Internet DRAFT - draft-hoffman-dns-terminology
draft-hoffman-dns-terminology
Network Working Group P. Hoffman
Internet-Draft VPN Consortium
Intended status: Best Current Practice A. Sullivan
Expires: September 7, 2015 Dyn
K. Fujiwara
JPRS
March 06, 2015
DNS Terminology
draft-hoffman-dns-terminology-02
Abstract
The DNS is defined in literally dozens of different RFCs. The
terminology used in by implementers and developers of DNS protocols,
and by operators of DNS systems, has sometimes changed in the decades
since the DNS was first defined. This document gives current
definitions for many of the terms used in the DNS in a single
document.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on September 7, 2015.
Copyright Notice
Copyright (c) 2015 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
Hoffman, et al. Expires September 7, 2015 [Page 1]
Internet-Draft DNS Terminology March 2015
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Names . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. DNS Message Format . . . . . . . . . . . . . . . . . . . . . 4
4. Response Codes . . . . . . . . . . . . . . . . . . . . . . . 5
5. Resource Records . . . . . . . . . . . . . . . . . . . . . . 6
6. DNS Servers . . . . . . . . . . . . . . . . . . . . . . . . . 6
7. Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8. Registration Model . . . . . . . . . . . . . . . . . . . . . 11
9. General DNSSEC . . . . . . . . . . . . . . . . . . . . . . . 12
10. DNSSEC States . . . . . . . . . . . . . . . . . . . . . . . . 13
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
12. Security Considerations . . . . . . . . . . . . . . . . . . . 15
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
14.1. Normative References . . . . . . . . . . . . . . . . . . 16
14.2. Informative References . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
The domain name system (DNS) is a simple query-response protocol
whose messages in both directions have the same format. The protocol
and message format are defined in [RFC1034] and [RFC1035]. These
RFCs defined some terms, but later documents defined others. Some of
the terms from RFCs 1034 and 1035 now have somewhat different
meanings than they did in 1987.
This document collects a wide variety of DNS-related terms. Some of
them have been precisely defined in earlier RFCs, some have been
loosely defined in earlier RFCs, and some are not defined in any
earlier RFC at all.
The definitions here are believed to be the consensus definition of
the DNS community, both protocol developers and operators. Some of
the definitions differ from earlier RFCs, and those differences are
noted. The terms are organized loosely by topic. Some definitions
are for new terms for things that are commonly talked about in the
DNS community but that never had terms defined for them.
In this document, where the consensus definition is the same as the
one in an RFC, that RFC is quoted. Where the consensus definition
Hoffman, et al. Expires September 7, 2015 [Page 2]
Internet-Draft DNS Terminology March 2015
has changed somewhat, the RFC is mentioned but the new stand-alone
definition is given.
Other organizations sometimes define DNS-related terms their own way.
For example, the W3C defines "domain" at
https://specs.webplatform.org/url/webspecs/develop/.
Note that there is no single consistent definition of "the DNS". It
can be considered to be some combination of the following: a
commonly-used naming scheme for objects on the Internet; a database
representing the names and certain properties of these objects; an
architecture providing distributed maintenance, resilience, and loose
coherency for this database; and a simple query-response protocol (as
mentioned in the current draft) implementing this architecture.
Capitalization in DNS terms is often inconsistent between RFCs and
between DNS practitioners. The capitalization used in this document
is a best guess at current practices, and is not meant to indicate
that other capitalization styles are wrong or archaic.
2. Names
Domain name -- Section 3.1 of RFC 1034 talks of "the domain name
space" as a tree structure. "Each node has a label, which is zero to
63 octets in length. ... The domain name of a node is the list of the
labels on the path from the node to the root of the tree. ... To
simplify implementations, the total number of octets that represent a
domain name (i.e., the sum of all label octets and label lengths) is
limited to 255."
