Internet DRAFT - draft-muks-dnsop-dns-squash
draft-muks-dnsop-dns-squash
Internet Engineering Task Force M. Sivaraman
Internet-Draft Internet Systems Consortium
Intended status: Experimental April 1, 2018
Expires: October 3, 2018
DNS squash
draft-muks-dnsop-dns-squash-01
Abstract
This document attempts to specify current DNS protocol in squashed
form in a single document.
Status of This Memo
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This Internet-Draft will expire on October 3, 2018.
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Table of Contents
1. About this document . . . . . . . . . . . . . . . . . . . . . 2
2. Introduction to DNS . . . . . . . . . . . . . . . . . . . . . 3
3. Data structure . . . . . . . . . . . . . . . . . . . . . . . 3
4. Service operation . . . . . . . . . . . . . . . . . . . . . . 5
5. Wire protocol . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. DNS messages . . . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. Normative references . . . . . . . . . . . . . . . . . . . . 5
Appendix A. ChangeLog . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. About this document
Current DNS protocol is spread over several RFCs and drafts dating
back to 1987 (beginning from [RFC1033], [RFC1034], [RFC1035]). There
is no structure and order to be found in the publication of these
RFCs. The early DNS RFCs are insufficiently specified and some parts
of intermediate RFCs are obsolete. The internet has changed
significantly since 1987 and there are several security
considerations when implementing public-facing DNS. Learning the DNS
protocol pedantically for the purpose of implementing it is very very
difficult, and navigating the RFCs without any consistent ordering or
rationale is at best confusing to a newcomer.
This document attempts to provide a single structured reference of
the current "core" DNS protocol, squashing together the contents and
errata of the various DNS RFCs and drafts. It also attempts to
clarify DNS protocol where ambiguity exists.
It is expected that implementors and anybody who is interested in
protocol behavior will consult this document.
Following the robustness principle ("Be conservative in what you do,
be liberal in what you accept from others"), an implementation that
follows the behavior in this document is expected to be compatible
when talking with current implementations of DNS.
As everything is described here, this document need not contain any
normative references to older DNS RFCs and drafts, but for the sake
of citation, the source of requirements (where applicable) is
provided.
This document does not attempt to describe aspects such as the
history of DNS, operating system functions and API for DNS
operations, DNS utilities, etc. It is meant to be a pedantic network
protocol description only.
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Introduction to DNS
TBD.
3. Data structure
The domain name space is a tree data structure that maps DNS names to
some resource data about that name. Each node and leaf in the tree
corresponds to a key-value pair, where the key is a DNS name and the
value is resource data (which may be empty). The tree is used to
lookup resource data corresponding to a DNS name. The DNS makes no
distinctions between the uses of the interior nodes and leaves, and
this document uses the term "node" to refer to both.
Each node stores a label, which MUST be 1 to 63 octets in length for
all nodes except the root node for which the label MUST be empty.
Sibling nodes (sharing the same parent) MUST NOT have the same label,
although the same label can be used for nodes which are not siblings.
The DNS name of a node is the sequence of the labels on the path from
the node to the root of the tree.
A DNS name is printed as a concatenation left to right of the
individual labels on the path from the node to the root, each label
trailing with an ASCII period '.' character. Thus a complete printed
DNS name ends with a period character. See (TBD: link to proper DNS
name presentation formatting).
In wire format, a DNS name is represented as a concatenation left to
right of the individual labels on the path from the node to the root,
where each label is represented starting with the label length as a
single unsigned integer octet with values 0-63, and followed by the
octets of the label itself. For example, the following octets
represent a DNS name "example.org." ("example" labelled node followed
by "org" labelled node followed by root node):
{ 0x07, 'e', 'x', 'a', 'm', 'p', 'l', 'e', 0x03, 'o', 'r', 'g', 0x00 }
The total number of octets that represent a DNS name in wire format
(i.e., the sum of all label lengths and label octets) MUST NOT be
larger than 255. This requirement, and the other requirement that a
label be between 0 to 63 octets, limit the DNS names that may be
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represented in the domain name space. For example, a DNS name
"example.org." is 13 octets long in wire format.
The following figure shows a part of the current domain name space.
Note that the tree is a very small subset of the actual name space.
<empty-label>
|
|
+-----------------+------------------+
| | |
arpa com org
| | |
| | |
+-----------+ | +---------+--------+
| | | | | |
in-addr ip6 | example wikipedia isc
|
+--------+------------------+---------------+--------+
| | | | |
reddit apple | amazon xkcd
google
|
+-----+-----+--------+
| | | |
maps www mail translate
TBD: describe items in the tree
The octets that make up a label may contain any 8-bit value. In DNS
name comparisons, when the highest-order bit of an octet of a label
is 0, the value of that octet for comparison purposes is assumed to
be a 7-bit ASCII character and MUST be compared without character
case-sensitivity (i.e., the corresponding operand of the octet
comparison operator must be transformed to ASCII lowercase first and
then compared). When the highest-order bit of an octet of a label is
1, it MUST be compared directly without any character case
transformations.
This means that tree operations are not case-sensitive, and a tree
may contain a node with label "example", or a node with label
"EXAMPLE", but not both as siblings (sharing the same parent). The
node could be referred to either as "example", "EXAMPLE" or "ExAmPlE"
as they all corespond to the same node.
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A node in the domain name space MUST preserve the character case of
the octets of a label as they are entered into the tree, even though
tree operations are not case-sensitive.
A domain in the DNS is identified by a DNS name, and consists of that
part of the domain name space that is at or below the DNS name which
identifies it.
A DNS name is a sub-domain of another DNS name if it is contained
within the latter. This relationship can be tested by seeing if the
sub-domain's DNS name ends with the containing DNS name. For
example, "sub.example.org." is a sub-domain of "example.org.".
4. Service operation
TBD.
5. Wire protocol
5.1. DNS messages
TBD.
6. Acknowledgements
TBD.
7. Normative references
[RFC1033] Lottor, M., "Domain Administrators Operations Guide",
RFC 1033, DOI 10.17487/RFC1033, November 1987,
<https://www.rfc-editor.org/info/rfc1033>.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
Appendix A. ChangeLog
o draft-muks-dnsop-dns-squash-01
Add domain name space diagram and correct some mistakes.
o draft-muks-dnsop-dns-squash-00
Initial draft.
Author's Address
Mukund Sivaraman
Internet Systems Consortium
950 Charter Street
Redwood City, CA 94063
US
Email: muks@mukund.org
URI: https://www.isc.org/
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