Using 31-Bit Prefixes on IPv4 Point-to-Point Links (RFC3021)
Original Publication Date: 2000-Dec-01
Included in the Prior Art Database: 2019-Feb-14
Internet Society Requests For Comment (RFCs)
A. Retana: AUTHOR [+3]
With ever-increasing pressure to conserve IP address space on the Internet, it makes sense to consider where relatively minor changes can be made to fielded practice to improve numbering efficiency. One such change, proposed by this document, is to halve the amount of address space assigned to point-to-point links (common throughout the Internet infrastructure) by allowing the use of 31-bit subnet masks in a very limited way. [STANDARDS-TRACK]
Network Working Group A. Retana Request for Comments: 3021 R. White Category: Standards Track Cisco Systems V. Fuller GTE Internetworking D. McPherson Amber Networks December 2000
Using 31-Bit Prefixes on IPv4 Point-to-Point Links
Status of this Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (2000). All Rights Reserved.
With ever-increasing pressure to conserve IP address space on the Internet, it makes sense to consider where relatively minor changes can be made to fielded practice to improve numbering efficiency. One such change, proposed by this document, is to halve the amount of address space assigned to point-to-point links (common throughout the Internet infrastructure) by allowing the use of 31-bit subnet masks in a very limited way.
1. Introduction and Motivation
The perceived problem of a lack of Internet addresses has driven a number of changes in address space usage and a number of different approaches to solving the problem:
- More stringent address space allocation guidelines, enforced by the IANA and the regional address assignment authorities [RFC2050].
- Use of Network Address Translators (NATs), where a small number of IANA-compliant addresses are shared by a larger pool of private, non-globally routed addresses topologically behind a NAT box [RFC1631].
Retana, et al. Standards Track [Page 1]
RFC 3021 31-Bit Prefixes on IPv4 Links December 2000
- Deployment of a new Internet Protocol to increase the size of the address space. One such protocol, IPv6 [RFC2460], has been through the IETF process but has yet to see production deployment. Should it be, deployed, it will still face a many year transition period.
Prior to the availability of a larger address space, it seems prudent to consider opportunities for making more efficient use of the existing address space.
One such (small) opportunity is to change the way that point-to-point links are numbered. One option, which is used today on some parts of the Internet, is to simply not number point-to-point links between routers. While this practice may seem, at first, to handily resolve the problem, it causes a number of problems of its own, including the inability to consistently manage the unnumbered link or reach a router through it, difficulty in management and debugging of those links, and the lack of standardization [RFC1812].
In current practice, numbered Internet subnets do not use longer than a 30-bit subnet mask (in most cases), which requires four addresses per link - two host addresses, one all-zeros network, and one all- ones broadcast. This is unfortunate for point-to-point links, since they can only possibly have two i...