Internet Engineering Task Force (IETF) J. Mitchell
Request for Comments: 6996 Microsoft Corporation
BCP: 6 July 2013
Category: Best Current Practice
Autonomous System (AS) Reservation for Private Use
This document describes the reservation of Autonomous System Numbers
(ASNs) that are for Private Use only, known as Private Use ASNs, and
provides operational guidance on their use. This document enlarges
the total space available for Private Use ASNs by documenting the
reservation of a second, larger range and updates RFC 1930 by
replacing Section 10 of that document.
Status of This Memo
This memo documents an Internet Best Current Practice.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
BCPs is available in Section 2 of RFC 5741.
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Mitchell Best Current Practice [Page 1]RFC 6996 Private Use AS Reservation July 20131. Introduction
The original IANA reservation of Autonomous System Numbers (ASNs) for
Private Use was a block of 1023 ASNs. This was also documented by
the IETF in Section 10 of [RFC1930]. Since the time that the range
was reserved, the Border Gateway Protocol (BGP) [RFC4271] has seen
deployment in new application domains, such as data center networks,
which require a larger Private Use AS space.
Since the introduction of "BGP Support for Four-Octet Autonomous
System (AS) Number Space" [RFC6793], the total size of ASN space has
increased dramatically. A larger subset of the space is available to
network operators to deploy in these Private Use cases. The existing
range of Private Use ASNs is widely deployed, and the ability to
renumber this resource in existing networks cannot be coordinated
given that these ASNs, by definition, are not registered. Therefore,
this RFC documents the existing Private Use ASN reservation while
also introducing a second, larger range that can also be utilized.
2. 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 RFC 2119 [RFC2119].
3. Private Use ASNs
To allow the continued growth of BGP protocol usage in new network
applications that utilize Private Use ASNs, two ranges of ASNs are
reserved by Section 5 of this document. The first is part of the
original 16-bit Autonomous System range previously defined in
[RFC1930], and the second is a larger range out of the Four-Octet AS
Number Space [RFC6793].
4. Operational Considerations
If Private Use ASNs are used and prefixes originate from these ASNs,
Private Use ASNs MUST be removed from AS path attributes (including
AS4_PATH if utilizing a four-octet AS number space) before being
advertised to the global Internet. Operators SHOULD ensure that all
External Border Gateway Protocol (EBGP) speakers support the
extensions described in [RFC6793] and that implementation-specific
features that recognize Private Use ASNs have been updated to
recognize both ranges prior to making use of the newer, numerically
higher range of Private Use ASNs in the four-octet AS number space.
Some existing implementations that remove Private Use ASNs from the
AS_PATH are known to not remove Private Use ASNs if the AS_PATH
contains a mixture of Private Use and Non-Private Use ASNs. If such