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DNSEXT Working Group M. Graff
Internet-Draft P. Vixie
Obsoletes: 2671 (if approved) Internet Systems Consortium
Intended status: Standards Track July 28, 2009
Expires: January 29, 2010
Extension Mechanisms for DNS (EDNS0)
draft-ietf-dnsext-rfc2671bis-edns0-02
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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.
This Internet-Draft will expire on January 29, 2010.
Copyright Notice
Copyright (c) 2009 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 in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Abstract
The Domain Name System's wire protocol includes a number of fixed
fields whose range has been or soon will be exhausted and does not
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allow requestors to advertise their capabilities to responders. This
document describes backward compatible mechanisms for allowing the
protocol to grow.
This document updates the EDNS0 specification based on 10 years of
operational experience.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. EDNS Support Requirement . . . . . . . . . . . . . . . . . . . 3
4. Affected Protocol Elements . . . . . . . . . . . . . . . . . . 3
4.1. Message Header . . . . . . . . . . . . . . . . . . . . . . 3
4.2. Label Types . . . . . . . . . . . . . . . . . . . . . . . 4
4.3. UDP Message Size . . . . . . . . . . . . . . . . . . . . . 4
5. Extended Label Types . . . . . . . . . . . . . . . . . . . . . 4
6. OPT pseudo-RR . . . . . . . . . . . . . . . . . . . . . . . . 4
6.1. OPT Record Behavior . . . . . . . . . . . . . . . . . . . 4
6.2. OPT Record Format . . . . . . . . . . . . . . . . . . . . 5
6.3. Requestor's Payload Size . . . . . . . . . . . . . . . . . 6
6.4. Responder's Payload Size . . . . . . . . . . . . . . . . . 6
6.5. Payload Size Selection . . . . . . . . . . . . . . . . . . 7
6.6. Middleware Boxes . . . . . . . . . . . . . . . . . . . . . 7
6.7. Extended RCODE . . . . . . . . . . . . . . . . . . . . . . 7
6.8. OPT Options Type Allocation Procedure . . . . . . . . . . 8
7. Transport Considerations . . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1. Normative References . . . . . . . . . . . . . . . . . . . 10
11.2. Informative References . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
DNS [RFC1035] specifies a Message Format and within such messages
there are standard formats for encoding options, errors, and name
compression. The maximum allowable size of a DNS Message is fixed.
Many of DNS's protocol limits are too small for uses which are or
which are desired to become common. There is no way for
implementations to advertise their capabilities.
Unextended agents will not know how to interpret the protocol
extensions detailed here. In practice, these clients will be
upgraded when they have need of a new feature, and only new features
will make use of the extensions. Extended agents must be prepared
for behaviour of unextended clients in the face of new protocol
elements, and fall back gracefully to unextended DNS. [RFC2671]
originally proposed extensions to the basic DNS protocol to overcome
these deficiencies. This memo refines that specification and
obsoletes [RFC2671].
2. Requirements Language
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 RFC 2119 [RFC2119].
3. EDNS Support Requirement
EDNS support is manditory in a modern world. DNSSEC requires EDNS
support, and many other featres are made possible only by EDNS
support to request or advertise them.
4. Affected Protocol Elements
4.1. Message Header
The DNS Message Header's (see , section 4.1.1 [RFC1035]) second full
16-bit word is divided into a 4-bit OPCODE, a 4-bit RCODE, and a
number of 1-bit flags. The original reserved Z bits have been
allocated to various purposes, and most of the RCODE values are now
in use. More flags and more possible RCODEs are needed. The OPT
pseudo-RR specified below contains subfields that carry a bit field
extension of the RCODE field and additional flag bits, respectively.
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4.2. Label Types
The first two bits of a wire format domain label are used to denote
the type of the label. ,section 4.1.4 [RFC1035] allocates two of the
four possible types and reserves the other two. More label types
were proposed in [RFC2671] section 3.
4.3. UDP Message Size
DNS Messages are limited to 512 octets in size when sent over UDP.
While the minimum maximum reassembly buffer size still allows a limit
of 512 octets of UDP payload, most of the hosts now connected to the
Internet are able to reassemble larger datagrams. Some mechanism
must be created to allow requestors to advertise larger buffer sizes
to responders. To this end, the OPT pseudo-RR specified below
contains a maximum payload size field.
