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rfc:rfc6303

Internet Engineering Task Force (IETF) M. Andrews Request for Comments: 6303 ISC BCP: 163 July 2011 Category: Best Current Practice ISSN: 2070-1721

                      Locally Served DNS Zones

Abstract

 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 for RFC
 1918 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 in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://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 to BCP 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 Contents

 1. Introduction ....................................................2
    1.1. Reserved Words .............................................3
 2. Effects on Sites Using RFC 1918 Addresses .......................3
 3. Changes to Iterative Resolver Behaviour .........................4
 4. Lists Of Zones Covered ..........................................5
    4.1. RFC 1918 Zones .............................................5
    4.2. RFC 5735 and RFC 5737 Zones ................................5
    4.3. Local IPv6 Unicast Addresses ...............................6
    4.4. IPv6 Locally Assigned Local Addresses ......................6
    4.5. IPv6 Link-Local Addresses ..................................7
    4.6. IPv6 Example Prefix ........................................7
 5. Zones That Are Out of Scope .....................................7
 6. IANA Considerations .............................................8
 7. Security Considerations .........................................8
 8. Acknowledgements ................................................9
 9. References ......................................................9
    9.1. Normative References .......................................9
    9.2. Informative References ....................................10

1. 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 in Section 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 in Section 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 Using RFC 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 in Section 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 2011

4. 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 and RFC 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],
 Sections 2.4, 2.5.2, and 2.5.3) 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 Addresses

 Section 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 2011

4.5. 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] Sections 2.4 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 in
 Section 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 in
 Section 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 in Section 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 2011

8. Acknowledgements

 This work was supported by the US National Science Foundation
 (research grant SCI-0427144) and DNS-OARC.

9. References

9.1. 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.org

Andrews Best Current Practice [Page 10]

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