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Analysis of the 64-bit Boundary in IPv6 Addressing (RFC7421) Disclosure Number: IPCOM000240238D
Original Publication Date: 2015-Jan-01
Included in the Prior Art Database: 2015-Jan-15
Document File: 48 page(s) / 60K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

B. Carpenter: AUTHOR [+6]


Rather than simply overcoming the IPv4 address shortage by doubling the address size to 64 bits, IPv6 addresses were originally chosen to be 128 bits long to provide flexibility and new possibilities. In particular, the notion of a well-defined interface identifier was added to the IP addressing model. The IPv6 addressing architecture [RFC4291] specifies that a unicast address is divided into n bits of subnet prefix followed by (128-n) bits of interface identifier (IID). The bits in the IID may have significance only in the process of deriving the IID; once it is derived, the entire identifier should be treated as an opaque value [RFC7136]. Also, since IPv6 routing is entirely based on variable length prefixes (also known as variable length subnet masks), there is no basic architectural assumption that n has any particular fixed value. All IPv6 routing protocols support prefixes of any length up to /128.

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Internet Engineering Task Force (IETF)                 B. Carpenter, Ed. Request for Comments: 7421                             Univ. of Auckland Category: Informational                                         T. Chown ISSN: 2070-1721                                     Univ. of Southampton                                                                  F. Gont                                                   SI6 Networks / UTN-FRH                                                                 S. Jiang                                             Huawei Technologies Co., Ltd                                                              A. Petrescu                                                                CEA, LIST                                                           A. Yourtchenko                                                                    Cisco                                                             January 2015

            Analysis of the 64-bit Boundary in IPv6 Addressing


   The IPv6 unicast addressing format includes a separation between the    prefix used to route packets to a subnet and the interface identifier    used to specify a given interface connected to that subnet.    Currently, the interface identifier is defined as 64 bits long for    almost every case, leaving 64 bits for the subnet prefix.  This    document describes the advantages of this fixed boundary and analyzes    the issues that would be involved in treating it as a variable    boundary.

Status of This Memo

   This document is not an Internet Standards Track specification; it is    published for informational purposes.

   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).  Not all documents    approved by the IESG are a candidate for any level of Internet    Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,    and how to provide feedback on it may be obtained at

 Carpenter, et al.             Informational        ...