PCP Working Group M. Boucadair
Internet-Draft France Telecom
Intended status: Standards Track February 12, 2013
Expires: August 16, 2013
Learn NAT64 PREFIX64s using PCP
draft-ietf-pcp-nat64-prefix64-00
Abstract
This document defines a new PCP extension to learn the IPv6
prefix(es) used by a PCP-controlled NAT64 device to build IPv4-
embedded IPv6 addresses. This extension is needed for successful
communications when IPv4 addresses are used in referrals.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . . 3
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Issues . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.2.1. AAAA Synthesis by Stub-resolver . . . . . . . . . . . . 3
3.2.2. Applications Referrals . . . . . . . . . . . . . . . . 4
3.3. Illustration Example . . . . . . . . . . . . . . . . . . . 4
4. PREFIX64 Option . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Format . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Flow Example . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
This document defines a new PCP extension [I-D.ietf-pcp-base] to
inform PCP Clients about the Pref64::/n [RFC6052] used by a PCP-
controlled NAT64 device [RFC6146].
This extension is required to help establishing communications
between IPv6-only hosts and remote IPv4-only hosts.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Problem Statement
3.1. Issues
This document proposes a deterministic solution to solve the
following issues:
o Learn the Pref64::/n used by an upstream NAT64 function. This is
needed to help:
* distinguishing between IPv4-converted IPv6 addresses and native
IPv6 addresses.
* implementing IPv6 address synthesis for applications not
relying on DNS.
o Avoid stale Pref64::/n.
o Discover multiple Pref64::/n when multiple prefixes in a network.
o Use DNSSEC in the presence of NAT64.
Section 3.2 lists some applications which encounter the issues listed
above.
3.2. Use Cases
3.2.1. AAAA Synthesis by Stub-resolver
The extension defined in this document can be used for hosts with
DNS64 capability [RFC6147], added to the host's stub-resolver.
The stub resolver on the host will try to obtain (native) AAAA
records and if it they are not found, the DNS64 function on the host
will query for A records and then synthesizes AAAA records. Using
the PREFIX64 PCP extension, the host's stub-resolver can learn the
prefix used for IPv6/IPv4 translator and synthesize AAAA records
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accordingly.
Learning the Pref64::/n used to construct IPv4-converted IPv6
addresses [RFC6052] allows to make use of DNSSEC.
3.2.2. Applications Referrals
This PCP extension can be used by applications making use of address
referrals.
As Peer-to-Peer (P2P) communications for real-time communication is
becoming popular with RTCWEB (e.g., P2P for Media, data channels for
file transfer etc), this extension can be used to help for NAT64
traversal. SIP [RFC3261] is only one example among those protocols.
3.3. Illustration Example
An illustration example is shown in Figure 1. In this example, NAT64
is co-located with a PCP server while IPv6-only SIP UA interacts with
a PCP Client.
In Figure 1, the PCP Client issues a PCP MAP request with
PORT_RESERVATION_OPTION to reserve a pair of ports preserving parity
and contiguity [I-D.boucadair-pcp-rtp-rtcp]. A pair of ports and an
external IPv4 address are then returned by the PCP server to the
requesting PCP Client. This information is used by the IPv6-only SIP
UA to build its SDP offer which contains exclusively IPv4 addresses
(especially in the "c=" line, the port indicated for media port is
the external port assigned by the PCP server). The INVITE request
including the SDP offer is then forwarded by the NAT64 to the Proxy
Server which will relay it to the called party (i.e., IPv4-only SIP
UA) (Steps (1) to (3)). IPv4-only SIP UA accepts the offer and sends
back its SDP answer in a "200 OK" message which is relayed by the SIP
Proxy Server and NAT64 until being delivered to IPv6-only SIP UA
(Steps (4) to (6)).
At the end of this process, IPv4-only SIP UA can send media streams
to the IPv4 address/port as indicated in the SDP offer while IPv6-
only SIP UA can not send media streams as only IPv4 addresses are
present in the SDP answer.
