Movatterモバイル変換

Internet Engineering Task Force (IETF)                        M. AndrewsRequest for Comments: 6303                                           ISCBCP: 163                                                       July 2011Category: Best Current PracticeISSN: 2070-1721Locally Served DNS ZonesAbstract   Experience with the Domain Name System (DNS) has shown that there are   a number of DNS zones that all iterative resolvers and recursive   nameservers should automatically serve, unless configured otherwise.RFC 4193 specifies that this should occur for D.F.IP6.ARPA.  This   document extends the practice to cover the IN-ADDR.ARPA zones forRFC1918 address space and other well-known zones with similar   characteristics.Status of This Memo   This memo documents an Internet Best Current Practice.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   BCPs is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6303.Copyright Notice   Copyright (c) 2011 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Andrews                   Best Current Practice                 [Page 1]

RFC 6303                Locally Served DNS Zones               July 2011   This document may contain material from IETF Documents or IETF   Contributions published or made publicly available before November   10, 2008.  The person(s) controlling the copyright in some of this   material may not have granted the IETF Trust the right to allow   modifications of such material outside the IETF Standards Process.   Without obtaining an adequate license from the person(s) controlling   the copyright in such materials, this document may not be modified   outside the IETF Standards Process, and derivative works of it may   not be created outside the IETF Standards Process, except to format   it for publication as an RFC or to translate it into languages other   than English.Table of Contents1. Introduction ....................................................21.1. Reserved Words .............................................32. Effects on Sites UsingRFC 1918 Addresses .......................33. Changes to Iterative Resolver Behaviour .........................44. Lists Of Zones Covered ..........................................54.1.RFC 1918 Zones .............................................54.2.RFC 5735 andRFC 5737 Zones ................................54.3. Local IPv6 Unicast Addresses ...............................64.4. IPv6 Locally Assigned Local Addresses ......................64.5. IPv6 Link-Local Addresses ..................................74.6. IPv6 Example Prefix ........................................75. Zones That Are Out of Scope .....................................76. IANA Considerations .............................................87. Security Considerations .........................................88. Acknowledgements ................................................99. References ......................................................99.1. Normative References .......................................99.2. Informative References ....................................101.  Introduction   Experience with the Domain Name System (DNS, [RFC1034] and [RFC1035])   has shown that there are a number of DNS zones that all iterative   resolvers and recursive nameservers SHOULD automatically serve,   unless intentionally configured otherwise.  These zones include, but   are not limited to, the IN-ADDR.ARPA zones for the address space   allocated by [RFC1918] and the IP6.ARPA zones for locally assigned   unique local IPv6 addresses defined in [RFC4193].Andrews                   Best Current Practice                 [Page 2]

RFC 6303                Locally Served DNS Zones               July 2011   This recommendation is made because data has shown that significant   leakage of queries for these namespaces is occurring, despite   instructions to restrict them, and because it has therefore become   necessary to deploy sacrificial nameservers to protect the immediate   parent nameservers for these zones from excessive, unintentional   query load [AS112] [RFC6304] [RFC6305].  There is every expectation   that the query load will continue to increase unless steps are taken   as outlined here.   Additionally, queries from clients behind badly configured firewalls   that allow outgoing queries for these namespaces, but drop the   responses, put a significant load on the root servers (forward zones   but not reverse zones are configured).  They also cause operational   load for the root server operators, as they have to reply to   enquiries about why the root servers are "attacking" these clients.   Changing the default configuration will address all these issues for   the zones listed inSection 4.   [RFC4193] recommends that queries for D.F.IP6.ARPA be handled   locally.  This document extends the recommendation to cover the   IN-ADDR.ARPA zones for [RFC1918] and other well-known IN-ADDR.ARPA   and IP6.ARPA zones for which queries should not appear on the public   Internet.   It is hoped that by doing this the number of sacrificial servers   [AS112] will not have to be increased, and may in time be reduced.   This recommendation should also help DNS responsiveness for sites   that are using [RFC1918] addresses but do not follow the last   paragraph inSection 3 of [RFC1918].1.1.  Reserved Words   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described in [RFC2119].2.  Effects on Sites UsingRFC 1918 Addresses   For most sites using [RFC1918] addresses, the changes here will have   little or no detrimental effect.  If the site does not already have   the reverse tree populated, the only effect will be that the name   error responses will be generated locally rather than remotely.   For sites that do have the reverse tree populated, most will either   have a local copy of the zones or will be forwarding the queries to   servers that have local copies of the zone.  Therefore, this   recommendation will not be relevant.Andrews                   Best Current Practice                 [Page 3]

