PCP Working Group F. Dupont
Internet-Draft Internet Systems Consortium
Intended status: Standards Track T. Tsou
Expires: May 2, 2012 Huawei Technologies
J. Qin
ZTE Corporation
October 30, 2011
The Port Control Protocol in Dual-Stack Lite environments
draft-dupont-pcp-dslite-01
Abstract
This document specifies the so-called "plain mode" for the use of the
Port Control Protocol (PCP) in Dual-Stack Lite (DS-Lite)
environments.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 2, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
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described in the Simplified BSD License.
1. Introduction
The Dual-Stack Lite (DS-Lite, [RFC6333]) is a technology which
enables a broadband service provider to share IPv4 addresses among
customers by combining two well-known technologies: IP in IP (IPv4-
in-IPv6) and Network Address Translation (NAT).
Typically, the home gateway embeds a Basic Bridging BroadBand (B4)
capability that encapsulates IPv4 traffic into a IPv6 tunnel to the
carrier-grade NAT, named the Address Family Transition Router (AFTR).
AFTRs are run by service providers.
The Port Control Protocol (PCP, [I-D.ietf-pcp-base] allows customer
applications to create mappings in a NAT for new inbound
communications destined to machines located behind a NAT. In a DS-
Lite environment, PCP servers control AFTR devices.
Two different modes of operations were proposed: the plain and the
encapsulation modes. This document selects the plain mode as the one
to use.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Plain Mode
In the plain mode the B4, the customer end-point of the DS-Lite IPv6
tunnel, implements a PCP proxy ([I-D.bpw-pcp-proxy]) function and
uses UDP over IPv6 with the AFTR to send PCP requests and receive PCP
responses.
The B4 MUST source PCP requests with the IPv6 address of its DS-Lite
tunnel end-point and MUST use a THIRD PARTY option either empty or
carrying the IPv4 internal address of the mappings.
In the plain mode the PCP discovery ([I-D.ietf-pcp-base] section 7.1
"General PCP Client: Generating a Request") is changed into:
1. if a PCP server is configured (e.g., in a configuration file or
via DHCPv6), that single configuration source is used as the list
of PCP Server(s), else;
2. use the IPv6 address of the AFTR.
To summary: the first rule remains the same with the precision that
DHCP is DHCPv6, in the second rule the default router list is
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replaced by the AFTR.
3. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
4. Security Considerations
The plain mode provides a control point inside the home network where
any policy on PCP requests can be applied, e.g.:
o restrict the use of THIRD PARTY options to the B4
o apply an access-list on internal addresses and/or ports
At the opposite the encapsulation mode Appendix A by default is fully
transparent for the B4: PCP requests are blindly encapsulated as any
other IPv4 packets to the Internet. So to apply a policy on them
requires heavier and far less flexible tools.
5. Acknowledgments
Reinaldo Penno who checks the validity of the argument about the
relative complexity of the encapsulation mode at the AFTR side.
Christian Jacquenet and Mohammed Boucadair who proposed improvements
to the document, including the PCP server discovery by Mohammed.
6. References
6.1. 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-16 (work in progress), October 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, August 2011.
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6.2. Informative References
[I-D.bpw-pcp-proxy]
Boucadair, M., Penno, R., Wing, D., and F. Dupont, "Port
Control Protocol (PCP) Proxy Function",
draft-bpw-pcp-proxy-02 (work in progress), September 2011.
[I-D.bpw-pcp-upnp-igd-interworking]
Boucadair, M., Penno, R., Wing, D., and F. Dupont,
"Universal Plug and Play (UPnP) Internet Gateway Device
(IGD)-Port Control Protocol (PCP) Interworking Function",
draft-bpw-pcp-upnp-igd-interworking-02 (work in progress),
February 2011.
Appendix A. Encapsulation Mode
The encapsulation mode deals at the B4 side with PCP traffic as any
IPv4 traffic: it is encapsulated to and decapsulated from the AFTR
over the DS-Lite IPv4 over IPv6 tunnel.
At the AFTR side things are a bit more complex because the PCP server
needs the context, here the source IPv6 address, for both to manage
mappings and to send back response. So the AFTR MUST tag PCP
requests with the source IPv6 address after decapsulation and before
forwarding them to the PCP server, and use the same tag to
encapsulate PCP responses to correct B4s. (the term "tag" is used to
describe the private convention between the AFTR and the PCP server).
Appendix B. Justification
We believe most customers will run a PCP proxy on the B4 because:
o they want a control point where to apply security (Section 4)
o they run an InterWorking Function (IWF) for other protocols
([I-D.bpw-pcp-upnp-igd-interworking]) on the B4 so the proxy is
just part of a bigger system
BTW when the home network has only one node (dual-stack capable with
embedded B4 element) attached, it is the PCP client.
For a PCP proxy to use IPv4 (encapsulation mode) or IPv6 (plain mode)
does not make a sensible difference, so from an implementation point
of view the real difference is on the PCP server / AFTR side: the
encapsulation mode require an Application Level Gateway (ALG) to tag
PCP request with the corresponding customer after decapsulation, when
the plain mode is fully transparent.
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Authors' Addresses
Francis Dupont
Internet Systems Consortium
Email: fdupont@isc.org
Tina Tsou
Huawei Technologies
2330 Central Expressway
Santa Clara
USA
Phone: +1-408-330-4424
Email: tina.tsou.zouting@huawei.com
Jacni Qin
ZTE Corporation
Shanghai
P.R.China
Email: jacni@jacni.com
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