Autonomous System (AS) Number Reservation for Documentation Use
Sets aside fake network numbers to prevent confusion in examples
Huston, G., "Autonomous System (AS) Number Reservation for Documentation Use", RFC 5398, DOI 10.17487/RFC5398, December 2008, <https://www.rfc-editor.org/info/rfc5398>.
@misc{rfc5398,
series = {Request for Comments},
number = 5398,
howpublished = {RFC 5398},
publisher = {RFC Editor},
doi = {10.17487/RFC5398},
url = {https://www.rfc-editor.org/info/rfc5398},
author = {G. Huston},
title = {{Autonomous System (AS) Number Reservation for Documentation Use}},
pagetotal = 4,
year = 2008,
month = dec,
} RFC text
Contents
Network Working Group G. Huston
Request for Comments: 5398 December 2008
Category: Informational
Autonomous System (AS) Number Reservation for Documentation Use
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) 2008 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (http://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Abstract
To reduce the likelihood of conflict and confusion when relating
documented examples to deployed systems, two blocks of Autonomous
System numbers (ASNs) are reserved for use in examples in RFCs,
books, documentation, and the like. This document describes the
reservation of two blocks of ASNs as reserved numbers for use in
documentation.
1. Introduction
To reduce the likelihood of conflict and confusion when relating
documented examples to deployed systems, two blocks of Autonomous
System numbers (ASNs) are reserved for use in examples in RFCs,
books, documentation, and the like. This document describes the
reservation of two blocks of ASNs as reserved numbers for use in
documentation.
The problems such conflicts may cause have already been encountered
with IPv4 addresses where literal use of documented examples in a
production environment causes address and routing conflicts with
existing services. Since private-use ASNs already have a context of
use in deployed networks, these ASNs cannot be used in many example
situations. In making an explicit allocation of a set of AS numbers
reserved for documentation use, it is intended that any such
operational problems may be avoided in the future.
Similar considerations have been applied to IPv4 addresses
[IANA.IPv4], IPv6 addresses [RFC3849], and domain names [RFC2606],
and reservations have been made for similar purposes.
2. ASNs for Documentation Use
To allow documentation to accurately describe deployment examples,
the use of public or private-use AS numbers is inappropriate, and a
reserved block of AS numbers is required. This ensures that
documentation does not clash with public- or private-use AS numbers
in deployed networks, and mitigates the risks to operational
integrity of the network through inappropriate use of documentation
to perform literal configuration of routing elements on production
systems.
To allow for examples relating to the transition to use of 32-bit AS
numbers to be correctly described, a reservation of two blocks of AS
numbers is proposed in this document. One reserved block of 16
contiguous AS numbers is to lie in the range of numbers that can be
expressed as a 16-bit AS number value (i.e., values less than 65536),
and a second reserved block of 16 contiguous AS numbers is to lie in
the range of numbers that can only be expressed as 32-bit AS numbers
(values greater than 65535).
3. Operational Implications
This assignment implies that BGP operational configurations should
not peer with neighboring ASes that are numbered from this reserved
AS number set.
4. IANA Considerations
IANA has reserved a contiguous block of 16 Autonomous System numbers
from the unallocated number range within the "16-bit" number set for
documentation purposes, namely 64496 - 64511, and a contiguous block
of 16 Autonomous System numbers from the "32-bit" number set for
documentation, namely 65536 - 65551. These reservations have been
documented in the IANA AS Number Registry [IANA.AS].
5. Security Considerations
AS number reservations do not have any direct impact on Internet
infrastructure security.
6. Acknowledgements
The author acknowledges the work of Tomoya Yoshida, Gaurab Upadhaya,
and Philip Smith in authoring a policy proposal that was submitted to
the APNIC Policy Process in 2008 relating to the reservation of AS
numbers for documentation purposes.
7. Informative References
[IANA.AS] IANA, "Autonomous System (AS) Numbers", Sep 2008,
<http://www.iana.org>.
[IANA.IPv4] IANA, "IPv4 Global Unicast Address Assignments",
Sep 2008, <http://www.iana.org>.
[RFC2606] Eastlake, D. and A. Panitz, "Reserved Top Level DNS
Names", BCP 32, RFC 2606, June 1999.
[RFC3849] Huston, G., Lord, A., and P. Smith, "IPv6 Address Prefix
Reserved for Documentation", RFC 3849, July 2004.
Author's Address
Geoff Huston
EMail: gih@apnic.net
AI ELI5
On this page
§1The Example Problem
RFC authors, textbook writers, and network engineers need to use Autonomous System numbers in examples to explain how BGP (Border Gateway Protocol) and routing work. If they use real AS numbers, someone might copy the example into production, causing conflicts with actual deployed networks. This document reserves specific AS numbers exclusively for documentation use, avoiding the real-world problems that IPv4 and IPv6 address documentation ranges already solved.
When you write an example about how networks talk to each other, you need to make-up AS numbers so nobody gets confused and wires up your example by mistake.
§2The Reserved Blocks
IANA reserves two blocks of 16 contiguous AS numbers. One block lies in the 16-bit AS number range: 64496 to 64511 (expressions as 16-bit values). The second block is in the 32-bit range: 65536 to 65551 (values that require 32-bit representation). Splitting the reservations allows documentation to show examples of both traditional 16-bit AS numbering and newer 32-bit AS numbering transition scenarios.
There are two sets of fake AS numbers: one for old-style numbers and one for new-style numbers. Each set has 16 numbers to use in examples.
§3Operational Use
BGP routers and operational configurations must never peer with AS numbers from these reserved ranges. This ensures that even if someone accidentally configures documentation examples on live equipment, the reserved AS numbers will not establish real BGP relationships. The reservations are recorded in the IANA AS Number Registry, making them official and universally recognized.
Real routers should never try to connect to these fake AS numbers, so even if an example accidentally gets configured in production, it will not work.