. Regarding (2), if the same
popular application exists on two devices behind the same NAPT, they
cannot both get the same port. PCP cannot correct this behavior of
UPnP IGD:1, but PCP does work with this behavior.</t>
<t>Due to this incompatibility with large-scale address sharing and
popular applications, future hosts and applications will either
support UPnP IGD 2.0's AddAnyPortMapping method (see <xref
target="upnp-2-interworking"></xref>) or will support PCP.</t>
<t>When a requested port assignment fails, most UPnP IGD control
points will retry the port assignment requesting the next higher port
or requesting a random port. These UPnP IGD requests are translated to
PCP requests and sent to the PCP server. The requests include the
HONOR_EXTERNAL_PORT option, which causes the PCP server to return an
error if it cannot allocate the requested port. The interworking
function translates the PCP error response to a UPnP IGD error
response. This repeats until the UPnP IGD client gives up or until the
PCP server is able to return the requested port.</t>
<figure align="left" anchor="message-flow-upnp-1"
title="Message Flow: Interworking from UPnP IGD 1.0 AddPortMapping action to PCP">
<preamble>Message flow would be similar to this:</preamble>
<artwork align="center"><![CDATA[
UPnP Control Point in-home CPE PCP server
| | |
|-UPnP:AddPortMapping(80)--->| |
| |-PCP:request port 80------>|
| | HONOR_EXTERNAL_PORT |
| | |
| |<-PCP:error----------------|
|<-UPnP: unavailable---------| |
| | |
|-UPnP:AddPortMapping(3213)->| |
| |-PCP:request port 3213---->|
| | HONOR_EXTERNAL_PORT |
| | |
| |<-PCP:error----------------|
|<-UPnP: unavailable---------| |
| | |
... ... ... ...
| | |
|-UPnP:AddPortMapping(8921)->| |
| |-PCP:request port 8921---->|
| | HONOR_EXTERNAL_PORT |
| | |
| |<-PCP:ok, port 8921--------|
|<-UPnP: ok, port 8921-------| |
| | |
]]></artwork>
</figure>
</section>
<section anchor="upnp-2-interworking"
title="UPnP IGD 2.0 with AddAnyPortMapping Action">
<t>If the UPnP IGD control point and the UPnP IGD interworking
function both implement <xref target="IGD-2">UPnP IGD 2.0</xref> and
the UPnP IGD control point uses IGD 2's new AddAnyPortMapping action,
only one round-trip is necessary. This is because AddAnyPortMapping
has semantics similar to PCP's semantics, allowing the PCP server to
assign any port.</t>
<figure align="left" anchor="message-flow-upnp-2"
title="Message Flow: Interworking from UPnP IGD 2.0 AddAnyPortMapping action to PCP">
<preamble>Message flow would be similar to this:</preamble>
<artwork align="center"><![CDATA[
UPnP Control Point in-home CPE PCP server
| | |
|-UPnP:AddAnyPortMapping()->| |
| |-PCP:external port 0----->|
| |<-PCP:external port=12345-|
|<-UPnP:port=12345----------| |
| | |
]]></artwork>
</figure>
</section>
<section title="Lifetime Maintenance">
<t>Neither UPnP IGD 1.0 nor 2.0 provide a lifetime. Thus, the UPnP
IGD/PCP interworking function is responsible for extending the
lifetime of mappings that are still interesting to the UPnP IGD
control point.</t>
<t><list style="empty">
<t>Note: It can be an implementation advantage, where possible,
for the UPnP IGD/PCP interworking function to request a port
mapping lifetime only while that client is active and connected.
For example, creating a PCP mapping that is equal to the client's
remaining DHCP lifetime is one useful approach. The UPnP IGD/PCP
interworking function is responsible for renewing the PCP lifetime
as necessary. For clients not using DHCP, other mechanisms to
check on the client host's liveliness can also be useful (e.g.,
ping, ARP, or WiFi association) can be used to discern liveliness
of the UPnP IGD control point. However, it is NOT RECOMMENDED to
attempt to connect to the TCP or UDP port opened on the control
point to determine if the host still wants to receive packets, as
the server could be temporarily down when tested, causing a false
negative.</t>
</list></t>
</section>
</section>
<section anchor="security" title="Security Considerations">
<t>[Ed. Note: The following recommendation does not have consensus] The
PCP Client SHOULD be bound to one single UDP port which SHOULD be
randomly generated as per <xref
target="I-D.ietf-tsvwg-port-randomization"></xref>.</t>
<t>On today's Internet, ISPs to not typically filter incoming traffic
for their subscribers. However, when ISP introduce stateful address
sharing with NAPT devices, such filtering will occur as a side effect.