5. Extended Label Types
The first octet in the on-the-wire representation of a DNS label
specifies the label type; the basic DNS specification [RFC1035]
dedicates the two most significant bits of that octet for this
purpose.
This document reserves DNS label type 0b01 for use as an indication
for Extended Label Types. A specific extended label type is selected
by the 6 least significant bits of the first octet. Thus, Extended
Label Types are indicated by the values 64-127 (0b01xxxxxx) in the
first octet of the label.
This document does not describe any specific Extended Label Type.
In practice, Extended Label Types are difficult to use due to support
in clients and intermediate gateways. Therefore, the registry of
Extended Label Types is requested to be closed. They cause
interoperability problems and at present no defined label types are
in use.
6. OPT pseudo-RR
6.1. OPT Record Behavior
One OPT pseudo-RR (RR type 41) MAY be added to the additional data
section of a request. If present in requests, compliant responders
which implement EDNS MUST include an OPT record in non-truncated
responses, and SHOULD attempt to include them in all responses. An
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OPT is called a pseudo-RR because it pertains to a particular
transport level message and not to any actual DNS data. OPT RRs MUST
NOT be cached, forwarded, or stored in or loaded from master files.
The quantity of OPT pseudo-RRs per message MUST be either zero or
one, but not greater.
6.2. OPT Record Format
An OPT RR has a fixed part and a variable set of options expressed as
{attribute, value} pairs. The fixed part holds some DNS meta data
and also a small collection of basic extension elements which we
expect to be so popular that it would be a waste of wire space to
encode them as {attribute, value} pairs.
The fixed part of an OPT RR is structured as follows:
+------------+--------------+------------------------------+
| Field Name | Field Type | Description |
+------------+--------------+------------------------------+
| NAME | domain name | empty (root domain) |
| TYPE | u_int16_t | OPT |
| CLASS | u_int16_t | requestor's UDP payload size |
| TTL | u_int32_t | extended RCODE and flags |
| RDLEN | u_int16_t | describes RDATA |
| RDATA | octet stream | {attribute,value} pairs |
+------------+--------------+------------------------------+
OPT RR Format
The variable part of an OPT RR is encoded in its RDATA and is
structured as zero or more of the following:
+0 (MSB) +1 (LSB)
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | OPTION-CODE |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | OPTION-LENGTH |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: | |
/ OPTION-DATA /
/ /
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
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OPTION-CODE
Assigned by Expert Review.
OPTION-LENGTH
Size (in octets) of OPTION-DATA.
OPTION-DATA
Varies per OPTION-CODE.
Order of appearance of option tuples is never relevant. Any option
whose meaning is affected by other options is so affected no matter
which one comes first in the OPT RDATA.
Any OPTION-CODE values not understood by a responder or requestor
MUST be ignored. Specifications of such options might wish to
include some kind of signalled acknowledgement. For example, an
option specification might say that if a responder sees option XYZ,
it SHOULD include option XYZ in its response.
6.3. Requestor's Payload Size
The requestor's UDP payload size (which OPT stores in the RR CLASS
field) is the number of octets of the largest UDP payload that can be
reassembled and delivered in the requestor's network stack. Note
that path MTU, with or without fragmentation, may be smaller than
this. Values lower than 512 MUST be treated as equal to 512.
Note that a 512-octet UDP payload requires a 576-octet IP reassembly
buffer. Choosing 1280 for IPv4 over Ethernet would be reasonable.
The consequence of choosing too large a value may be an ICMP message
from an intermediate gateway, or even a silent drop of the response
message.
The requestor's maximum payload size can change over time, and MUST
therefore not be cached for use beyond the transaction in which it is
advertised.
6.4. Responder's Payload Size
The responder's maximum payload size can change over time, but can be
reasonably expected to remain constant between two sequential
transactions; for example, a meaningless QUERY to discover a
responder's maximum UDP payload size, followed immediately by an
UPDATE which takes advantage of this size. (This is considered
preferrable to the outright use of TCP for oversized requests, if
there is any reason to suspect that the responder implements EDNS,
and if a request will not fit in the default 512 payload size limit.)
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6.5. Payload Size Selection
Due to transaction overhead, it is unwise to advertise an
architectural limit as a maximum UDP payload size. Just because your
stack can reassemble 64KB datagrams, don't assume that you want to
spend more than about 4KB of state memory per ongoing transaction.
