RFC 6303
Locally Served DNS Zones
RFC 6303: Locally Served DNS Zones 🦋
Okay bestie, this is RFC 6303, titled Locally Served DNS Zones ✨. M. Andrews from ISC wrote it 💅, it's a Best Current Practice (BCP 163 🎀), and it came out in July 2011. It's an IETF document with ISSN 2070-1721. The header doesn't list anything it obsoletes or updates 🙈.
Abstract 🌸
Okay so DNS experience has shown that there's a bunch of DNS zones that every iterative resolver and recursive nameserver should automatically serve, unless somebody configures it otherwise 💅. RFC 4193 says this should happen for D.F.IP6.ARPA. This doc extends the practice to the IN-ADDR.ARPA zones for RFC 1918 address space, plus other well-known zones with similar vibes ✨.
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 went through public review and got approved for publication by the Internet Engineering Steering Group (IESG). More info on BCPs is in Section 2 of RFC 5741.
For the current status, any errata, and how to send feedback, check 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 read these carefully, because they spell out your rights and restrictions for this document. Code Components pulled out of this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions, and they come without warranty as described in the Simplified BSD License 🫶.
This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The people who control the copyright in some of that material may not have granted the IETF Trust the right to allow modifications outside the IETF Standards Process. So unless you get an adequate license from those copyright holders, 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. The exceptions are formatting it for publication as an RFC or translating 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 ....................................101. Introduction ✨
Okay so DNS experience (DNS, [RFC1034] and [RFC1035]) has shown that there are a bunch of DNS zones that all iterative resolvers and recursive nameservers SHOULD automatically serve, unless somebody intentionally configures them otherwise 💖. These include, but aren't 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].
Why? Because data shows there's a lot of leakage of queries for these namespaces, even though people were told to restrict them 😭. That made it necessary to deploy sacrificial nameservers to protect the immediate parent nameservers for these zones from excessive, unintentional query load [AS112] [RFC6304] [RFC6305]. The query load is expected to keep climbing unless steps are taken as outlined here 📈.
Also, clients behind badly configured firewalls allow outgoing queries for these namespaces but drop the responses, and that puts a serious load on the root servers (forward zones but not reverse zones are configured) 💀. It also creates operational load for the root server operators, who have to answer questions about why the root servers are "attacking" these clients 🙈. Changing the default configuration will address all of these issues for the zones listed in Section 4 🎀.
[RFC4193] recommends that queries for D.F.IP6.ARPA be handled locally. This document extends that 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 🌸.
The hope is that doing this means the number of sacrificial servers [AS112] won't have to increase, and might even go down over time 🧚.
This recommendation should also help DNS responsiveness for sites that use [RFC1918] addresses but don't 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 doesn't already have the reverse tree populated, the only effect is that name error responses get generated locally instead of remotely 🙌.
For sites that do have the reverse tree populated, most will either have a local copy of the zones or forward the queries to servers that have local copies of the zone. So this recommendation won't be relevant for them 😌.
The biggest impact is felt at sites that use delegations for [RFC1918] addresses and have populated these zones 😬. These sites will need to override the default configuration expressed in this document to keep resolution working. Typically, such sites are 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 💅. The obvious exception is queries for the zone name itself, where SOA, NS, and "no data" responses get returned as appropriate to the query type. One common way to do all of this at once is to serve empty zones (SOA and NS only) ✨.
An implementation of this recommendation MUST provide a mechanism to disable this new behaviour, and SHOULD allow that decision on a zone-by-zone basis 🔧.
If you're using empty zones, you SHOULD NOT use the same NS and SOA records as the public Internet servers 🙈. Doing that would make it harder to detect where the responses came from, and so any leakage to the public Internet servers would be harder to catch. It is RECOMMENDED that the NS record defaults to the name of the zone, and that 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 🫶.
Here's 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 because 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 🚫.
4. Lists Of Zones Covered 👑
The following subsections are the initial contents of the IANA registry 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 🌸
okay so these zones line up with the address ranges from [RFC5735] and [RFC5737] that aren't supposed to show up as source or destination addresses on the public Internet 🙈 which means there are no globally unique names for them. not one. iconic behaviour from the addresses honestly 💅
the recommendation to serve an empty zone 127.IN-ADDR.ARPA is NOT trying to stop anyone from making a PTR record for 1.0.0.127.IN-ADDR.ARPA locally 🫶 a meaningful reverse mapping should totally exist, but how you set that up is out of scope for this document ✨ the same logic goes for the reverse mapping for ::1 (Section 4.3). bestie, these recommendations just assume that nobody else is already covering these domains 🦋
+------------------------------+-----------------------+
| 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 🎀
okay so Section 4.4 of [RFC4193] already required special treatment of the following 🫶
+--------------+
| Zone |
+--------------+
| D.F.IP6.ARPA |
+--------------+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's 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 🫶
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 🌸 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), but 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 🫶
bestie, this one is serious: once a zone is in, it's in forever. no take-backsies 💀
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 🛡️✨
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.
[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📦 where this page comes from
- ietf: rfc6303 2011-07
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