Requirements for IPv6 Prefix Delegation
What a system for distributing IPv6 addresses to customers should do.
Miyakawa, S. and R. Droms, "Requirements for IPv6 Prefix Delegation", RFC 3769, DOI 10.17487/RFC3769, June 2004, <https://www.rfc-editor.org/info/rfc3769>.
@misc{rfc3769,
series = {Request for Comments},
number = 3769,
howpublished = {RFC 3769},
publisher = {RFC Editor},
doi = {10.17487/RFC3769},
url = {https://www.rfc-editor.org/info/rfc3769},
author = {S. Miyakawa and R. Droms},
title = {{Requirements for IPv6 Prefix Delegation}},
pagetotal = 6,
year = 2004,
month = jun,
} RFC text
Contents
Network Working Group S. Miyakawa
Request for Comments: 3769 NTT Communications Corporation
Category: Informational R. Droms
Cisco
June 2004
Requirements for IPv6 Prefix Delegation
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2004).
Abstract
This document describes requirements for how IPv6 address prefixes
should be delegated to an IPv6 subscriber's network (or "site").
1. Introduction
With the deployment of IPv6 [1], several Internet Service Providers
are ready to offer IPv6 access to the public. In conjunction with
widely deployed "always on" media such as ADSL and the expectation
that customers will be assigned a /48 IPv6 unicast address prefix
(see RFC 3513 [3] and section 3 of RFC 3177 [2]), an efficient
mechanism for delegating address prefixes to the customer's sites is
needed. The delegation mechanism will be intended to automate the
process of informing the customer's networking equipment of the
prefixes to be used at the customer's site.
This document clarifies the requirements for IPv6 address prefix
delegation from the ISP to the site.
2. Scenario and terminology
The following figure illustrates a likely example for the
organization of a network providing subscription IPv6 service:
/------\
/ \
+ |
/ \ /
+---------------+ +--------+/ \------/
|ISP Edge Router|Point-to-point|Customer+
| +--------------+ Router | Customer networks
| (PE) | link | (CPE) +
+---------------+ +--------+\ /------\
\ / \
+ |
\ /
\------/
Figure 1: Illustration of ISP-customer network architecture
Terminology:
PE: Provider edge device; the device connected to the service
provider's network infrastructure at which the link to the
customer site is terminated
CPE: Customer premises equipment; the device at the customer site at
which the link to the ISP is terminated
3. Requirements for Prefix Delegation
The purpose of the prefix delegation mechanism is to delegate and
manage prefixes to the CPE automatically.
3.1. Number and Length of Delegated Prefixes
The prefix delegation mechanism should allow for delegation of
prefixes of lengths between /48 and /64, inclusively. Other lengths
should also be supported. The mechanism should allow for delegation
of more than one prefix to the customer.
3.2. Use of Delegated Prefixes in Customer Network
The prefix delegation mechanism must not prohibit or inhibit the
assignment of longer prefixes, created from the delegated prefixes,
to links within the customer network. The prefix delegation
mechanism is not required to report any prefix delegations within the
customer's network back to the ISP.
3.3. Static and Dynamic Assignment
The prefix delegation mechanism should allow for long-lived static
pre-assignment of prefixes and for automated, possibly short-lived,
on-demand, dynamic assignment of prefixes to a customer.
3.4. Policy-based Assignment
The prefix delegation mechanism should allow for the use of policy in
assigning prefixes to a customer. For example, the customer's
identity and type of subscribed service may be used to determine the
address block from which the customer's prefix is selected, and the
length of the prefix assigned to the customer.
3.5. Expression of Requirements or Preferences by the CPE
The CPE must be able to express requirements or preferences in its
request to the PE. For example, the CPE should be able to express a
preference for a prefix length.
3.6. Security and Authentication
The prefix delegation mechanism must provide for reliable
authentication of the identity of the customer to which the prefixes
are to be assigned, and must provide for reliable, secure
transmission of the delegated prefixes to the customer.
The prefix delegation should provide for reliable authentication of
the identity of the service provider's edge router.
3.7. Accounting
The prefix delegation mechanism must allow for the ISP to obtain
accounting information about delegated prefixes from the PE.
3.8. Hardware technology Considerations
The prefix delegation mechanism should work on any hardware link
technology between the PE and the CPE and should be hardware
technology independent. The mechanism must work on shared links.
The mechanism should work with all hardware technologies with either
an authentication mechanism or without, but ISPs would like to take
advantage of the hardware technology's authentication mechanism if it
exists.
4. Security considerations
Section 3.6 specifies security requirements for the prefix delegation
mechanism. For point to point links, where one trusts that there is
no man in the middle, or one trusts layer two authentication,
authentication may not be necessary.
A rogue PE can issue bogus prefixes to a requesting router. This may
cause denial of service due to unreachability.