Fully-qualified domain name (FQDN) -- This is often just a clear way
of saying the same thing as "domain name of a node", as outlined
above. However, the term is ambiguous. Strictly speaking, a fully-
qualified name would include every label, including the final, zero-
length label of the root zone: such a name would be written
"www.example.net." (note the terminating dot). But because every
name eventually shares the common root, names are often written
relative to the root (such as "www.example.net") and are still called
"fully qualified".
This term first appeared in [RFC1206].
Host name -- This term and its equivalent, "hostname", have been
widely used but are not defined in RFC 1034, 1035, 1123, or 2181.
The DNS was originally deployed into the Host Tables environment as
outlined in [RFC0952], and it is likely that the term followed
informally from the definition there. Over time, the definition
seems to have shifted. "Host name" is often meant to be a domain
name that follows the rules in Section 3.5 of RFC 1034, the
Hoffman, et al. Expires September 7, 2015 [Page 3]
Internet-Draft DNS Terminology March 2015
"preferred name syntax". Note that any label in any domain name can
contain any octet value; hostnames are generally considered to be
domain names where every label follows the rules in the "preferred
name syntax", with the amendment that labels can start with ASCII
digits (this amendment comes from Section 2.1 of [RFC1123]).
People also sometimes use the term hostname to refer to just the
first label of an FQDN. In addition, people sometimes use this term
to describe any name that refers to a machine, and those might
include labels that do not conform to the "preferred name syntax".
TLD -- A Top-Level Domain, meaning a zone that is one layer below the
root, such as .com or .jp. There is nothing special, from the point
of view of the DNS, about TLDs. Most of them are also delegation-
centric zones, and there are significant policy issues around their
operation.
ccTLD -- A TLD that is allocated to a country. Historically, these
were two-letter TLDs, and were allocated to countries using the two-
letter code from the ISO 3166-1 alpha-2 standard [ISO3166]. In
recent years, there have been allocations of TLDs that conform to
IDNA2008 ([RFC5890], [RFC5891], [RFC5892], [RFC5893], and [RFC5894]);
these are still treated as ccTLDs for policy purposes.
gTLD -- A "generic" TLD is a TLD that is not a ccTLD, and is not one
of the small number of historical TLDs such as .int and .arpa. There
is no precise definition for which TLDs that are not ccTLDs are
gTLDs.
3. DNS Message Format
Header -- The first 12 octets of a DNS message. Many of the fields
and flags in the header diagram in section 4.1.1 of RFC 1035 are
referred to by their names in that diagram. For example, the
response codes are called "RCODEs", and the authoritative answer bit
is often called "the AA flag" or "the AA bit". RCODEs are covered in
Section 4.
TTL -- The maximum "time to live" of a resource record. A TTL value
is an unsigned number, with a minimum value of 0, and a maximum value
of 2147483647. That is, a maximum of 2^31 - 1. When transmitted,
the TTL is encoded in the less significant 31 bits of the 32 bit TTL
field, with the most significant, or sign, bit set to zero. (Quoted
from [RFC2181], section 8) (Note that RFC 1035 erroneously stated
that this is a signed integer; it is fixed in an erratum.)
The TTL "specifies the time interval that the resource record may be
cached before the source of the information should again be
Hoffman, et al. Expires September 7, 2015 [Page 4]
Internet-Draft DNS Terminology March 2015
consulted". (Quoted from RFC 1035, section 3.2.1) Also: "the time
interval (in seconds) that the resource record may be cached before
it should be discarded". (Quoted from RFC 1035, section 4.1.3).
Despite being defined for a resource record, the TTL of every
resource record in an RRset is required to be the same (RFC2181,
section 5.2).
The reason that the TTL is the maximum time to live is that a cache
operator might decide to shorten the time to live for operational
purposes, such as if there is a policy to not allow TTL values over a
certain number. Also, if a value is flushed from the cache when its
value is still positive, the value effectively becomes zero.
There is also the concept of a "default TTL" for a zone, which can be
a configuration parameter in the server software. This is often
expressed by a default for the entire server, and an default override
for a zone using the $TTL directive in a zone file. The $TTL
directive was added to the master file format by [RFC2308].