A requestor MAY choose to implement a fallback to smaller advertised
sizes to work around firewall or other network limitations. A
requestor SHOULD choose to use a fallback mechanism which begins with
a large size, such as 4096. If that fails, a fallback around the
1220 byte range SHOULD be tried, as it has a reasonable chance to fit
within a single Ethernet frame. Failing that, a requestor MAY choose
a 512 byte packet, which with large answers may cause a TCP retry.
6.6. Middleware Boxes
Middleware boxes MUST NOT limit DNS messages over UDP to 512 bytes.
Middleware boxes which simply forward requests to a recursive
resolver MUST NOT modify the OPT record contents in either direction.
6.7. Extended RCODE
The extended RCODE and flags (which OPT stores in the RR TTL field)
are structured as follows:
+0 (MSB) +1 (LSB)
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: | EXTENDED-RCODE | VERSION |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: | DO| Z |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
EXTENDED-RCODE
Forms upper 8 bits of extended 12-bit RCODE. Note that
EXTENDED-RCODE value "0" indicates that an unextended RCODE is
in use (values "0" through "15").
VERSION
Indicates the implementation level of whoever sets it. Full
conformance with this specification is indicated by version
``0.'' Requestors are encouraged to set this to the lowest
implemented level capable of expressing a transaction, to
minimize the responder and network load of discovering the
greatest common implementation level between requestor and
responder. A requestor's version numbering strategy MAY
ideally be a run time configuration option.
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If a responder does not implement the VERSION level of the
request, then it answers with RCODE=BADVERS. All responses
MUST be limited in format to the VERSION level of the request,
but the VERSION of each response SHOULD be the highest
implementation level of the responder. In this way a requestor
will learn the implementation level of a responder as a side
effect of every response, including error responses and
including RCODE=BADVERS.
DO
DNSSEC OK bit as defined by [RFC3225].
Z
Set to zero by senders and ignored by receivers, unless
modified in a subsequent specification.
6.8. OPT Options Type Allocation Procedure
Allocations assigned by expert review. TBD
7. Transport Considerations
The presence of an OPT pseudo-RR in a request should be taken as an
indication that the requestor fully implements the given version of
EDNS, and can correctly understand any response that conforms to that
feature's specification.
Lack of presence of an OPT record in a request MUST be taken as an
indication that the requestor does not implement any part of this
specification and that the responder MUST NOT use any protocol
extension described here in its response.
Responders who do not implement these protocol extensions MUST
respond with FORMERR messages without any OPT record.
If there is a problem with processing the OPT record itself, such as
an option value that is badly formatted or includes out of range
values, a FORMERR MAY be retured. If this occurs the response MUST
include an OPT record. This MAY be used to distinguish between
servers whcih do not implement EDNS and format errors within EDNS.
If EDNS is used in a request, and the response arrives with TC set
and with no EDNS OPT RR, a requestor SHOULD assume that truncation
prevented the OPT RR from being appended by the responder, and
further, that EDNS is not used in the response. Correspondingly, an
EDNS responder who cannot fit all necessary elements (including an
OPT RR) into a response, SHOULD respond with a normal (unextended)
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DNS response, possibly setting TC if the response will not fit in the
unextended response message's 512-octet size.
8. Security Considerations
Requestor-side specification of the maximum buffer size may open a
new DNS denial of service attack if responders can be made to send
messages which are too large for intermediate gateways to forward,
thus leading to potential ICMP storms between gateways and
responders.
Announcing very large UDP buffer sizes may result in dropping by
firewalls. This could cause retransmissions with no hope of success.
Some devices reject fragmented UDP packets.
Announcing too small UDP buffer sizes may result in fallback to TCP.
This is especially important with DNSSEC, where answers are much
larger.
9. IANA Considerations
The IANA has assigned RR type code 41 for OPT.
[RFC2671] specified a number of IANA sub-registries within "DOMAIN
NAME SYSTEM PARAMETERS:" "EDNS Extended Label Type", "EDNS Option
Codes", "EDNS Version Numbers", and "Domain System Response Code."
IANA is advised to re-parent these subregistries to this document.
RFC 2671 created an extended label type registry. We request that
this registry be closed.
This document assigns extended label type 0bxx111111 as "Reserved for
future extended label types." We request that IANA record this
assignment.
This document assigns option code 65535 to "Reserved for future
expansion."
This document expands the RCODE space from 4 bits to 12 bits. This
will allow IANA to assign more than the 16 distinct RCODE values
allowed in RFC 1035 [RFC1035].