A rogue CPE may be able to mount a denial of service attack by
repeated requests for delegated prefixes that exhaust the PE's
available prefixes.
5. Acknowledgments
The authors would like to express thanks to Randy Bush, Thomas
Narten, Micheal Py, Pekka Savola, Dave Thaler, as well as other
members of the IPv6 working group and the IESG for their review and
constructive comments. The authors would also like to thank the
people in the IPv6 operation group of the Internet Association of
Japan and NTT Communications IPv6 project, especially Toshi Yamasaki
and Yasuhiro Shirasaki for their original discussion and suggestions.
6. Informative References
[1] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998.
[2] IAB and IESG, "IAB/IESG Recommendations on IPv6 Address", RFC
3177, September 2001.
[3] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6)
Addressing Architecture", RFC 3513, April 2003.
7. Authors' Addresses
Shin Miyakawa
NTT Communications Corporation
Tokyo
Japan
Phone: +81-3-6800-3262
EMail: miyakawa@nttv6.jp
Ralph Droms
Cisco
1414 Massachusetts Avenue
Boxborough, MA 01719
USA
Phone: +1 978.936.1674
EMail: rdroms@cisco.com
8. Full Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject
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AI ELI5
On this page
§1The Challenge of IPv6 Distribution
As IPv6 deployment began in the early 2000s, ISPs needed a way to automatically distribute IPv6 address prefixes to customer networks. The traditional model of assigning a few addresses per household was not practical for IPv6, where each customer site was expected to receive a /48 prefix—a block with enough addresses for thousands of subnets within the customer's network.
The document describes the requirements for a prefix delegation mechanism: a system by which an ISP's edge router (the provider equipment) can automatically inform each customer's equipment (the customer router) which address blocks belong to that customer. Without an automated mechanism, ISPs would manually configure each customer's addresses, an operation that does not scale to millions of subscribers.
IPv6 gives each home office or location its own big block of addresses. An ISP needs a fast, automatic way to tell each customer which block is theirs, without a person having to type it in by hand.
§2ISPs, Customers, and Networks
The RFC describes a simple network setup: an ISP has a provider edge (PE) device connected via a point-to-point link to a customer premises equipment (CPE) device at the customer site. The CPE sits at the boundary of the customer's internal networks. The prefix delegation system allows the PE to send prefixes to the CPE, which then uses them to configure its own networks.
The customer's equipment must then distribute those prefixes within the customer's own network, assigning pieces of the delegated block to different subnets, servers, or devices. The delegation mechanism is not responsible for this internal distribution; it only handles the boundary between the ISP and the customer.
Imagine a mailroom at a company. The ISP is the post office, the customer's router is the mailroom, and the company's subnets are the different departments. The delegation system gets addresses from the post office to the mailroom, and the mailroom handles giving them to the departments.
§3What a Good Delegation System Must Do
The RFC lists eight key requirements for a prefix delegation mechanism.
Flexible prefix sizes: The system should support delegating prefixes of /48 to /64 length, and ideally other lengths as well. Customers should be able to receive multiple prefixes, not just one. Internal freedom: Once the customer receives a prefix, they can subdivide it into longer, more specific prefixes for their own use; the delegation system should not restrict this.
Static and dynamic: The system should support both long-lived, pre-assigned prefixes for stable customers and automatic, on-demand assignment for mobile or temporary connections. Policy-based: The ISP should be able to use customer identity, service level, or other policy to decide which address block to assign and how long it lasts.
Customer preferences: The customer router should be able to request a specific prefix length or other parameters, and the ISP system should honor reasonable requests. Security: Both the customer and ISP must authenticate each other, and the delegated prefixes must be transmitted securely. Accounting: The PE must be able to record which prefixes were assigned to which customers for billing and management. Hardware independence: The mechanism must work over any link type—Ethernet, PPP, DSL—and must work on shared links where multiple customers connect to the same PE.
A good prefix delegation system is flexible: the ISP can give out different sizes of address blocks, let customers ask for what they want, lock down security so nobody fakes being a customer, and work over any type of connection from home internet to business lines.
§4Security and Reliability
The RFC identifies several security concerns for prefix delegation. A rogue or compromised PE could issue bogus prefixes to a customer, potentially creating a denial of service if those prefixes conflict with legitimate ones or cannot be routed. A malicious customer could repeatedly request many prefixes in an attempt to exhaust the ISP's address space.
For point-to-point links with physical security or layer-two authentication, explicit authentication of the delegation protocol may not be strictly necessary. However, for any shared or untrusted link, strong mutual authentication of both the PE and the CPE is essential. The delegated prefixes themselves must be protected in transit to prevent eavesdropping or tampering.
A bad router could hand out fake addresses and mess up delivery. A bad customer could ask for so many addresses that the ISP runs out. Both sides need to prove they're who they claim to be before handing over address blocks.