Glue records -- Resource records which are not part of the
authoritative data, and are address resource records for the servers
listed in the message. They contain data that allows access to name
servers for subzones. (Definition from RFC 1034, section 4.2.1)
Referrals -- Data from the authority section of a non-authoritative
answer. RFC 1035 section 2.1 defines "authoritative" data. However,
referrals at zone cuts are not authoritative. Referrals may be a
zone cut NS resource records and their glue. NS records on the
parent side of a zone cut are an authoritative delegation, but are
not treated as authoritative data by the client. [[ A more complete
and precise definition will be needed here. ]]
4. Response Codes
Some of response codes that are defined in RFC 1035 have gotten their
own shorthand names. Some common response code (RCODE) names that
appear without reference to the numeric value are "FORMERR",
"SERVFAIL", and "NXDOMAIN". All of the RCODEs are listed at
http://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml,
although that site uses mixed-case capitalization, while most
documents use all-caps.
NODATA -- This is not an actual response code, but instead is the
combination of an RCODE of 0 (NOERROR) and an Answer section that is
empty. That is, it indicates that the response is no answer, but
that there was not supposed to be one. Section 1 of RFC 2308 defines
it as "a pseudo RCODE which indicates that the name is valid, for the
given class, but are no records of the given type."
Hoffman, et al. Expires September 7, 2015 [Page 5]
Internet-Draft DNS Terminology March 2015
5. Resource Records
RR -- A short form for resource record. (RFC 1034, section 3.6.)
RRset -- A set of resource records with the same label, class and
type, but with different data. (Definition from RFC 2181) Also
spelled RRSet in some documents. As a clarification, "same label" in
this definition means "same owner name".
OPT -- A pseudo-RR (sometimes called a meta-RR) that is used only to
contain control information pertaining to the question-and-answer
sequence of a specific transaction. (Definition from [RFC6891],
section 6.1.1)
Owner -- The domain name where a RR is found (RFC 1034, section 3.6).
Often appears in the term "owner name".
SOA field names -- DNS documents, including the definitions here,
often refer to the fields in the RDATA an SOA resource record by
field name. Those fields are defined in Section 3.3.13 of RFC 1035.
The names (in the order they appear in the SOA RDATA) are MNAME,
RNAME, SERIAL, REFRESH, RETRY, and EXPIRE, MINIMUM. Note that the
meaning of MINIMUM field is updated in Section 4 of RFC 2308; the new
definition is that the MINIMUM field is only "the TTL to be used for
negative responses".
6. DNS Servers
This section defines the terms used for the systems that act as DNS
clients, DNS servers, or both. Some terms about servers describe
servers that do and do not use DNSSEC; see Section 9 for those
definitions.
[[ There is a request to "first describe the iterative and recursive
resolution processes, and mention the expected values of the RD,RA,AA
bits. Then you can describe the distinctions between recursive and
iterative clients, and between recursive and authoritative servers,
in terms of the roles they play in the different resolution
processes." This would require the section to be quite different
than the other sections in the document. ]]
Resolver -- A program that extracts information from name servers in
response to client requests. (Quoted from RFC 1034, section 2.4) It
is a program that interfaces user programs to domain name servers.
The resolver is located on the same machine as the program that
requests the resolver's services. (Quoted from RFC 1034, section
5.1) A resolver performs queries for a name, type, and class, and
receives answers. The logical function is called "resolution". In
Hoffman, et al. Expires September 7, 2015 [Page 6]
Internet-Draft DNS Terminology March 2015
practice, the term is usually referring to some specific type of
resolver (some of which are defined below), and understanding the use
of the term depends on understanding the context.
Stub resolver -- A resolver that cannot perform all resolution
itself. Stub resolvers generally depend on a recursive resolver to
undertake the actual resolution function. Stub resolvers are
discussed but never fully defined in RFC 1034, section 5.3.1.
