e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsINTERNET-DRAFT D. Senie
e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsCategory: BCP Amaranth Networks Inc.
e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsExpires in six months July 2005
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Encouraging the use of DNS IN-ADDR Mapping
e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsStatus of this Memo
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews By submitting this Internet-Draft, each author represents that any
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews applicable patent or other IPR claims of which he or she is aware
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews have been or will be disclosed, and any of which he or she becomes
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews aware will be disclosed, in accordance with Section 6 of BCP 79.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Internet-Drafts are working documents of the Internet Engineering
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Task Force (IETF), its areas, and its working groups. Note that
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews other groups may also distribute working documents as Internet-
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Internet-Drafts are draft documents valid for a maximum of six months
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews and may be updated, replaced, or obsoleted by other documents at any
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews time. It is inappropriate to use Internet-Drafts as reference
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews material or to cite them other than as "work in progress."
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews The list of current Internet-Drafts can be accessed at
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews The list of Internet-Draft Shadow Directories can be accessed at
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Mapping of addresses to names has been a feature of DNS. Many sites,
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews implement it, many others don't. Some applications attempt to use it
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews as a part of a security strategy. The goal of this document is to
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews encourage proper deployment of address to name mappings, and provide
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews guidance for their use.
e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsCopyright Notice
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Copyright (C) The Internet Society. (2005)
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews1. Introduction
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews The Domain Name Service has provision for providing mapping of IP
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews addresses to host names. It is common practice to ensure both name to
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews address, and address to name mappings are provided for networks. This
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews practice, while documented, has never been required, though it is
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews generally encouraged. This document both encourages the presence of
e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsSenie [Page 1]
e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsInternet-Draft Encouraging the use of DNS IN-ADDR Mapping July 2005
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews these mappings and discourages reliance on such mappings for security
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews document are to be interpreted as described in RFC 2119 [RFC2119].
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews2. Discussion
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews From the early days of the Domain Name Service [RFC883] a special
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews domain has been set aside for resolving mappings of IP addresses to
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews domain names. This was refined in [RFC1035], describing the .IN-
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews ADDR.ARPA in use today. For the in the IPv6 address space, .IP6.ARPA
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews was added [RFC3152]. This document uses IPv4 CIDR block sizes and
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews allocation strategy where there are differences and uses IPv4
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews terminology. Aside from these differences, this document can and
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews should be applied to both address spaces.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews The assignment of blocks of IP address space was delegated to three
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews regional registries. Guidelines for the registries are specified in
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews [RFC2050], which requires regional registries to maintain IN-ADDR
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews records on the large blocks of space issued to ISPs and others.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews ARIN's policy requires ISPs to maintain IN-ADDR for /16 or larger
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews allocations. For smaller allocations, ARIN can provide IN-ADDR for
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews /24 and shorter prefixes. [ARIN]. APNIC provides methods for ISPs to
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews update IN-ADDR, however the present version of its policy document
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews for IPv4 [APNIC] dropped the IN-ADDR requirements that were in draft
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews copies of this document. As of this writing, it appears APNIC has no
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews actual policy on IN-ADDR. RIPE appears to have the strongest policy
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews in this area [RIPE302] indicating Local Internet Registries should
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews provide IN-ADDR services, and delegate those as appropriate when
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews address blocks are delegated.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews As we can see, the regional registries have their own policies for
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews recommendations and/or requirements for IN-ADDR maintenance. It
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews should be noted, however, that many address blocks were allocated
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews before the creation of the regional registries, and thus it is
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews unclear whether any of the policies of the registries are binding on
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews those who hold blocks from that era.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Registries allocate address blocks on CIDR [RFC1519] boundaries.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Unfortunately the IN-ADDR zones are based on classful allocations.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Guidelines [RFC2317] for delegating on non-octet-aligned boundaries
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews exist, but are not always implemented.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews3. Examples of impact of missing IN-ADDR
e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsSenie [Page 2]
e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsInternet-Draft Encouraging the use of DNS IN-ADDR Mapping July 2005
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews These are some examples of problems that may be introduced by
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews reliance on IN-ADDR.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Some applications use DNS lookups for security checks. To ensure
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews validity of claimed names, some applications will look up IN-ADDR
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews records to get names, and then look up the resultant name to see if
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews it maps back to the address originally known. Failure to resolve
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews matching names is seen as a potential security concern.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Some FTP sites will flat-out reject users, even for anonymous FTP, if
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews the IN-ADDR lookup fails or if the result of the IN-ADDR lookup when
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews itself resolved, does not match. Some Telnet servers also implement
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Web sites are in some cases using IN-ADDR checks to verify whether
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews the client is located within a certain geopolitical entity. This
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews approach has been employed for downloads of crypto software, for
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews example, where export of that software is prohibited to some locales.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Credit card anti-fraud systems also use these methods for geographic
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews placement purposes.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews The popular TCP Wrappers program found on most Unix and Linux systems
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews has options to enforce IN-ADDR checks and to reject any client that
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews does not resolve. This program also has a way to check to see that
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews the name given by a PTR record then resolves back to the same IP
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews address. This method provdes more comfort but no appreciable
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews additional security.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Some anti-spam (anti junk email) systems use IN-ADDR to verify the
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews presence of a PTR record, or validate the PTR value points back to
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews the same address.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Many web servers look up the IN-ADDR of visitors to be used in log
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews analysis. This adds to the server load, but in the case of IN-ADDR
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews unavailability, it can lead to delayed responses for users.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Traceroutes with descriptive IN-ADDR naming proves useful when
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews debugging problems spanning large areas. When this information is
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews missing, the traceroutes take longer, and it takes additional steps
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews to determine that network is the cause of problems.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Wider-scale implementation of IN-ADDR on dialup, wireless access and
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews other such client-oriented portions of the Internet would result in
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews lower latency for queries (due to lack of negative caching), and
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews lower name server load and DNS traffic.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews4. Recommendations
e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsSenie [Page 3]
e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsInternet-Draft Encouraging the use of DNS IN-ADDR Mapping July 2005
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews 4.1 Delegation Recommendations
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Regional Registries and any Local Registries to whom they delegate
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews should establish and convey a policy to those to whom they delegate
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews blocks that IN-ADDR mappings are recommended. Policies should
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews recommend those receiving delegations to provide IN-ADDR service
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews and/or delegate to downstream customers.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Network operators should define and implement policies and procedures
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews which delegate IN-ADDR to their clients who wish to run their own IN-
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews ADDR DNS services, and provide IN-ADDR services for those who do not
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews have the resources to do it themselves. Delegation mechanisms should
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews permit the downstream customer to implement and comply with IETF
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews recommendations application of IN-ADDR to CIDR [RFC2317].
