Autonomous System (AS) Reservation for Private Use
draft-mitchell-idr-as-private-reservation-00

Abstract

This document describes the reservation of Autonomous System numbers (ASNs) that may be used within networks but should not be advertised to the Internet, known as private use ASNs. This document enlarges the total space available for private use ASNs by documenting the reservation of a second larger range and updates RFC 1930.

Status of this Memo

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This Internet-Draft will expire on December 20, 2012.

Copyright Notice

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1. Introduction

The original IANA reservation of ASNs for private use was a block of 1023 ASNs. This was documented by IETF in Section 10 of [RFC1930] that specified the private use ASN range as 64512 through 65535 (implying the inclusion of ASN 65535). Since that range was reserved and documented over a decade ago, BGP has seen much wider deployment in Service Provider, Enterprise and Content Provider networks. The use cases in these networks for private use ASNs include networks that are attached to the Internet, utilizing implementation specific features to remove them upon advertisement to Internet peers, and networks that are not attached to the Internet. The displacement of Frame Relay and ATM based VPNs by BGP/MPLS IP VPNs [RFC4364] has also increased the deployment of BGP to a larger number of sites, especially for networks with requirements for multi-homing or provider redundancy.

The limited size of the current range of private use ASNs has led to the usage of a number of implementation specific features that manipulate the AS_PATH or remove AS_PATH based loop prevention described in Section 9 of [RFC4271]. These workarounds have increased the operational complexity of the networks since the implementations of these functions vary and have been largely out of scope of existing BGP standards.

Since the introduction of BGP Support for Four-octet AS Number Space [RFC4893], the total size of the ASN space has increased dramatically, and a larger subset of the space should be available to network operators to deploy in private use cases. The existing range of private use ASNs is widely deployed and the ability to renumber this resource for reassignment in existing networks cannot be coordinated given these ASNs by definition are not registered. Therefore this document clarifies the existing ASN range, while introducing a second, larger, range that can also be utilized.

2. Private Use ASNs

To allow the continued growth of usage of the BGP protocol in networks that utilize private ASNs two ranges of ASNs are reserved by this document in Section 5. The first which was previously defined in [RFC1930] out of the original 16-bit Autonomous System range and a second, larger, reserved block available out of the higher part of the Four-Octet AS Number Space [RFC4893].

3. Operational Considerations

If private use ASNs are used and prefixes are originated from these private use ASNs which are destined to the Internet, private use ASNs must be removed from the AS_PATH before being advertised to the global Internet. Prior to making use of the second, numerically higher, range of these ASNs network operators should be confident any implementation specific features or filters that recognize private use ASNs have been updated to recognize both ranges correctly so that no unintended announcement of private use ASNs to the Internet occurs.

4. Acknowledgements

The author would like to acknowledge Christopher Morrow and Jason Schiller for their advice on how to pursue this change.

5. IANA Considerations

[Note to IANA, not for publication: The IANA may wish to consider updating the existing private use AS number reservation to explicitly include ASN 65535 that has been documented in RFC 1930 as well as implemented in a number of implementations that recognize private use ASNs as part of the existing range. Further, to maintain consistency from an operator standpoint, it is suggested that the end of the "32-bit number set" be reserved for Private Use, and a size of 967,295 is suggested corresponding to the range of 4294000000 to 4294967295 inclusive, primarily motivated by being visibly recognizable while not consuming a large portion of the total ASN space.]

[Note to WG, not for publication: a small poll of network implementers was taken and it was not felt optimizing the range to a bit boundary was important for control plane performance of any features that recognize private use ASNs - others in WG may want to weigh in here. Also very interested in feedback on appropriate sizing of the future range given the many current and future uses of BGP in networks]

(If approved) IANA has reserved, for Private Use, a contiguous block of TBD (1023 or 1024) Autonomous System numbers from the "16-bit Autonomous System Numbers" registry, namely 64512 - TBD1 (65534 or 65535) inclusive.

(If approved) IANA has also reserved, for Private Use, a contiguous block of TBD Autonomous System numbers from the "32-bit Autonomous System Numbers" registry, namely TBD2 - TBD3 inclusive.

(If approved) These reservations have been documented in the IANA AS Number Registry [IANA.AS].

6. Security Considerations

This document does not introduce any additional security concerns in regards to private use ASNs.

7. References

7.1. Normative References

7.2. Informative References

Author's Address

Table of Contents

• 1. Introduction
• 2. Private Use ASNs
• 3. Operational Considerations
• 4. Acknowledgements
• 5. IANA Considerations
• 6. Security Considerations
• 7. References
• 7.1. Normative References
• 7.2. Informative References
• Author's Address