Iterative mode -- A resolution mode of a server that receives DNS
queries and responds with a referral to another server. Section 2.3
of RFC 1034 describes this as "The server refers the client to
another server and lets the client pursue the query". A resolver
that works in iterative mode is sometimes called an "iterative
resolver".
Recursive mode -- A resolution mode of a server that receives DNS
queries and either responds to those queries from a local cache or
sends queries to other servers in order to get the final answers to
the original queries. Section 2.3 of RFC 1034 describes this as "The
first server pursues the query for the client at another server". A
server operating in recursive mode may be thought of as having a name
server side (which is what answers the query) and a resolver side
(which performs the resolution function). Systems operating in this
mode are commonly called "recursive servers". Sometimes they are
called "recursive resolvers". While strictly the difference between
these is that one of them sends queries to another recursive server
and the other does not, in practice it is not possible to know in
advance whether the server that one is querying will also perform
recursion; both terms can be observed in use interchangeably.
Priming -- The mechanism used by a resolvrer to determine where to
send queries before there is anything in the resolver's cache.
Priming is most often done from a configuration setting that contains
a list of authoritative servers for the DNS root zone.
Negative caching -- The storage of knowledge that something does not
exist, cannot give an answer, or does not give an answer. (Quoted
from Section 1 of RFC 2308)
Authoritative server -- A system that responds to DNS queries with
information about zones for which it has been configured to answer
with the AA flag in the response header set to 1. It is a server
that has authority over one or more DNS zones. Note that it is
possible for an authoritative server to respond to a query without
the parent zone delegating authority to that server.
Hoffman, et al. Expires September 7, 2015 [Page 7]
Internet-Draft DNS Terminology March 2015
Slave -- An authoritative server which uses zone transfer to retrieve
the zone. (Quoted from [RFC1996], section 2.1)
Master -- Any authoritative server configured to be the source of
zone transfer for one or more slave servers. (Quoted from RFC 1996,
section 2.1)
Primary master -- The primary master is named in the zone's SOA MNAME
field and optionally by an NS resource record. (Quoted from RFC
1996, section 2.1)
Stealth server -- This is the same as a slave server except that it
is not listed in an NS resource record for the zone. (Quoted from
RFC 1996, section 2.1) A stealth server is often actually a master
for zone transfers, and in that case is called a "hidden master".
Zone transfer -- The act of a client requesting a copy of a zone and
an authoritative server sending the needed information. There are
two common standard ways to do zone transfers: the AXFR
("Authoritative Transfer") mechanism to copy the full zone, and the
IXFR ("Incremental Transfer") mechanism to copy only parts of the
zone that have changed. Many systems use non-standard methods for
zone transfer outside the DNS protocol.
DNS forwarder -- A system that receives a DNS query, possibly changes
the query, sends the resulting query to a recursive resolver,
receives the response from a resolver, possibly changes the response,
and sends the resulting response to the stub resolver. Section 1 of
RFC 2308 describes a forwarder as "a nameserver used to resolve
queries instead of directly using the authoritative nameserver
chain". RFC further says "The forwarder typically either has better
access to the internet, or maintains a bigger cache which may be
shared amongst many resolvers."
[RFC5625] does not give a specific definition for DNS forwarder, but
describes in detail what features they need to support. The protocol
interfaces for DNS forwarders are exactly the same as those for
recursive resolvers (for interactions with DNS stubs) and as those
for stub resolvers (for interactions with recursive resolvers).
Full resolver -- This term is used in RFC 1035, but it is not defined
there. RFC 1123 defines a "full-service resolver" that may or may
not be what was intended by "full resolver" in RFC 1035. In the
vernacular, a full-service resolver is usually one that would be
suitable for use by a stub resolver.
Consensual policy-implementing resolver -- A resolver that changes
some answers it returns based on policy criteria, such as to prevent
Hoffman, et al. Expires September 7, 2015 [Page 8]
Internet-Draft DNS Terminology March 2015
access to malware sites. These policy criteria are agreed to by
systems that query this resolver through some out of band mechanism
(such as finding out about the resolver from a web site and reading
the policy).