This document assigns EDNS Extended RCODE "16" to "BADVERS".
IESG approval should be required to create new entries in the EDNS
Extended Label Type or EDNS Version Number registries, while any
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published RFC (including Informational, Experimental, or BCP) should
be grounds for allocation of an EDNS Option Code.
10. Acknowledgements
Paul Mockapetris, Mark Andrews, Robert Elz, Don Lewis, Bob Halley,
Donald Eastlake, Rob Austein, Matt Crawford, Randy Bush, and Thomas
Narten were each instrumental in creating and refining this
specification.
11. References
11.1. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)",
RFC 2671, August 1999.
[RFC3225] Conrad, D., "Indicating Resolver Support of DNSSEC",
RFC 3225, December 2001.
11.2. Informative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Authors' Addresses
Michael Graff
Internet Systems Consortium
950 Charter Street
Redwood City, California 94063
US
Phone: +1 650.423.1304
Email: mgraff@isc.org
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Paul Vixie
Internet Systems Consortium
950 Charter Street
Redwood City, California 94063
US
Phone: +1 650.423.1301
Email: vixie@isc.org
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Network Working Group M. Andrews
Internet-Draft ISC
Intended status: BCP November 19, 2009
Expires: May 23, 2010
Locally-served DNS Zones
draft-ietf-dnsop-default-local-zones-09
Abstract
Experience with the Domain Name System (DNS) has shown that there are
a number of DNS zones 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 Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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.
This Internet-Draft will expire on May 23, 2010.
Copyright Notice
Copyright (c) 2009 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
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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 BSD License.
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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Reserved Words . . . . . . . . . . . . . . . . . . . . . . 3
2. Effects on sites using RFC 1918 addresses. . . . . . . . . . . 4
3. Changes to Iterative Resolver Behaviour. . . . . . . . . . . . 4
4. Lists Of Zones Covered . . . . . . . . . . . . . . . . . . . . 5
4.1. RFC1918 Zones . . . . . . . . . . . . . . . . . . . . . . 5
4.2. RFC3330 Zones . . . . . . . . . . . . . . . . . . . . . . 6
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
Appendix A. Change History [To Be Removed on Publication] . . . . 10
A.1. draft-ietf-dnsop-default-local-zones-09.txt . . . . . . . 10
A.2. draft-ietf-dnsop-default-local-zones-08.txt . . . . . . . 10
A.3. draft-ietf-dnsop-default-local-zones-07.txt . . . . . . . 10
A.4. draft-ietf-dnsop-default-local-zones-06.txt . . . . . . . 10
A.5. draft-ietf-dnsop-default-local-zones-05.txt . . . . . . . 11
A.6. draft-ietf-dnsop-default-local-zones-04.txt . . . . . . . 11
A.7. draft-ietf-dnsop-default-local-zones-03.txt . . . . . . . 11
A.8. draft-ietf-dnsop-default-local-zones-02.txt . . . . . . . 11
A.9. draft-ietf-dnsop-default-local-zones-01.txt . . . . . . . 11
A.10. draft-ietf-dnsop-default-local-zones-00.txt . . . . . . . 11
A.11. draft-andrews-full-service-resolvers-03.txt . . . . . . . 11
A.12. draft-andrews-full-service-resolvers-02.txt . . . . . . . 12
Appendix B. Proposed Status [To Be Removed on Publication] . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
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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].
This recommendation is made because data has shown that significant
leakage of queries for these name spaces is occurring, despite
instructions to restrict them, and because it has therefore become
necessary to deploy sacrificial name servers to protect the immediate
parent name servers for these zones from excessive, unintentional,
query load [AS112] [I-D.draft-ietf-dnsop-as112-ops]
[I-D.draft-ietf-dnsop-as112-under-attack-help-help]. 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 name spaces but drop the
responses, put a significant load on the root servers (forward but no
reverse zones 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
which 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].
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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 which have local copies of the zone. Therefore this
recommendation will not be relevant.
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. This document recommends 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 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 name server.
Below is an example of a generic empty zone in master file format.
It will produce a negative cache TTL of 3 hours.
@ 10800 IN SOA @ nobody.invalid. 1 3600 1200 604800 10800
@ 10800 IN NS @
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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 name server is expected to abort UPDATE processing in the client.
4. Lists Of Zones Covered
The following subsections are intended to seed the IANA registry as
requested in the IANA Considerations Section. The zone name is the
entity to be registered.
