rfc1375.txt

来自「著名的RFC文档,其中有一些文档是已经翻译成中文的的.」· 文本 代码 · 共 395 行 · 第 1/2 页

Network Working Group                                        P. Robinson
Request for Comments: 1375                        Tansin A. Darcos & Co.
                                                            October 1992


               Suggestion for New Classes of IP Addresses

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard.  Distribution of this memo is
   unlimited.

Abstract

   This RFC suggests a change in the method of specifying the IP address
   to add new classes of networks to be called F, G, H, and K, to reduce
   the amount of wasted address space, and to increase the available IP
   address number space, especially for smaller organizations or classes
   of connectors that do not need or do not want a full Class C IP
   address.

Table of Contents

   Introduction . . . . . . . . . . . . . . . . . . . . . . . . . .   1
   Suggestion for new IP address classes  . . . . . . . . . . . . .   2
       Current Class C Address . . . . . . . . . . . . . . . . . .    3
       Proposed new Class C Address  . . . . . . . . . . . . . . .    4
       Proposed "Class F" address  . . . . . . . . . . . . . . . .    4
       Proposed "Class G" address  . . . . . . . . . . . . . . . .    4
       Proposed "Class H" address  . . . . . . . . . . . . . . . .    5
       Proposed "Class K" address  . . . . . . . . . . . . . . . .    5
   Optional selection of routing codes by region  . . . . . . . . .   5
   Summary  . . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   Notes  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   Security Considerations  . . . . . . . . . . . . . . . . . . . .   7
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . .   7

Introduction

   Currently, IP addresses on the Internet are 32-bit quantities which
   are generally represented as four decimal numbers from 0 to 255,
   separated by periods, sometimes called a "dotted" decimal number.
   The current numbering scheme provides in general for three classes of
   networks in general use (A,B, and C), and two other classes of
   networks (D, E).

   The Class A networks assign a large address space for the particular



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RFC 1375              New Classes of IP Addresses           October 1992


   network to allow up to 254^3 local machines [1].  The Class B network
   assigns a somewhat smaller address space for the particular network
   to allow up to 254^2 local machines.  The Class C network assigns a
   still smaller address space for the particular network to allow up to
   254 local machines.

   This memo proposes to assign part of the unused Class C address space
   for smaller networks than are currently available.  The term "Class
   D" is used for the "multicast" capability and addresses in "Class E"
   are reserved for future use.  Therefore, these new features for which
   capability is to be added is being referred to as classes F, G, H and
   K.

Suggestion for new IP address classes

   The most worrisome problem which appears in the literature is the
   possibility of running out of address space for IP addresses. Various
   schemes are being suggested such as subrouting, introduction of
   additional bits, and other possibilities.

   There is an even more serious matter.  In all probability, I suspect
   that eventually the Internet backbone will either become available to
   anyone who wants to use it (like public highways) and the costs paid
   for out of taxes or some other method which gets someone else to pay
   for it, or eventually the Internet will be fully commercialized and
   made available to anyone who wants to buy a permanent connection.
   With the cost of hardware and connections dropping, some Computer
   Bulletin Board Systems (BBSs) which are currently accessible via
   telephone call may become accessible via TELNET or FTP.  When a 9600
   baud connection can be obtained for around the price of a phone line,
   the demand for internet access will skyrocket.  This almost certain
   eventual availability to virtually anyone who wants a connection will
   cause an even greater demand for internet addresses, which will
   exacerbate this situation.  One problem is in the granularity of IP
   addressing, in that the smallest possible IP address one may obtain
   allows for as high as 254 IP addresses.  If someone wanted only to
   put four or five computers on the Internet, more than 240 addresses
   are wasted.

   Many smaller installations would probably be interested either in
   placing their computers and/or servers on the Internet (and perhaps
   helping to pay the cost of running it) or in being able to access the
   Internet directly, and perhaps making facilities on their machines
   available to others; the problem being that IP addresses on Internet
   are not readily available to small classes of users.  Also, the
   possibility exists of eventually placing non-computer and output-only
   devices such as printers, facsimile machines, and visual pagers
   directly on the Internet to allow people to send a message to a local



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   device simply by directing it to a specific internet site as an E-
   Mail message.

   The scheme proposed by this paper proposes to make a slight change in
   one of the classes of network address in a manner which should not be
   a significant problem for implementing, and should not cause a
   significant hardship as the addresses to use for this purpose are not
   now allocated anyway, and may draw some of the drain which would have
   consumed Class C addresses in large quantity into quantities of Class
   F, H, or K addresses which waste less IP address space.

   This scheme I am proposing is to allow for very small networks (1 or
   2, 1-7, or 1-15, depending on the number of addresses the
   administrator of that site thinks he will need), by reconstructing
   the network address to include what is nominally part of the local
   address.  If bridges and routers (and other hardware and software) do
   not assume that only the last 8 bits make up a local address and
   permit smaller spaces for local addresses, then this method should
   not cause problems. Sites needing less than a close order of 256 IP
   addresses could simply apply for 2 or more contiguous blocks of Class
   F numbers.

   Currently, a Class C address consists of a 32-bit number in which the
   leftmost 3 bits consist of "110" [2]:

        The third type of address, class C, has a 21-bit network number
        and a 8-bit local address.  The three highest-order bits are set
        to 1-1-0.  This allows 2,097,152 class C networks.

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |1 1 0|                    NETWORK              | Local Address |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Current Class C Address

   This memo proposes to change Class C addresses to be 4-bit numbers
   beginning with "1100":

   The third type of address, class C, has a 20-bit network number and a
   8-bit local address.  The four highest-order bits are set to 1-1-0-0,
   This allows 1,048,576 class C networks.








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RFC 1375              New Classes of IP Addresses           October 1992


                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |1 1 0 0|                  NETWORK              | Local Address |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Proposed new Class C Address

   This memo then proposes to add four new types of addresses, to be
   referred to as "Class F", "Class G", "Class H", and "Class K" [3].
   These would all use part of the "old" class C address by all using IP
   addresses that begin with the 4-bit sequence "1101".  The Class F
   addresses would begin with the binary code sequence "11010", Class G
   addresses begin with "110110", Class H addresses with "1101110", and
   Class K with "1101111".

   Class F addresses will be used for networks having from 1-15 sites
   [4], where the number could be expected to exceed 7.  Class F
   addresses are defined as follows:

   The sixth type of address, class F, has a 23-bit network number, and
   a 4-bit local address.  The five highest-order bits are set to 1-1-
   0-1-0.  This allows 16,777,256 class F networks.