PCP allows controlling that filtering, and PCP allows indicating the
'inside' IP address that should have the filtering removed. It is
important that PCP allow removing the filtering for hosts belonging to
one subscriber, but not hosts belonging to another subscriber. This is
done in different ways depending on the architecture of the address
sharing device and how subscribers are identified behind that device,
and described in detail in <xref
target="subscriber_identification"></xref>.</t>
<t>Because of the state created in a NAPT or firewall, it is
anticipated that port forwarding (PIN OpCodes) will have a quota
applied to each subscriber. If the quota is small and the maximum
lifetime is large, a faulty or disconnected PCP client could cause a
denial of service for other PCP clients belonging to that same
subscriber. To prevent this problem, if a PCP server is configured for a
small per-subscriber quota (e.g., less than 15 ports) then it is
RECOMMENDED it also be be configured for a short maximum lifetime
(e.g., 5 minutes).</t>
</section>
<section anchor="iana" title="IANA Considerations">
<t>IANA is requested to perform the following actions:</t>
<section title="PCP Server IP address">
<t>IANA shall assign an IPv4 and an IPv6 address for PCP
discovery.</t>
<t>[Ed. Note: perhaps we can use the AFTR element's IPv4 address? But
still need an IPv6 address assigned for PIN64 and PIN66. This is
tracked as PCP Issue #8 <xref target="PCP-Issues"></xref>.]</t>
</section>
<section anchor="iana_port" title="Port Number">
<t>IANA has assigned UDP port 44323 for PCP.</t>
</section>
<section anchor="iana_opcodes" title="OpCodes">
<t>IANA shall create a new protocol registry for PCP OpCodes,
initially populated with the values in <xref
target="pin_opcodes"></xref> and <xref
target="peer_opcodes"></xref>.</t>
<t>New OpCodes in the range 1-95 can be created via <xref
target="RFC5226">Standards Action</xref>, and the range 96-128 is for
<xref target="RFC5226">Private Use</xref>.</t>
</section>
<section anchor="iana_result_codes" title="Result Codes">
<t>IANA shall create a new registry for PCP result codes, numbered
0-255, initially populated with the result codes from both <xref
target="figure_result_codes"></xref> and <xref
target="figure_pin_result_codes"></xref>.</t>
<t>New Result Codes can be created via <xref
target="RFC5226">Specification Required</xref>.</t>
</section>
<section anchor="iana_ie" title="Options">
<t>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 <xref target="pin_options"></xref>, and the
option values 0 and 255 are reserved.</t>
<t>New information elements in the range 0-63 and 128-192 can be
created via <xref target="RFC5226">Standards Action</xref>, and the
range 64-127 and 192-255 is for <xref target="RFC5226">Private
Use</xref>.</t>
</section>
</section>
<section title="Authors">
<figure>
<preamble>The following individuals contributed substantial text to
this document and are listed in alphabetical order:</preamble>
<artwork><![CDATA[ Mohamed Boucadair
France Telecom
Email: mohamed.boucadair@orange-ftgroup.com
Stuart Cheshire
Apple Inc.
1 Infinite Loop
Cupertino, California 95014 USA
Phone: +1 408 974 3207
EMail: cheshire@apple.com
Francis Dupont
ISC
Email: Francis.Dupont@fdupont.fr
Reinaldo Penno
Juniper Networks
Email: rpenno@juniper.net
]]></artwork>
<postamble></postamble>
</figure>
</section>
<section title="Acknowledgments">
<t>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 pinholes.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<?rfc include="reference.RFC.5226"?>
<?rfc include="reference.RFC.6052"?>
<?rfc include='reference.I-D.ietf-softwire-dual-stack-lite'?>
<?rfc include='reference.I-D.ietf-behave-v6v4-xlate'?>
<?rfc include='reference.I-D.ietf-behave-v6v4-xlate-stateful'?>
<?rfc include='reference.RFC.4193'?>
<?rfc include='reference.I-D.ietf-tsvwg-port-randomization'?>
<reference anchor="proto_numbers"
target="http://www.iana.org/assignments/protocol-numbers/protocol-numbers.xml">
<front>
<title>Protocol Numbers</title>
<author fullname="IANA" surname="IANA">
<organization></organization>
</author>
<date year="2010" />
</front>
</reference>
</references>
<references title="Informative References">
<?rfc include='reference.RFC.2608'?>
<?rfc include='reference.RFC.4961'?>
<?rfc include='reference.RFC.3581'?>
<?rfc include='reference.RFC.5461'?>
<?rfc include='reference.RFC.3424'?>
<?rfc include='reference.RFC.0793'?>
<?rfc include='reference.I-D.miles-behave-l2nat'?>