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+---------+ +-----+ +------------+ +---------+
|IPv6-only| |NAT64| | IPv4 SIP | |IPv4-only|
| SIP UA | | | |Proxy Server| | SIP UA |
+---------+ +-----+ +------------+ +---------+
| (a) PCP MAP REQUEST | | |
|PORT_RESERVATION_OPTION| | |
|======================>| | |
| (b) PCP MAP RESPONSE | | |
|PORT_RESERVATION_OPTION| | |
|<======================| | |
| | | |
| (1) SIP INVITE | (2) SIP INVITE | (3) SIP INVITE |
|======================>|===============>|================>|
| (6) SIP 200 OK | (5) SIP 200 OK | (4) SIP 200 OK |
|<======================|<===============|<================|
| | | |
Figure 1
4. PREFIX64 Option
4.1. Format
The format of PREFIX64 PCP Option is depicted in Figure 2.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix64 (Variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Prefix64 PCP Option
The description of the fields is as follows:
o Option Code: To be assigned by IANA.
o Option Length: Indicates in octets the length of the Pref64::/n.
Allowed values are 4, 5, 6, 7, 8, or 12 [RFC6052].
o Prefix64: This field identifies the IPv6 unicast prefix to be used
for constructing an IPv4-embedded IPv6 address from an IPv4
address. The address synthesize MUST follow the guidelines
documented in [RFC6052].
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Option Name: PREFIX64
Number: To be assigned by IANA.
Purpose: Learn the prefix used by the NAT64 to build
IPv4-embedded IPv6 addresses. This is be used by a host
for local address synthesis (e.g., when IPv4 address is
present in referrals).
Valid for Opcodes: MAP
Length: Variable
May appear in: request, response.
Maximum occurrences: 1
4.2. Behaviour
A PCP Client MAY include a PREFIX64 PCP Option in a MAP request to
learn the IPv6 prefix used by an upstream PCP-controlled NAT64
device. When enclosed in a MAP request, PREFIX64 MUST be set to
::/96. PREFIX64 PCP Option can be inserted in a MAP request used to
learn the external IP address as detailed in Section 11.6 of
[I-D.ietf-pcp-base].
A PCP Server controlling a NAT64 SHOULD be configured to return to
requesting PCP Clients the value of the Pref64::/n used to build
IPv4-embedded IPv6 addresses. When enabled, PREFIX64 PCP Option
conveys the value of Pref64::/n.
A PCP Server controlling a NAT64 MAY be configured to inject a
PREFIX64 PCP Option in all MAP responses even if the option is not
listed in the associated request.
Upon receipt of the PREFIX64 PCP Option, the host embedding the PCP
Client uses Pref64::/n for local address synthesize [RFC6052]. How
the content of PREFIX64 PCP Option is passed to the OS is
implementation-specific.
A PCP Client SHOULD associate each received Pref64::/n with the PCP
Server from which the Pref64::/n information was retrieved.
5. Flow Example
Figure 3 shows an example of the use of the option defined in
Section 4.
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+---------+ +-----+ +------------+ +---------+
|IPv6-only| |NAT64| | IPv4 SIP | |IPv4-only|
| SIP UA | | | |Proxy Server| | SIP UA |
+---------+ +-----+ +------------+ +---------+
| (a) PCP MAP REQUEST | | |
|PORT_RESERVATION_OPTION| | |
| PREFIX64_OPTION | | |
|======================>| | |
| (b) PCP MAP RESPONSE | | |
|PORT_RESERVATION_OPTION| | |
| PREFIX64_OPTION | | |
|<======================| | |
| (1) SIP INVITE | (2) SIP INVITE | (3) SIP INVITE |
|======================>|===============>|================>|
| (6) SIP 200 OK | (5) SIP 200 OK | (4) SIP 200 OK |
|<======================|<===============|<================|
| (7) SIP ACK | (8) SIP ACK | (9) SIP ACK |
|======================>|===============>|================>|
| | | |
|<======IPv6 RTP=======>|<============IPv4 RTP============>|
|<===== IPv6 RTCP======>|<============IPv4 RTCP===========>|
| | |
Figure 3: Example of IPv6 to IPv4 SIP initiated Session
In Steps (a) and (b), the IPv6-only SIP UA retrieves a pair of ports
to be used for RTP/RTCP, the external IPv4 address and the Pref64::/n
to be used to build IPv4-embedded IPv6 addresses. The retrieved IPv4
address and port numbers are used to build the SDP offer in Step (1)
while Pref64::/n is used to construct a corresponding IPv6 address of
the IPv4 address enclosed in the SDP answer made by the IPv4-only SIP
UA (Step 6). RTP/RTCP flows are exchanged between an IPv6-only SIP
UA and an IPv4-only UA without requiring any ALG at the NAT64 and no
particular function to be supported by the IPv4-only SIP Proxy Server
to help establishing the session (e.g., Hosted NAT traversal).