RFC 6303                Locally Served DNS Zones               July 2011   The most significant impact will be felt at sites that make use of   delegations for [RFC1918] addresses and have populated these zones.   These sites will need to override the default configuration expressed   in this document to allow resolution to continue.  Typically, such   sites will be fully disconnected from the Internet and have their own   root servers for their own non-Internet DNS tree.3.  Changes to Iterative Resolver Behaviour   Unless configured otherwise, an iterative resolver will now return   authoritatively (AA=1) name errors (RCODE=3) for queries within the   zones inSection 4, with the obvious exception of queries for the   zone name itself where SOA, NS, and "no data" responses will be   returned as appropriate to the query type.  One common way to do this   all at once is to serve empty (SOA and NS only) zones.   An implementation of this recommendation MUST provide a mechanism to   disable this new behaviour, and SHOULD allow this decision on a zone-   by-zone basis.   If using empty zones one SHOULD NOT use the same NS and SOA records   as used on the public Internet servers, as that will make it harder   to detect the origin of the responses and thus any leakage to the   public Internet servers.  It is RECOMMENDED that the NS record   defaults to the name of the zone and the SOA MNAME defaults to the   name of the only NS RR's (Resource Record's) target.  The SOA RNAME   SHOULD default to "nobody.invalid."  [RFC2606].  Implementations   SHOULD provide a mechanism to set these values.  No address records   need to be provided for the nameserver.   Below is an example of a generic empty zone in master file format.   It will produce a negative cache Time to Live (TTL) of 3 hours.   @ 10800 IN SOA @ nobody.invalid. 1 3600 1200 604800 10800   @ 10800 IN NS @   The SOA RR is needed to support negative caching [RFC2308] of name   error responses and to point clients to the primary master for DNS   dynamic updates.   SOA values of particular importance are the MNAME, the SOA RR's TTL,   and the negTTL value.  Both TTL values SHOULD match.  The rest of the   SOA timer values MAY be chosen arbitrarily since they are not   intended to control any zone transfer activity.   The NS RR is needed as some UPDATE [RFC2136] clients use NS queries   to discover the zone to be updated.  Having no address records for   the nameserver is expected to abort UPDATE processing in the client.Andrews                   Best Current Practice                 [Page 4]

RFC 6303                Locally Served DNS Zones               July 20114.  Lists Of Zones Covered   The following subsections are the initial contents of the IANA   registry as described in the IANA Considerations section.  Following   the caveat in that section, the list contains only reverse zones   corresponding to permanently assigned address space.  The zone name   is the entity to be registered.4.1.RFC 1918 Zones   The following zones correspond to the IPv4 address space reserved in   [RFC1918].                         +----------------------+                         | Zone                 |                         +----------------------+                         | 10.IN-ADDR.ARPA      |                         | 16.172.IN-ADDR.ARPA  |                         | 17.172.IN-ADDR.ARPA  |                         | 18.172.IN-ADDR.ARPA  |                         | 19.172.IN-ADDR.ARPA  |                         | 20.172.IN-ADDR.ARPA  |                         | 21.172.IN-ADDR.ARPA  |                         | 22.172.IN-ADDR.ARPA  |                         | 23.172.IN-ADDR.ARPA  |                         | 24.172.IN-ADDR.ARPA  |                         | 25.172.IN-ADDR.ARPA  |                         | 26.172.IN-ADDR.ARPA  |                         | 27.172.IN-ADDR.ARPA  |                         | 28.172.IN-ADDR.ARPA  |                         | 29.172.IN-ADDR.ARPA  |                         | 30.172.IN-ADDR.ARPA  |                         | 31.172.IN-ADDR.ARPA  |                         | 168.192.IN-ADDR.ARPA |                         +----------------------+4.2.RFC 5735 andRFC 5737 Zones   The following zones correspond to those address ranges from [RFC5735]   and [RFC5737] that are not expected to appear as source or   destination addresses on the public Internet; as such, there are no   globally unique names associated with the addresses in these ranges.Andrews                   Best Current Practice                 [Page 5]