<?rfc include='reference.I-D.ietf-v6ops-cpe-simple-security'?>
<?rfc include='reference.I-D.ietf-behave-lsn-requirements'?>
<?rfc include='reference.I-D.arkko-dual-stack-extra-lite'?>
<reference anchor="IGD"
target="http://upnp.org/specs/gw/UPnP-gw-WANIPConnection-v1-Service.pdf">
<front>
<title>WANIPConnection:1</title>
<author fullname="UPnP Gateway Committee"
surname="UPnP Gateway Committee">
<organization>UPnP Forum</organization>
</author>
<date month="November" year="2001" />
</front>
</reference>
<reference anchor="IGD-2" target="http://upnp.org/specs/gw/igd2">
<front>
<title>Internet Gateway Device (IGD) V 2.0</title>
<author fullname="UPnP Gateway Committee"
surname="UPnP Gateway Committee">
<organization>UPnP Forum</organization>
</author>
<date month="September" year="2010" />
</front>
</reference>
<reference anchor="PCP-Issues"
target="http://trac.tools.ietf.org/wg/pcp/trac/report/1">
<front>
<title>PCP Active Tickets</title>
<author fullname="PCP Working Group" surname="PCP Working Group">
<organization>IETF</organization>
</author>
<date month="January" year="2011" />
</front>
</reference>
<!--
<reference anchor="Saltzer84"
target="http://web.mit.edu/Saltzer/www/publications/endtoend/endtoend.pdf">
<front>
<title>End-to-end arguments in system design</title>
<author initials="J.H." surname="Saltzer">
<organization></organization>
</author>
<author initials="D.P." surname="Reed">
<organization></organization>
</author>
<author initials="D.D." surname="Clark">
<organization></organization>
</author>
<date year="1984" />
</front>
</reference>
-->
</references>
<section title="Changes">
<section title="Changes from draft-ietf-pcp-base-02 to -03">
<t><list style="symbols">
<t>Adjusted abstract and introduction to make it clear PCP is intended
to forward ports and intended to reduce application keepalives.</t>
<t>First bit in PCP common header is set. This allows DTLS and
non-DTLS to be multiplexed on same port, should we want to add
DTLS support.</t>
<t>Moved subscriber identity from common PCP section to PIN*
section.</t>
<t>made clearer that PCP client can reduce mapping lifetime if it
wishes.</t>
<t>Added discussion of host running a server, client, or symmetric
client+server.</t>
<t>Introduced PEER4 and PEER6 OpCodes.</t>
<t>Removed REMOTE_PEER Option, as its function has been replaced
by the new PEER OpCodes.</t>
<t>IANA assigned port 44323 to PCP.</t>
<t>Removed AMBIGUOUS error code, which is no longer needed.</t>
</list></t>
</section>
<section title="Changes from draft-ietf-pcp-base-01 to -02">
<t><list style="symbols">
<t>more error codes</t>
<t>PCP client source port number should be random</t>
<t>PCP message minimum 8 octets, maximum 1024 octets.</t>
<t>tweaked a lot of text in section 7.4, "Opcode-Specific Server
Operation".</t>
<t>opening a pinhole also allows ICMP messages associated with
that pinhole.</t>
<t>HONOR_EXTERNAL_PORT value changed to the mandatory-to-process
range.</t>
<t>added text recommending applications that are crashing obtain
short lifetimes, to avoid consuming subscriber's port quota.</t>
</list></t>
</section>
<section title="Changes from draft-ietf-pcp-base-00 to -01">
<t><list style="symbols">
<t>Significant document reorganization, primarily to split base
PCP operation from OpCode operation.</t>
<t>packet format changed to move 'protocol' outside of PCP common
header and into the PIN* opcodes</t>
<t>Renamed Informational Elements (IE) to Options.</t>
<t>Added REMOTE_PEER (for disambiguation with dynamic ports),
REMOTE_PEER_FILTER (for simple packet filtering), and
HONOR_EXTERNAL_PORT (to optimize UPnP IGD interworking)
options.</t>
<t>Is NAT or router behind B4 in scope?</t>
<t>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.</t>
<t>Response code most significant bit now indicates
permanent/temporary error</t>
<t>PCP Options are split into mandatory-to-process ("P" bit), and
into Specification Required and Private Use.</t>
<t>Epoch discussion simplified.</t>
</list></t>
</section>
</section>
<section anchor="discovery_analysis"
title="Analysis of Techniques to Discover PCP Server">
<t><list style="empty">
<t>[Ed. Note: This Appendix will be removed in a later version of
this document. It is included here for reference and discussion
purposes. This is tracked as PCP Issue #8 <xref
target="PCP-Issues"></xref>.]</t>
</list></t>
<t><list style="empty">
<t>Discussion Note: A deployment model is a non-PCP aware NAT in a
home, and a PCP-aware large scale NAT (LSN) operated by the ISP. For
