Pppext WG Jie. Hu
Internet-Draft Yunqing. Chen
Intended status: Standards Track Dongfeng. Mao
Expires: September 15, 2011 China Telecom
Haoxin. Tang
China Unicom
March 14, 2011
PPPv6 Problem statement and requirements
draft-hu-pppext-ipv6cp-requirements-01
Abstract
As in IPv4 network, PPP (PPPoE) will still be an important mechanism
to provide access services to broadband subscribers of IPv6 or dual-
stack. This document describes problems the ISPs faced when
deploying IPv6 in broadband access network over PPP, particularly,
the capabilities lacked in IPv6CP.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 3
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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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.
While based on the current capabilities of the IPv6 Control Protocol
( IPv6CP) which is used for the negotiation of IPv6 parameters over
PPP, only Interface-Identifier can be negotiated, other parameters
such as IPv6 Address, DNS server addresses and delegated prefix have
to be configured by other means rather than IPv6CP.
1.1. 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].
2. Problem Statement
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 all the IP layer
elements needed between subscriber devices and the Broadband Network
Gateway ( BNG). This is fairly an efficient and robust means which
collaborates quite well with other mechanisms like those for AAA,
when providing access services in variable environments.
While in IPv6 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:
1. 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. Additionally, the
status 'OPEN' of IPv6CP negotiation cannot be treated as the sign
of access service!_s ready and triggers corresponding AAA
activities, for instance' Accounting START'.
2. 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.
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3. The co-existence of multiple protocols with functionalities
partially overlapped will lead to interoperation problems in the
implementation as individual active state machine has to be
maintained for each protocol which can result in conflicts (such
as multiple lifetime counters). Additionally, more transaction
steps caused by extra control protocols introduced will result in
longer response time and higher risk of exception.
4. ISPs have to change current network infrastructure accordingly,
such as installing new DHCPv6 servers somewhere in the network (
standalone or embedded) which will increase both CAPEX and OPEX.
5. 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.
6. At the LNS, if we filter traffic to be from the router IP
addresses on all of our DSL lines to avoid spoofing, the FE80::
link local address is not allowed through the source filtering as
it is link local and so not allowed on to the network. This
filtering has to be modified to allow FE80:: addresses for SLAAC
or DHCPv6 but then be blocked at a later stage.
3. 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;
2. Delegated IPv6 prefix;
3. DNS server addresses (primary and alternative);
Also, Configuration Options for other functions may be considered in
the future.
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4. Acknowledgements
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.
5. IANA Considerations
This document includes no request to IANA.
6. Security Considerations
No new security concerns raised out of this document.
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] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC3646] Droms, R., "DNS Configuration options for Dynamic Host
Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
December 2003.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC5072] S.Varada, Haskins, D., and E. Allen, "IP Version 6 over
PPP", RFC 5072, September 2007.
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7.2. Informative References
[I-D.huang-ipv6cp-options]
Huang, J., "IPv6CP Options for PPP Host Configuration",
draft-huang-ipv6cp-options-00 (work in progress),
February 2010.
[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.
[I-D.qin-pppext-ipv6-addr-pref]
Li, Y., Qin, J., and L. Yuan, "PPP IPv6 Control Protocol
Extensions for Address and Prefix",
draft-qin-pppext-ipv6-addr-pref-00 (work in progress),
February 2010.
[RFC1332] McGregor, G., "The PPP Internet Protocol Control Protocol
(IPCP)", RFC 1332, May 1992.
Authors' Addresses
Jie Hu
China Telecom
Room 708 No.118, Xizhimenneidajie
Beijing, 100035
China
Phone: +86 10 5855 2808
Email: huj@ctbri.com.cn
Yunqing Chen
China Telecom
Room 708 No.118, Xizhimenneidajie
Beijing, 100035
China
Phone: +86 10 5855 2102
Email: chenyq@ctbri.com.cn
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Dongfeng Mao
China Telecom
No.31, Jinrong Ave
Beijing, 100032
China
Phone: +86 10 5850 1809
Email: maodf@chinatelecom.com.cn
Haoxin Tang
China Unicom
No.13, Jinrong Ave
Beijing, 100035
China
Phone: +86 1860 110 1695
Email: tanghx@chinaunicom.cn
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