RFC 6303                Locally Served DNS Zones               July 2011   The recommendation to serve an empty zone 127.IN-ADDR.ARPA is not an   attempt to discourage any practice to provide a PTR RR for   1.0.0.127.IN-ADDR.ARPA locally.  In fact, a meaningful reverse   mapping should exist, but the exact setup is out of the scope of this   document.  Similar logic applies to the reverse mapping for ::1   (Section 4.3).  The recommendations made here simply assume that no   other coverage for these domains exists.         +------------------------------+-----------------------+         | Zone                         | Description           |         +------------------------------+-----------------------+         | 0.IN-ADDR.ARPA               | IPv4 "THIS" NETWORK   |         | 127.IN-ADDR.ARPA             | IPv4 Loopback NETWORK |         | 254.169.IN-ADDR.ARPA         | IPv4 LINK LOCAL       |         | 2.0.192.IN-ADDR.ARPA         | IPv4 TEST-NET-1       |         | 100.51.198.IN-ADDR.ARPA      | IPv4 TEST-NET-2       |         | 113.0.203.IN-ADDR.ARPA       | IPv4 TEST-NET-3       |         | 255.255.255.255.IN-ADDR.ARPA | IPv4 BROADCAST        |         +------------------------------+-----------------------+4.3.  Local IPv6 Unicast Addresses   The reverse mappings ([RFC3596], Section 2.5 ("IP6.ARPA Domain")) for   the IPv6 Unspecified (::) and Loopback (::1) addresses ([RFC4291],   Sections2.4,2.5.2, and2.5.3) are covered by these two zones:               +-------------------------------------------+               | Zone                                      |               +-------------------------------------------+               | 0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.\ |               |     0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA      |               | 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.\ |               |     0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA      |               +-------------------------------------------+   Note: Line breaks and escapes ('\') have been inserted above for   readability and to adhere to line width constraints.  They are not   parts of the zone names.4.4.  IPv6 Locally Assigned Local AddressesSection 4.4 of [RFC4193] already required special treatment of:                             +--------------+                             | Zone         |                             +--------------+                             | D.F.IP6.ARPA |                             +--------------+Andrews                   Best Current Practice                 [Page 6]

RFC 6303                Locally Served DNS Zones               July 20114.5.  IPv6 Link-Local Addresses   IPv6 Link-Local Addresses as described in[RFC4291], Section 2.5.6   are covered by four distinct reverse DNS zones:                            +----------------+                            | Zone           |                            +----------------+                            | 8.E.F.IP6.ARPA |                            | 9.E.F.IP6.ARPA |                            | A.E.F.IP6.ARPA |                            | B.E.F.IP6.ARPA |                            +----------------+4.6.  IPv6 Example Prefix   IPv6 example prefix [RFC3849].                       +--------------------------+                       | Zone                     |                       +--------------------------+                       | 8.B.D.0.1.0.0.2.IP6.ARPA |                       +--------------------------+   Note: 8.B.D.0.1.0.0.2.IP6.ARPA is not being used as an example here.5.  Zones That Are Out of Scope   IPv6 site-local addresses (deprecated, see [RFC4291] Sections2.4 and   2.5.7), and IPv6 non-locally assigned local addresses ([RFC4193]) are   not covered here.   It is expected that IPv6 site-local addresses will be self correcting   as IPv6 implementations remove support for site-local addresses.   However, sacrificial servers for the zones C.E.F.IP6.ARPA through   F.E.F.IP6.ARPA may still need to be deployed in the short term if the   traffic becomes excessive.   For IPv6 non-locally assigned local addresses (L = 0) [RFC4193],   there has been no decision made about whether the Regional Internet   Registries (RIRs) will provide delegations in this space or not.  If   they don't, then C.F.IP6.ARPA will need to be added to the list inSection 4.4.  If they do, then registries will need to take steps to   ensure that nameservers are provided for these addresses.Andrews                   Best Current Practice                 [Page 7]