When the session is initiated from IPv4 SIP UA (see Figure 4): Steps
(a) and (b), the IPv6-only SIP UA retrieves a pair of ports to be
used for RTP/RTCP, the external IPv4 address and the Pref64::/n to be
used to build IPv4-embedded IPv6 addresses. These two steps can be
delayed until receiving the INVITE message (Step 3).
The retrieved IPv4 address and port numbers are used to build the SDP
answer in Step (4) while Pref64::/n is used to construct a
corresponding IPv6 address of the IPv4 address enclosed in the SDP
offer made by the IPv4-only SIP UA (Step 3). RTP/RTCP flows are
exchanged between an IPv6-only SIP UA and an IPv4-only UA without
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requiring any ALG at the NAT64 and no particular function to be
supported by the IPv4-only SIP Proxy Server to help establishing the
session (e.g., Hosted NAT traversal).
+---------+ +-----+ +------------+ +---------+
|IPv6-only| |NAT64| | IPv4 SIP | |IPv4-only|
| SIP UA | | | |Proxy Server| | SIP UA |
+---------+ +-----+ +------------+ +---------+
| (a) PCP MAP REQUEST | | |
|PORT_RESERVATION_OPTION| | |
| PREFIX64_OPTION | | |
|======================>| | |
| (b) PCP MAP RESPONSE | | |
|PORT_RESERVATION_OPTION| | |
| PREFIX64_OPTION = | | |
| 2001:db8:122::/48 | | |
|<======================| | |
| (3) SIP INVITE | (2) SIP INVITE | (1) SIP INVITE |
|<======================|<===============|<================|
| (4) SIP 200 OK | (5) SIP 200 OK | (6) SIP 200 OK |
|======================>|===============>|================>|
| (9) SIP ACK | (8) SIP ACK | (7) SIP ACK |
|<======================|<===============|<================|
| | | |
|<======IPv6 RTP=======>|<============IPv4 RTP============>|
|<===== IPv6 RTCP======>|<============IPv4 RTCP===========>|
| | |
Figure 4: Example of IPv4 to IPv6 SIP initiated Session
6. IANA Considerations
This document requests a new PCP option:
PREFIX64
7. Security Considerations
This document does not introduce any security issue in addition to
what is taken into account in [I-D.ietf-pcp-base].
8. Acknowledgements
Many thanks to S. Perreault , R. Tirumaleswar, T. Tsou, D. Wing, J.
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Zhao and R. Penno for the comments and suggestions.
9. References
9.1. Normative References
[I-D.ietf-pcp-base]
Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)",
draft-ietf-pcp-base-29 (work in progress), November 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
October 2010.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
April 2011.
9.2. Informative References
[I-D.boucadair-pcp-rtp-rtcp]
Boucadair, M. and S. Sivakumar, "Reserving N and N+1 Ports
with PCP", draft-boucadair-pcp-rtp-rtcp-05 (work in
progress), October 2012.
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Author's Address
Mohamed Boucadair
France Telecom
Rennes, 35000
France
Email: mohamed.boucadair@orange.com
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