Non-consensual policy-implementing resolver -- A resolver that is not
a consensual policy-implementing resolver that changes the answers it
returns. The difference between this and a consensual policy-
implementing resolver is that users of this resolver are not expected
to know that there is a policy to change the answers it returns.
Open resolver -- A full resolver that accepts and processes queries
from any (or nearly any) stub resolver. This is sometimes also
called a "public resolver".
Open forwarder -- A DNS forwarder that accepts and forwards queries
from any (or nearly any) stub resolver to a full resolver.
Views -- A view is a configuration for a server that allows it to
provide different answers depending on the address on the query.
Views are often used to provide more names or different addresses to
queries from "inside" a protected network than to those "outside"
that network. Views are not a standardized part of the DNS, but they
are widely implemented in server software.
Passive DNS -- A mechanism to collect large amounts of DNS data by
storing queries and responses from many recursive resolvers. Passive
DNS databases can be used to answer historical questions about DNS
zones such as which records were available for them at what times in
the past.
Child-centric resolver -- A DNS resolver that, instead of serving the
NS RRset and glue records that it obtained from the parent of a zone,
serves data from the authoritative servers for that zone. The term
"child-centric" is meant as the opposite of "parent-centric", which
means a resolver that simply serves the NS RRset and glue records for
a zone that it obtained from the zone's parent, without checking the
authoritative servers for that zone.
7. Zones
This section defines terms that are used when discussing zones that
are being served or retrieved.
Zone -- A unit of organization of authoritative data. Zones can be
automatically distributed to the name servers which provide redundant
service for the data in a zone. (Quoted from RFC 1034, section 2.4).
Hoffman, et al. Expires September 7, 2015 [Page 9]
Internet-Draft DNS Terminology March 2015
Child -- The entity on record that has the delegation of the domain
from the Parent. (Quoted from [RFC7344], section 1.1)
Parent -- The domain in which the Child is registered. (Quoted from
RFC 7344, section 1.1) Earlier, "parent name server" was defined in
[RFC0882] as "the name server that has authority over the place in
the domain name space that will hold the new domain".
Origin -- 1. The domain name that appears at the top of a zone. 2.
The domain name within which a given relative domain name appears in
zone files. Generally seen in the context of "$ORIGIN", which is a
control entry defined in RFC 1035, section 5.1, as part of the master
file format. For example, if the $ORIGIN is set to "example.org.",
then a master file line for "www" is in fact an entry for
"www.example.org.".
Zone cut -- The delimitation point between two zones where the origin
of one of the zones is the child of the other zone. (Section 6 of
RFC 2181 uses this term extensively, although never actually defines
it.) Section 4.2 of RFC 1034 uses "cuts" as "zone cut".
Apex -- The point in the tree at an owner of an SOA and corresponding
authoritative NS RRset. This is also called the "zone apex". The
"apex" is a data-theoretic description of a tree structure, and
"origin" is the name of the same concept when it is implemented in
zone files.
Delegation -- The process by which a separate zone is created in the
name space beneath the apex of a given domain. Delegation happens
when an NS RRset is added in the parent zone for the child origin,
and a corresponding zone apex is created at the child origin.
Delegation inherently happens at a zone cut.
In-bailiwick response -- A response in which the name server
answering is authoritative for an ancestor of the owner name in the
response. The term normally is used when discussing the relevancy of
glue records. For example, the parent zone example.com might reply
with glue records for ns.child.example.com. Because the
child.example.com zone is a descendant of the example.com zone, the
glue is in-bailiwick.
Out-of-bailiwick response -- A response in which the name server
answering is not authoritative for an ancestor of the owner name in
the response.