4.1. RFC1918 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 |
+----------------------+
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4.2. RFC3330 Zones
The following zones correspond to those address ranges from [RFC3330]
that are not expected to appear as source or destination addresses on
the public Internet and to not have a unique name to associate with.
The recommendation to serve an empty zone 127.IN-ADDR.ARPA is not a
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 no other
coverage for these domains exists.
+------------------------------+------------------------+
| Zone | Description |
+------------------------------+------------------------+
| 0.IN-ADDR.ARPA | IPv4 "THIS" NETWORK |
| 127.IN-ADDR.ARPA | IPv4 LOOP-BACK NETWORK |
| 254.169.IN-ADDR.ARPA | IPv4 LINK LOCAL |
| 2.0.192.IN-ADDR.ARPA | IPv4 TEST NET |
| 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 a 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:
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+--------------+
| Zone |
+--------------+
| D.F.IP6.ARPA |
+--------------+
4.5. IPv6 Link Local Addresses
IPv6 Link-Local Addresses as of [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 a 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
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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 name servers are provided for these addresses.
This document also ignores IP6.INT. IP6.INT has been wound up with
only legacy resolvers now generating reverse queries under IP6.INT
[RFC4159].
This document has also deliberately ignored names immediately under
the root domain. While there is a subset of queries to the root name
servers which 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
This document requests that IANA establish a registry of zones which
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].
IANA should co-ordinate with the RIRs to ensure that, as 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 name server(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
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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., Thomson, A., 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 2398, March 1998.
[RFC2606] Eastlake, 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 IPv6", 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.
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[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,
October 2008.
9.2. Informative References
[AS112] "AS112 Project", <http://www.as112.net/>.
[I-D.draft-ietf-dnsop-as112-ops]
Abley, J. and W. Maton, "AS112 Nameserver Operations",
draft-ietf-dnsop-as112-ops-01 (work in progress),
November 2007.
[I-D.draft-ietf-dnsop-as112-under-attack-help-help]
Abley, J. and W. Maton, "I'm Being Attacked by
PRISONER.IANA.ORG!",
draft-ietf-dnsop-as112-under-attack-help-help-01 (work in
progress), November 2007.
[RFC3330] "Special-Use IPv4 Addresses", RFC 3330, September 2002.
[RFC3849] Huston, G., Lord, A., and P. Smith, "IPv6 Address Prefix
Reserved for Documentation", RFC 3849, July 2004.
Appendix A. Change History [To Be Removed on Publication]
A.1. draft-ietf-dnsop-default-local-zones-09.txt
refresh awaiting writeup
A.2. draft-ietf-dnsop-default-local-zones-08.txt
editorial, reference updates
A.3. draft-ietf-dnsop-default-local-zones-07.txt
none, expiry prevention
A.4. draft-ietf-dnsop-default-local-zones-06.txt
add IPv6 example prefix
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A.5. draft-ietf-dnsop-default-local-zones-05.txt
none, expiry prevention
A.6. draft-ietf-dnsop-default-local-zones-04.txt
Centrally Assigned Local addresses -> Non-Locally Assigned Local
address
A.7. draft-ietf-dnsop-default-local-zones-03.txt
expanded section 4 descriptions
Added references [RFC2136], [RFC3596],
[I-D.draft-ietf-dnsop-as112-ops] and
[I-D.draft-ietf-dnsop-as112-under-attack-help-help].
Revised language.
A.8. draft-ietf-dnsop-default-local-zones-02.txt
RNAME now "nobody.invalid."
Revised language.
A.9. draft-ietf-dnsop-default-local-zones-01.txt
Revised impact description.
Updated to reflect change in IP6.INT status.
A.10. draft-ietf-dnsop-default-local-zones-00.txt
Adopted by DNSOP.
"Author's Note" re-titled "Zones that are Out-Of-Scope"
Add note that these zone are expected to seed the IANA registry.
Title changed.
A.11. draft-andrews-full-service-resolvers-03.txt
Added "Proposed Status".
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A.12. draft-andrews-full-service-resolvers-02.txt
Added 0.IN-ADDR.ARPA.
Appendix B. Proposed Status [To Be Removed on Publication]
This Internet-Draft is being submitted for eventual publication as an
RFC with a proposed status of Best Current Practice.
Author's Address
Mark P. Andrews
Internet Systems Consortium
950 Charter Street
Redwood City, CA 94063
US
Email: Mark_Andrews@isc.org
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