RFC 6303                Locally Served DNS Zones               July 2011   IP6.INT was once used to provide reverse mapping for IPv6.  IP6.INT   was deprecated in [RFC4159] and the delegation removed from the INT   zone in June 2006.  While it is possible that legacy software   continues to send queries for names under the IP6.INT domain, this   document does not specify that IP6.INT be considered a local zone.   This document has also deliberately ignored names immediately under   the root domain.  While there is a subset of queries to the root   nameservers that could be addressed using the techniques described   here (e.g., .local, .workgroup, and IPv4 addresses), there is also a   vast amount of traffic that requires a different strategy (e.g.,   lookups for unqualified hostnames, IPv6 addresses).6.  IANA Considerations   IANA has established a registry of zones that require this default   behaviour.  The initial contents of this registry are defined inSection 4.  Implementors are encouraged to periodically check this   registry and adjust their implementations to reflect changes therein.   This registry can be amended through "IETF Review" as per [RFC5226].   As part of this review process, it should be noted that once a zone   is added it is effectively added permanently; once an address range   starts being configured as a local zone in systems on the Internet,   it will be impossible to reverse those changes.   IANA should coordinate with the RIRs to ensure that, as DNS Security   (DNSSEC) is deployed in the reverse tree, delegations for these zones   are made in the manner described inSection 7.7.  Security Considerations   During the initial deployment phase, particularly where [RFC1918]   addresses are in use, there may be some clients that unexpectedly   receive a name error rather than a PTR record.  This may cause some   service disruption until their recursive nameserver(s) have been   re-configured.   As DNSSEC is deployed within the IN-ADDR.ARPA and IP6.ARPA   namespaces, the zones listed above will need to be delegated as   insecure delegations, or be within insecure zones.  This will allow   DNSSEC validation to succeed for queries in these spaces despite not   being answered from the delegated servers.   It is recommended that sites actively using these namespaces secure   them using DNSSEC [RFC4035] by publishing and using DNSSEC trust   anchors.  This will protect the clients from accidental import of   unsigned responses from the Internet.Andrews                   Best Current Practice                 [Page 8]

RFC 6303                Locally Served DNS Zones               July 20118.  Acknowledgements   This work was supported by the US National Science Foundation   (research grant SCI-0427144) and DNS-OARC.9.  References9.1.  Normative References   [RFC1034]  Mockapetris, P., "DOMAIN NAMES - CONCEPTS AND FACILITIES",              STD 13,RFC 1034, November 1987.   [RFC1035]  Mockapetris, P., "DOMAIN NAMES - IMPLEMENTATION AND              SPECIFICATION", STD 13,RFC 1035, November 1987.   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,              and E. Lear, "Address Allocation for Private Internets",BCP 5,RFC 1918, February 1996.   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2136]  Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,              "Dynamic Updates in the Domain Name System (DNS UPDATE)",RFC 2136, April 1997.   [RFC2308]  Andrews, M., "Negative Caching of DNS Queries (DNS              NCACHE)",RFC 2308, March 1998.   [RFC2606]  Eastlake 3rd, D. and A. Panitz, "Reserved Top Level DNS              Names",BCP 32,RFC 2606, June 1999.   [RFC3596]  Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,              "DNS Extensions to Support IP Version 6",RFC 3596,              October 2003.   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.              Rose, "Protocol Modifications for the DNS Security              Extensions",RFC 4035, March 2005.   [RFC4159]  Huston, G., "Deprecation of "ip6.int"",BCP 109,RFC 4159,              August 2005.   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast              Addresses",RFC 4193, October 2005.Andrews                   Best Current Practice                 [Page 9]

RFC 6303                Locally Served DNS Zones               July 2011   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing              Architecture",RFC 4291, February 2006.   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an              IANA Considerations Section in RFCs",BCP 26,RFC 5226,              May 2008.9.2.  Informative References   [AS112]    "AS112 Project", <http://www.as112.net/>.   [RFC3849]  Huston, G., Lord, A., and P. Smith, "IPv6 Address Prefix              Reserved for Documentation",RFC 3849, July 2004.   [RFC5735]  Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses",BCP 153,RFC 5735, January 2010.   [RFC5737]  Arkko, J., Cotton, M., and L. Vegoda, "IPv4 Address Blocks              Reserved for Documentation",RFC 5737, January 2010.   [RFC6304]  Abley, J. and W. Maton, "AS112 Nameserver Operations",RFC 6304, July 2011.   [RFC6305]  Abley, J. and W. Maton, "I'm Being Attacked by              PRISONER.IANA.ORG!",RFC 6305, July 2011.Author's Address   Mark P. Andrews   Internet Systems Consortium   950 Charter Street   Redwood City, CA  94063   US   EMail: marka@isc.orgAndrews                   Best Current Practice                [Page 10]