Authoritative data -- All of the RRs attached to all of the nodes
from the top node of the zone down to leaf nodes or nodes above cuts
around the bottom edge of the zone. (Quoted from Section 4.2.1 of
Hoffman, et al. Expires September 7, 2015 [Page 10]
Internet-Draft DNS Terminology March 2015
RFC 1034) It is noted that this definition might inadvertently also
include any NS records that appear in the zone, even those that might
not truly be authoritative because there are identical NS RRs below
the zone cut. This reveals the ambiguity in the notion of
authoritative data, because the parent-size NS records
authoritatively indicate the delegation, even though they are not
themselves authoritative data.
Root zone -- The zone whose origin is the zero-length label. Also
sometimes called "the DNS root".
Empty non-terminal -- A domain name that has no RRsets, but has
descendants that have RRsets. A typical example is in SRV records:
in the name "_sip._tcp.example.com", it is likely that
"_tcp.example.com" has no RRsets, but that "_sip._tcp.example.com"
has (at least) an SRV RRset.
Delegation-centric zone -- A zone which consists mostly of
delegations to child zones. This term is used in contrast to a zone
which might have some delegations to child zones, but also has many
data resource records for the zone itself and/or for child zones.
Wildcard -- RFC 1034 defined "wildcard", but in a way that turned out
to be confusing to implementers. For an extended discussion of
wildcards, including clearer definitions, see [RFC4592].
Occluded name -- The addition of a delegation point via dynamic
update will render all subordinate domain names to be in a limbo,
still part of the zone but not available to the lookup process. The
addition of a DNAME resource record has the same impact. The
subordinate names are said to be "occluded". (Quoted from [RFC5936],
Section 3.5)
8. Registration Model
Registry -- The administrative operation of a zone that allows
registration of names within that zone.
Registrant -- An individual or organization on whose behalf a name in
a zone is registered by the registry. In many zones, the registry
and the registrant may be the same entity, but in TLDs they often are
not.
Registrar -- A service provider that acts as a go-between for
registrants and registries. Not all registrations require a
registrar, though it is common to have registrars be involved in
registrations in TLDs.
Hoffman, et al. Expires September 7, 2015 [Page 11]
Internet-Draft DNS Terminology March 2015
EPP -- The Extensible Provisioning Protocol (EPP), which is commonly
used for communication of registration information between registries
and registrars. EPP is defined in [RFC5730].
9. General DNSSEC
Most DNSSEC terms are defined in [RFC4033], [RFC4034], and [RFC4035].
The terms that have caused confusion in the DNS community are
highlighted here.
DNSSEC-aware and DNSSEC-unaware -- Section 2 of RFC 4033 defines many
types of resolvers and validators. In specific, the terms "non-
validating security-aware stub resolver", "non-validating stub
resolver", "security-aware name server", "security-aware recursive
name server", "security-aware resolver", "security-aware stub
resolver", and "security-oblivious 'anything'" are all defined.
Signed zone -- A zone whose RRsets are signed and that contains
properly constructed DNSKEY, Resource Record Signature (RRSIG), Next
Secure (NSEC), and (optionally) DS records. (Quoted from RFC 4033,
section 2) It has been noted in other contexts that the zone itself
is not really signed, but all the relevant RRsets in the zone are
signed. It should also be noted that, since the publication of
[RFC6840], NSEC records are no longer required for signed zones: a
signed zone might include NSEC3 records instead.
Unsigned zone -- Section 2 of RFC 4033 defines this as "a zone that
is not signed". Section 2 of RFC 4035 defines this as "A zone that
does not include these records [properly constructed DNSKEY, Resource
Record Signature (RRSIG), Next Secure (NSEC), and (optionally) DS
records] according to the rules in this section". There is an
important note at the end of Section 5.2 of RFC 4035 adding an
additional situation when a zone is considered unsigned: "If the
resolver does not support any of the algorithms listed in an
authenticated DS RRset, then the resolver will not be able to verify
the authentication path to the child zone. In this case, the
resolver SHOULD treat the child zone as if it were unsigned."
