Bill Manning


                                                      03 January 2001



            Documenting Special Use IPv4 Address Blocks

            that have been registered with IANA



1. Status of this Memo


This draft, file name draft-manning-dsua-04.txt, is intended to become

something that might be of use to those who are interested in the

operational requirements of an IPv4 based network.  It does not specify

an Internet standard of any kind. Distribution of this document is

unlimited. Comments should be sent to the author.


This document is an Internet-Draft and is NOT offered in accordance with

Section 10 of RFC2026, and the author does not provide the IETF with any

rights other than to publish as an Internet-Draft.


Internet-Drafts are working documents of the Internet Engineering Task

Force (IETF), its areas, and its working groups.  Note that other groups

may also distribute working documents as Internet-Drafts.


Internet-Drafts are draft documents valid for a maximum of six months and

may be updated, replaced, or obsoleted by other documents at any time.  It

is inappropriate to use Internet-Drafts as reference material or to cite

them other than as "work in progress."


The list of current Internet-Drafts can be accessed at



The list of Internet-Draft Shadow Directories can be accessed at



Copyright Notice


   Copyright (C) The Internet Society (2000).  All Rights Reserved.





This document lists the existent special use prefixes from the IPv4 space

that have been registered with the IANA and provides some suggestions for

operational procedures when these prefixes are encountered.  This document

does not address IPv4 space that is not registered with the IANA for special

use or address space that is reserved for future delegation in the

operational Internet.


The current list of special use prefixes:

      all D/E space


2.1 Prefix Discussion: has a number of unique properties, many of which were built into

the protocol stacks used throughout the Internet. or the all-zeros

address has been used and is still recognized as the historical broadcast

address. This use or restriction is deprecated and modern code will treat

broadcast correctly as an all-ones value within the subnet. It is fairly

common practice to use to encode the idea of "default".


Also, many stacks will allow the system administrator to encode IP addresses

of the form, with the presumption that historical, "natural" masks

apply and so this would represent a host that carries the local value of

x.x.160.57 within the /16 net-block that is in use on that media. These

properties suggest that a prudent network manager & system admin will treat as a special use net-block. Router and Host requirements documents

and implementations treat this range with special use constraints. is earmarked for what is called "loop-back". This construct is

to allow a node to test/validate its IP stack.  Most software only uses

a single value from this range, for loop-back purposes.  It

is treated with the same levels of restriction by router and host requirements

and implementations so it is difficult to use any other addresses within

this block for anything other than node specific applications, generally

bootstrapping.  All in all a tremendous waste of IP space. Good thing we'll

not likely need it. is listed as the TEST-NET. This prefix is earmarked for use in

documentation and example code. Network operations and End System

administrators should ensure that this prefix is not coded into systems

or routed through any infrastructure.  Since it has the appearance of a

"normal" prefix, special precautions should be taken to ensure that this

prefix is not propagated in either the Internet or any private networks

that use the IP protocols.  Often used in conjunction with

or in vendor and protocol documentation.,, are the prefixes called out

in RFC 1918. They are only for use in private networks that wish to use

the IP protocols. Network operations and End System administrators should

ensure that applications do not use these ranges as source or destination

addresses for any packets that traverse the Internet infrastructure.  Since

they have the appearance of "normal" prefixes, special precautions should be

taken to ensure that they are not propagated in the Internet. has been ear-marked as the IP range to use for end node

auto-configuration when a DHCP server may not be found. As such, network

operations and administrators should be VERY aggressive in ensuring that

neither route advertisements nor packet forwarding should occur across

any media boundaries. This is true for the Internet as well as any

private networks that use the IP protocols. End node administrators

should be aware that some vendors will auto-configure and add this

prefix to the nodes forwarding table. This will cause problems with

sites that run router discovery or deprecated routing protocols such as



Class D & E space. These are parts of the IPv4 space that retain some context

of class-fullness. They are used for identification of multicast and a range

left unspecified.  Multicast is perfectly legal and has valid public uses but

some care is required in understanding its appropriate use. The "E" space is

still unspecified and so should be avoided. This extract from RFC 1166 covers

these ranges.


      The fourth type of address, class D, is used as a multicast

      address [13].  The four highest-order bits are set to 1-1-1-0.



                            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 1 0|                  multicast address                    |



                                 Class D Address



      Note:  No addresses are allowed with the four highest-order bits

      set to 1-1-1-1.  These addresses, called "class E", are reserved.


As a side note, at least one vendor has hijacked an address range for

use by its printservers. That range is and the specific

address that they use is  This is not a valid delegation

to this vendor and its use argues for re-constitution of this service

into the link-local range or configurable with site delegated space.


3. DNS considerations:


None of these address prefixes, save multicast, is to be used or visible on

the public Internet.  In fact, some of these prefixes must not appear outside

the machine. To encourage honesty, most of these prefixes have been mapped to

authoritative servers in the DNS at the request of the IANA. This encourages

people to ensure that when used, these prefixes are coded with local-scope

DNS and there will be no "leakage" to the global Internet.


4. Access Control suggestions:


In todays network, it is prudent to control access. In the case of these

special use prefixes, it is generally a good idea to filter them so they

do not propagate. After all, you don't want someone else's use of these

prefixes to taint your environment. All of these address classes should be

invalid as source addresses (except where negotiated in advance), and very

few should be permitted as destination addresses (Multicast for example,

should be permitted as a destination, just not as a source).  An example of

one form of access control is listed below:



access-list 100 deny   ip host any

access-list 100 deny   ip

access-list 100 deny   ip

access-list 100 deny   ip

access-list 100 deny   ip

access-list 100 deny   ip

access-list 100 deny   ip

access-list 100 deny   ip any

access-list 100 permit ip any any




5. Security Considerations:


Use of most of these special use prefixes open up significant opportunities

for anonymity and ambiguity. People, being what they are, will hide behind

ambiguous or nebulous identities to do things that are antisocial and

downright hostile. It would be nice to have better authentication methods

in play than an IP address which has lost its global uniqueness.


6. References:


[DHC-IPV4-AUTOCONFIG] - R. Troll, Automatically Choosing an IP Address

in an Ad-Hoc IPv4 Network, Internet draft,

draft-ietf-dhc-ipv4-autoconfig-04.txt, October 1998


[RFC1918]  Y. Rekhter, Address Allocation for Private Internets,

February 1996, RFC 1918


[RFC1122] R. Braden,  Requirements for Internet Hosts -- Communication Layers,

October 1989, RFC 1122


[RFC1166] S.Kirkpatrick, INTERNET NUMBERS, July 1990, RFC 1166


[RFC1812] F. Baker, Requirements for IP Version 4 Routers,

June 1995, RFC 1812


[RFC2267] P. Ferguson, D. Senie, Network Ingress Filtering:

Defeating Denial of Service Attacks which employ IP Source Address Spoofing,

January 1998, RFC 2267


[NET-TEST] Netname: IANA, Netnumber:, Coordinator:

Internet Assigned Numbers Authority, 1993


[LOOPBACK] Netname: LOOPBACK, Netnumber:, Coordinator:

Internet Assigned Numbers Authority, 1972


[RESERVED-1] Netname RESERVED-1, Netblock: -,

Coordinator: Internet Assigned Numbers Authority, 1972


8. Author's Address


      Bill Manning

      PO 12317

      Marina del Rey, CA. 90295




9.  Full Copyright Statement


   Copyright (C) Bill Manning (2001).  All Rights Reserved.


   This document and translations of it may be copied and furnished to

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   This document and the information contained herein is provided on an

   "AS IS" basis and the author DISCLAIMS ALL WARRANTIES,