Network Working Group Jie Hu
Internet Draft Yunqing Chen
Intended status: Informational Huiling Zhao
Expires: April 18, 2011 Dongfeng Mao
China Telecom
October 18, 2010
PPPv6 Problem statement and requirements
draft-hu-pppext-ipv6cp-requirements-00
Abstract
The IPv6 Control Protocol (IPv6CP) is a NCP that allows for the
negotiation of parameters for an IPv6 interface over PPP. In IPv6
networks, PPP (PPPoE) will still be an important mechanism for
connecting broadband access users. However, IPv6CP only defines the
Interface-Identifier option, other parameters such as IPv6 Address,
Primary and alternative DNS server addresses, and delegated prefix
have to be configured by other methods rather than IPv6CP.
This document describes problems the ISPs faced and lists
requirements related when deploying IPv6 in broadband access network
over PPP.
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 April 18,2011.
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Table of Contents
1. Introduction ................................................................. 2
1.1. Requirements Language................................... 2
2. Current Practice in IPv4............................................. 3
3. Problem Statement ................................................... 3
4. Requirements ............................................................ 4
5. Security Considerations............................................ 5
6. Acknowledgments ..................................................... 5
7. References ................................................................. 5
7.1. Normative References........................................ 5
7.2. Informative References....................................... 5
Authors' address..............................................................6
1. Introduction
The Point-to-Point Protocol (PPP) provides a standard method for
transporting multi-protocol datagrams over point-to-point links. PPP
defines an extensible Link Control Protocol (LCP) and a family of
Network Control Protocols (NCPs) for establishing and configuring
different network-layer protocols.
In current practice, after the LCP and the authentication (if
required) phases are completed, the corresponding network-layer
control protocol, IPCP will be used to negotiate IP layer elements
between subscriber devices and the BNGs.
1.1. Requirements Language
The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in [RFC2119].
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2. Current Practice in IPv4
In current practice, after the LCP and the authentication (if
required) phases are completed, the corresponding network-layer
control protocol, IPCP will be used to negotiate IP layer elements
between subscriber devices and the BNGs.
As in IPv4, PPP is adopted to provide Internet service by a great
many ISPs (both fixed and mobile providers) over a wide area. It is a
simple protocol with following advantages:
1. Robust authentication and authorization functions integrated (PAP
or CHAP), can effectively prevent non-authorized users from
accessing network.
2. Each PPP session is regarded as a separate logical link/interface,
and the process of link establishment is divided into several
orderly phases which are scalable and feasible to be implemented.
3. As a part of PPP, IPCP is fairly efficient. Typically, all the
elements needed for establishing IP connectivity can be configured
through "Configuration Options" defined in IPCP, with no extra
control protocols or devices running these protocols introduced.
4. As a stable method of configuring IP elements, IPCP works well for
the Dial-on-Demand subscriber whose link may be terminated/re-
dialed up anytime.
5. Then, PPP can provide accurate timing and traffic flow statistics
of network access for each subscriber. Base on that, ISPs can
apply various kinds of policies according to different marketing
activities.
6. Broadband user can initiate multiple PPP sessions simultaneously,
each PPP session is dedicated for one service, by this way
services are distinguished and separated by PPP session, in this
case ISP can provide different QoS profile for different service
(PPP session).
3. Problem Statement
While in IPv6, it is not straightforward as in IPv4. Additionally, in
the scenario where the PPP link is initiated by a Residential Gateway,
delegated prefix is required on the CPE as the address pool.
Currently, the configuration of IPv6 link can't be accomplished by
the NCP (IPv6CP) itself.
The lack of Configuration Options defined in IPv6CP results in
following problems:
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o The process of IP elements configuration is quite complicated.