example, the home users purchased a NAT last year at a computer shop
(to extend their home's WiFi network). This could work by having the
host use UPnP IGD with the in-home NAT, and the host use PCP with
the LSN. But this deployment model is impossible with several of the
mechanisms below. Is this deployment model important, or can we wait
for PCP to be enabled on CPE?</t>
</list></t>
<t>Several mechanisms for discovering the PCP Server can be envisaged as
listed below:</t>
<t><list style="numbers">
<t>A special-purpose IPv4 or IPv6 address, assigned by IANA, which
is routed normally until it hits a PCP Server, which responds. <list
style="empty">
<t>Analysis: This solution can be deployed in the context of
DS-Lite architecture. Concretely, a well-known IPv4 address can
be used to reach a PCP Server embedded in the device that embeds
the AFTR capabilities. Since all IPv4 messages issued by a
DS-Lite CP router will be encapsulated in IPv6, no state
synchronisation issues will be experienced because PCP messages
will be handled by the appropriate PCP Server.</t>
<t>In some deployment scenarios (e.g., deployment of several
stateful NAT64/NAT46 in the same domain), the use of this
address is not recommended since PCP messages, issued by a given
host, may be handled by a PCP Server embedded in a NAT node
which is not involved to handle IP packets issued from that
host. The use of this special-purpose IP address may induce
session failures and therefore the customer may experience
troubles when accessing its services.</t>
<t>Consequently, the use of a special-purpose IPv4 address is
suitable for DS-Lite NAT44. As for NAT46/NAT64, this is left to
the Service Providers according to their deployment
configuration.</t>
<t>The special-use address MUST NOT be advertised in the global
routing table. Packets with that destination address SHOULD be
filtered so they are not transmitted on the Internet.</t>
</list></t>
<t>Assume the default router is a PCP Server, and send PCP packets
to the IP address of the default router. <list style="empty">
<t>Analysis: This solution is not suitable for DS-Lite NAT44 nor
for all variants of NAT64/NAT46. <list style="empty">
<t>In the context of DS-Lite: There is no default IPv4
router configured in the CP router. All outgoing IPv4
traffic is encapsulated in IPv6 and then forwarded to a
pre-configured DS-Lite AFTR device. Furthermore, if IPv6 is
used to reach the PCP Server, the first router may not be
the one which embeds the AFTR.</t>
<t>For NAT64/NAT46 scenarios: The NAT function is not
embedded in the first router, therefore this solution
candidate does not allow to discover a valid PCP Server.</t>
</list></t>
<t>Therefore, this alternative is not recommended.</t>
</list></t>
<t>Service Location Protocol (<xref
target="RFC2608">SLP</xref>).<list style="empty">
<t>Analysis: This solution is not suitable in scenarios where
multicast is not enabled. SLP is a chatty protocol. This
alternative is not recommended.</t>
</list></t>
<t>NAPTR. The host would issue a DNS query for a NAPTR record,
formed from some bits of the host's IPv4 or IPv6 address. For
example, a host with the IPv6 address 2001:db8:1:2:3:4:567:89ab
would first send an NAPTR query for
3.0.0.0.2.0.0.0.1.0.0.0.8.b.d.0.1.0.0.2.IP6.ARPA (20 elements,
representing a /64 network prefix), which returns the PCP Server's
IPv6 address. A similar scheme can be used with IPv4 using, for
example, the first 24 bits of the IPv4 address.<list style="empty">
<t>Analysis: This solution candidate requires more configuration
effort by the Service Provider so as to redirect a given client
to the appropriate PCP Server. Any change of the engineering
policies (e.g., introduce new LSN device, load-based
dimensioning, load-balancing, etc.) would require to update the
zone configuration. This would be a hurdle for the flexibility
of the operational networks. Adherence to DNS is not encouraged
and means which allows for more flexibility are to be
promoted.</t>
<t>Therefore, this mechanism is not recommended.</t>
</list></t>
<t>New DHCPv6/DHCP option and/or a RA option to convey an FQDN of a
PCP Server.<list style="empty">
<t>Analysis: Since DS-Lite and NAT64/NAT46 are likely to be
deployed in provider-provisioned environments, DHCP (both DHCPv6
and IPv4 DHCP) is convenient to provision the address/FQDN of
the PCP Server.</t>
</list></t>
</list></t>
</section>
</back>
</rfc>
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