a bit late but here is #2 ---------------------------------------------------- INTERNET-DRAFT draft-manning-dsua-02.txt Bill Manning ISI 17 April 2000 Documenting Special Use IPv4 Address Blocks that have been registered with IANA 1. Status of this Memo This draft, file name draft-manning-dsua-02.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. 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 http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 2. PREAMBLE: 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 reserved for future delegation in the operational Internet. The current list of special use prefixes: 0.0.0.0/8 127.0.0.0/8 192.0.2.0/24 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 169.254.0.0/16 all D/E space 2.1 Prefix Discussion: 0.0.0.0/8 has a number of unique properties, many of which were built into the protocol stacks used throughout the Internet. 0.0.0.0/32 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 0.0.0.0 to encode the idea of "default". Also, many stacks will allow the system administrator to encode IP addresses of the form 0.0.160.57, 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 0.0.0.0/8 as a special use net-block. Router and Host requirements documents and implementations treat this range with special use constraints. 127.0.0.0/8 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, 127.0.0.1/32 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. 192.0.2.0/24 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 example.com or example.net in vendor and protocol documentation. 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 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. 169.254.0.0/16 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 RIP. 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. 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 192.0.0.0/24 and the specific address that they use is 192.0.0.192/32. 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 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. 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 designation, just not as a source). An example of one form of access control is listed below: ... access-list 100 deny ip host 0.0.0.0 any access-list 100 deny ip 127.0.0.0 0.255.255.255 255.0.0.0 0.255.255.255 access-list 100 deny ip 10.0.0.0 0.255.255.255 255.0.0.0 0.255.255.255 access-list 100 deny ip 172.16.0.0 0.15.255.255 255.240.0.0 0.15.255.255 access-list 100 deny ip 192.168.0.0 0.0.255.255 255.255.0.0 0.0.255.255 access-list 100 deny ip 192.0.2.0 0.0.0.255 255.255.255.0 0.0.0.255 access-list 100 deny ip 169.254.0.0 0.0.255.255 255.255.0.0 0.0.255.255 access-list 100 deny ip 240.0.0.0 7.255.255.255 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 et.al., 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 et.al, 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: 192.0.2.0, Coordinator: Internet Assigned Numbers Authority, 1993 [LOOPBACK] Netname: LOOPBACK, Netnumber: 127.0.0.0, Coordinator: Internet Assigned Numbers Authority, 1972 [RESERVED-1] Netname RESERVED-1, Netblock: 0.0.0.0 - 0.255.255.255, Coordinator: Internet Assigned Numbers Authority, 1972 8. Author's Address Bill Manning USC/ISI 4676 Admiralty Way, #1001 Marina del Rey, CA. 90292 USA bmanning@isi.edu 310.822.1511 -- "When in doubt, Twirl..." -anon