NSEC -- The NSEC resource record lists two separate things: the next
owner name (in the canonical ordering of the zone) that contains
authoritative data or a delegation point NS RRset, and the set of RR
types present at the NSEC RR's owner name. (Quoted from Section 4 of
4034)
NSEC3 -- The NSEC3 resource record is quite different than the NSEC
resource record. NSEC3 resource records are defined in [RFC5155].
Hoffman, et al. Expires September 7, 2015 [Page 12]
Internet-Draft DNS Terminology March 2015
Opt-out -- The Opt-Out Flag indicates whether this NSEC3 RR may cover
unsigned delegations. (Quoted from Section 3.1.2.1 of RFC 5155)
DNSSEC Policy (DP) -- A statement that sets forth the security
requirements and standards to be implemented for a DNSSEC-signed
zone. (Quoted from [RFC6841], section 2)
DNSSEC Practice Statement (DPS) -- A practices disclosure document
that may support and be a supplemental document to the DNSSEC Policy
(if such exists), and it states how the management of a given zone
implements procedures and controls at a high level. (Quoted from RFC
6841, section 2)
Key signing key (KSK) -- DNSSEC keys that only sign the apex DNSKEY
RRset in a zone. (Quoted from [RFC6781], Section 3.1)
Zone signing key (ZSK) -- DNSSEC keys that can be used to sign all
the RRsets in a zone that require signatures, other than the apex
DNSKEY RRset. (Quoted from RFC 6781, Section 3.1)
10. DNSSEC States
A validating resolver can determine that a response is in one of four
states: secure, insecure, bogus, or indeterminate. These states are
defined in RFC 4033 and 4035, although the two definitions differ a
bit.
Section 5 of RFC 4033 says:
Hoffman, et al. Expires September 7, 2015 [Page 13]
Internet-Draft DNS Terminology March 2015
A validating resolver can determine the following 4 states:
Secure: The validating resolver has a trust anchor, has a chain of
trust, and is able to verify all the signatures in the response.
Insecure: The validating resolver has a trust anchor, a chain of
trust, and, at some delegation point, signed proof of the
non-existence of a DS record. This indicates that subsequent
branches in the tree are provably insecure. A validating resolver
may have a local policy to mark parts of the domain space as
insecure.
Bogus: The validating resolver has a trust anchor and a secure
delegation indicating that subsidiary data is signed, but the
response fails to validate for some reason: missing signatures,
expired signatures, signatures with unsupported algorithms, data
missing that the relevant NSEC RR says should be present, and so
forth.
Indeterminate: There is no trust anchor that would indicate that a
specific portion of the tree is secure. This is the default
operation mode.
Section 4.3 of RFC 4035 says:
Hoffman, et al. Expires September 7, 2015 [Page 14]
Internet-Draft DNS Terminology March 2015
A security-aware resolver must be able to distinguish between four
cases:
Secure: An RRset for which the resolver is able to build a chain of
signed DNSKEY and DS RRs from a trusted security anchor to the
RRset. In this case, the RRset should be signed and is subject to
signature validation, as described above.
Insecure: An RRset for which the resolver knows that it has no chain
of signed DNSKEY and DS RRs from any trusted starting point to the
RRset. This can occur when the target RRset lies in an unsigned
zone or in a descendent of an unsigned zone. In this case, the
RRset may or may not be signed, but the resolver will not be able
to verify the signature.
Bogus: An RRset for which the resolver believes that it ought to be
able to establish a chain of trust but for which it is unable to
do so, either due to signatures that for some reason fail to
validate or due to missing data that the relevant DNSSEC RRs
indicate should be present. This case may indicate an attack but
may also indicate a configuration error or some form of data
corruption.
Indeterminate: An RRset for which the resolver is not able to
determine whether the RRset should be signed, as the resolver is
not able to obtain the necessary DNSSEC RRs. This can occur when
the security-aware resolver is not able to contact security-aware
name servers for the relevant zones.
11. IANA Considerations
This document has no effect on IANA registries.