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews All IP address space assigned and in use should be resolved by IN-
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews ADDR records. All PTR records must use canonical names.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews All IP addresses in use within a block should have an IN-ADDR
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews mapping. Those addresses not in use, and those that are not valid for
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews use (zeros or ones broadcast addresses within a CIDR block) need not
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews have mappings.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews It should be noted that due to CIDR, many addresses that appear to be
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews otherwise valid host addresses may actually be zeroes or ones
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews broadcast addresses. As such, attempting to audit a site's degree of
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews compliance may only be done with knowledge of the internal subnet
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews architecture of the site. It can be assumed, however, any host that
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews originates an IP packet necessarily will have a valid host address,
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews and must therefore have an IN-ADDR mapping.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews4.2 Application Recommendations
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Applications SHOULD NOT rely on IN-ADDR for proper operation. The use
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews of IN-ADDR, sometimes in conjunction with a lookup of the name
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews resulting from the PTR record provides no real security, can lead to
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews erroneous results and generally just increases load on DNS servers.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Further, in cases where address block holders fail to properly
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews configure IN-ADDR, users of those blocks are penalized.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews5. Security Considerations
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews This document has no negative impact on security. While it could be
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews argued that lack of PTR record capabilities provides a degree of
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews anonymity, this is really not valid. Trace routes, whois lookups and
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews other sources will still provide methods for discovering identity.
e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsSenie [Page 4]
e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsInternet-Draft Encouraging the use of DNS IN-ADDR Mapping July 2005
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews By recommending applications avoid using IN-ADDR as a security
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews mechanism this document points out that this practice, despite its
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews use by many applications, is an ineffective form of security.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Applications should use better mechanisms of authentication.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews6. IANA Considerations
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews There are no IANA considerations for this document.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews7. References
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews7.1 Normative References
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews [RFC883] P.V. Mockapetris, "Domain names: Implementation
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews specification," RFC883, November 1983.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews [RFC1035] P.V. Mockapetris, "Domain Names: Implementation
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Specification," RFC 1035, November 1987.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews [RFC1519] V. Fuller, et. al., "Classless Inter-Domain Routing (CIDR):
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews an Address Assignment and Aggregation Strategy," RFC 1519, September
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews [RFC2026] S. Bradner, "The Internet Standards Process -- Revision 3",
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews RFC 2026, BCP 9, October 1996.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Requirement Levels", RFC 2119, BCP 14, March 1997.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews [RFC2050] K. Hubbard, et. al., "Internet Registry IP Allocation
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Guidelines", RFC2050, BCP 12, Novebmer 1996.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews [RFC2317] H. Eidnes, et. al., "Classless IN-ADDR.ARPA delegation,"
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews RFC 2317, March 1998.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews [RFC3152] R. Bush, "Delegation of IP6.ARPA," RFC 3152, BCP 49, August
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews7.2 Informative References
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews [ARIN] "ISP Guidelines for Requesting Initial IP Address Space," date
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews unknown, http://www.arin.net/regserv/initial-isp.html
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews [APNIC] "Policies For IPv4 Address Space Management in the Asia
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Pacific Region," APNIC-086, 13 January 2003.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews [RIPE302] "Policy for Reverse Address Delegation of IPv4 and IPv6
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Address Space in the RIPE NCC Service Region", RIPE-302, April 26,
e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsSenie [Page 5]
e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsInternet-Draft Encouraging the use of DNS IN-ADDR Mapping July 2005
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews 2004. http://www.ripe.net//ripe/docs/rev-del.html
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews8. Acknowledgements
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Thanks to Peter Koch and Gary Miller for their input, and to many
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews people who encouraged me to write this document.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews9. Author's Address
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Daniel Senie
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Amaranth Networks Inc.
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews 324 Still River Road
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Bolton, MA 01740
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Phone: (978) 779-5100
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews EMail: dts@senie.com
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews10. Full Copyright Statement
e3c0f34cba09741486b31db3814fc3a26227547bMark Andrews Copyright (C) The Internet Society (2005).
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e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsSenie [Page 6]
e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsInternet-Draft Encouraging the use of DNS IN-ADDR Mapping July 2005
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e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsAcknowledgement
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e3c0f34cba09741486b31db3814fc3a26227547bMark AndrewsSenie [Page 7]