After entering the IPv6CP phase, one or more extra control
protocols such as ND, DHCPv6, (and/or DHCPv6-PD) must be
introduced, as currently there is only one configuration option
define in IPv6CP for interface-ID negotiation.
o The co-existence of multiple mechanisms with functionalities
partially overlapped will lead to interoperation problems in the
implementation.
o More transaction steps caused by extra control protocols
introduced will result in longer response time and higher risk of
exception.
o How to determine the moment when the status of IPv6CP negotiation
comes to "OPEN", so as to get corresponding AAA activities started?
o ISPs have to change current network infrastructure accordingly,
such as installing DHCPv6 server somewhere in the network
(standalone or embedded) which will not only increase both CAPEX
and OPEX, but result in scalability problems when the number of
subscribers grows.
o Some unnecessary functions will be involved. For example,
functions like Address Resolution, On-link Prefix List
Advertisement, Default Router Advertisement, etc. defined in ND
are actually not needed for a simple PPP link.
o Individual active state machine has to be maintained for each
protocol, and conflicts may exist (such as multiple lifetime
counters)
4. Requirements
To keep the implementation simple and stable, the problems described
above must be solved. During the transition from IPv4 to IPv6, if
ISPs choose to run IPv4 and IPv6 over one single PPP link for dual
stack subscribers, it is more feasible to unify the way of
configuring both IPv4 and IPv6.
From the ISP's point of view, it is more reasonable to extend the
IPv6CP functions needed for PPP by the same means of IPCP which is
mature and widely implemented rather than introducing extra control
protocols. To establish basic IPv6 connectivity over PPP, the
following Configuration Options need to be defined:
1. IPv6 address, DNS server addresses (primary and alternative), and
Delegated-Prefix;
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Also, Configuration Options for other fucntions may be considered in
the future:
2. DS-Lite AFTR Address, NTP server address, etc.
5. Security Considerations
There are no security considerations in this document.
6. Acknowledgments
Part of this text borrows from the previous RFCs and I-Ds. And as
such is partially based on previous work done by the PPP working
group. Thanks to Jacni Qin, Qian Wang and Qiong Sun for useful
feedback.
7. References
7.1. Normative References
[RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,
RFC 1661, July 1994.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3315] R. Droms, Ed, J. Bound, B. Volz, T. Lemon, C. Perkins, and
M. Carney, "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", RFC 3315, July 2003.
[RFC3633] O. Troan, R. Droms, "IPv6 Prefix Options for Dynamic Host
Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC3646] R. Droms, Ed, "DNS Configuration options for Dynamic Host
Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
December 2003.
[RFC4861] T. Narten, E. Nordmark, W. Simpson, and H. Soliman, "
Neighbor Discovery for IP version 6 (IPv6)", RFC4861,
September 2007.
[RFC5072] S.Varada, Haskins, D., and E. Allen, "IP Version 6 over
PPP", RFC 5072, September 2007.
7.2. Informative References
[RFC1332] McGregor, G., "The PPP Internet Protocol Control Protocol
(IPCP)", RFC 1332, May 1992.
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[I-D.ietf-pppext-ipv6-dns-addr] Hiller, T. and G. Zorn, "PPP IPV6
Control Protocol Extensions for DNS Server Addresses",
draft-ietf-pppext-ipv6-dns-addr-03 (work in progress), June
2003.
[draft-qin-pppext-ipv6-addr-pref] Y. Li, J. Qin, and L. Yuan, " PPP
IPv6 Control Protocol Extensions for Address and Prefix",
draft-qin-pppext-ipv6-addr-pref-00, January 2010.
[draft-huang-ipv6cp-options] J. Huang, " IPv6CP Options for PPP Host
Configuration", draft-huang-ipv6cp-options-00, February 3,
2010.
Authors' Addresses
Jie Hu
China Telecom Beijing Research Institute
Room 708 No.118, Xizhimenneidajie, xicheng District Beijing 100035
China
Phone: <86 10 58552808>
Email: huj@ctbri.com.cn
Yunqing Chen
China Telecom Beijing Research Institute
Room 708 No.118, Xizhimenneidajie, xicheng District Beijing 100035
China
Phone: <86 10 58552102>
Email: chenyq@ctbri.com.cn
Huiling Zhao
China Telecom Beijing Research Institute
Room 502 No.118, Xizhimenneidajie, xicheng District Beijing 100035
China
Phone: <86 10 58552002>
Email: zhaohl@ctbri.com.cn
Dongfeng Mao
China Telecom
No.31, Jinrong Ave, Xicheng District,100032
Phone: <86 10 58501809>
Email: maodf@chinatelecom.com.cn
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