12. Security Considerations
These definitions do not change any security considerations for the
DNS.
13. Acknowledgements
The authors gratefully acknowledge all of the authors of DNS-related
RFCs that proceed this one. Comments from Tony Finch, Stephane
Bortzmeyer, Niall O'Reilly, Colm MacCarthaigh, Ray Bellis, John
Kristoff, and others have helped shape this document. [[ More acks
will go here as people point out new terms to add and changes to the
ones we have listed here. ]]
Hoffman, et al. Expires September 7, 2015 [Page 15]
Internet-Draft DNS Terminology March 2015
14. References
14.1. Normative References
[ISO3166] International Organization for Standardization (ISO),
"Country Codes - ISO 3166", February 2015,
<http://www.iso.org/iso/country_codes/country_codes>.
[RFC0882] Mockapetris, P., "Domain names: Concepts and facilities",
RFC 882, November 1983.
[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.
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application
and Support", STD 3, RFC 1123, October 1989.
[RFC1206] Malkin, G. and A. Marine, "FYI on Questions and Answers:
Answers to commonly asked "new Internet user" questions",
RFC 1206, February 1991.
[RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone
Changes (DNS NOTIFY)", RFC 1996, August 1996.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, July 1997.
[RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS
NCACHE)", RFC 2308, March 1998.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", RFC
4033, March 2005.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, March 2005.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, March 2005.
[RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name
System", RFC 4592, July 2006.
Hoffman, et al. Expires September 7, 2015 [Page 16]
Internet-Draft DNS Terminology March 2015
[RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
Security (DNSSEC) Hashed Authenticated Denial of
Existence", RFC 5155, March 2008.
[RFC5730] Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
STD 69, RFC 5730, August 2009.
[RFC5936] Lewis, E. and A. Hoenes, "DNS Zone Transfer Protocol
(AXFR)", RFC 5936, June 2010.
[RFC6781] Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC
Operational Practices, Version 2", RFC 6781, December
2012.
[RFC6840] Weiler, S. and D. Blacka, "Clarifications and
Implementation Notes for DNS Security (DNSSEC)", RFC 6840,
February 2013.
[RFC6841] Ljunggren, F., Eklund Lowinder, AM., and T. Okubo, "A
Framework for DNSSEC Policies and DNSSEC Practice
Statements", RFC 6841, January 2013.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891, April 2013.
[RFC7344] Kumari, W., Gudmundsson, O., and G. Barwood, "Automating
DNSSEC Delegation Trust Maintenance", RFC 7344, September
2014.
14.2. Informative References
[RFC0952] Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet
host table specification", RFC 952, October 1985.
[RFC5625] Bellis, R., "DNS Proxy Implementation Guidelines", BCP
152, RFC 5625, August 2009.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010.
[RFC5891] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891, August 2010.
[RFC5892] Faltstrom, P., "The Unicode Code Points and
Internationalized Domain Names for Applications (IDNA)",
RFC 5892, August 2010.
Hoffman, et al. Expires September 7, 2015 [Page 17]
Internet-Draft DNS Terminology March 2015
[RFC5893] Alvestrand, H. and C. Karp, "Right-to-Left Scripts for
Internationalized Domain Names for Applications (IDNA)",
RFC 5893, August 2010.
[RFC5894] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Background, Explanation, and
Rationale", RFC 5894, August 2010.
Authors' Addresses
Paul Hoffman
VPN Consortium
127 Segre Place
Santa Cruz, CA 95060
USA
Email: paul.hoffman@vpnc.org
Andrew Sullivan
Dyn
150 Dow St, Tower 2
Manchester, NH 1604
USA
Email: asullivan@dyn.com
Kazunori Fujiwara
Japan Registry Services Co., Ltd.
Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda
Chiyoda-ku, Tokyo 101-0065
Japan
Phone: +81 3 5215 8451
Email: fujiwara@jprs.co.jp
Hoffman, et al. Expires September 7, 2015 [Page 18]
