draft-ietf-dnsext-axfr-clarify-09.txt   draft-ietf-dnsext-axfr-clarify-10.txt 
INTERNET-DRAFT Edward Lewis DNS Extensions Working Group Edward Lewis
draft-ietf-dnsext-axfr-clarify-09.txt NeuStar, Inc. INTERNET-DRAFT NeuStar, Inc.
Expires: July 1, 2009 January 2009
Updates: 1034, 1035 (if approved) Intended status: Standards Track Updates: 1034, 1035 (if approved)
Intended status: Standards Track
DNS Zone Transfer Protocol (AXFR) DNS Zone Transfer Protocol (AXFR)
draft-ietf-dnsext-axfr-clarify-10.txt
Status of this Memo Status of this Memo
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Abstract Abstract
The Domain Name System standard mechanisms for maintaining coherent The Domain Name System standard mechanisms for maintaining coherent
servers for a zone consist of three elements. One mechanism is the servers for a zone consist of three elements. One mechanism is the
Authoritative Transfer (AXFR) is defined in RFC 1034 and RFC 1035. Authoritative Transfer (AXFR) is defined in RFC 1034 and RFC 1035.
The definition of AXFR, has proven insufficient in detail, forcing The definition of AXFR, has proven insufficient in detail, forcing
implementations intended to be compliant to make assumptions, impeding implementations intended to be compliant to make assumptions, impeding
interoperability. Yet today we have a satisfactory set of interoperability. Yet today we have a satisfactory set of
implementations that do interoperate. This document is a new implementations that do interoperate. This document is a new
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currently. currently.
1.4 Coverage and Relationship to Original AXFR Specification 1.4 Coverage and Relationship to Original AXFR Specification
This document concentrates on just the definition of AXFR. Any effort This document concentrates on just the definition of AXFR. Any effort
to update the IXFR or NOTIFY mechanisms would be done in different to update the IXFR or NOTIFY mechanisms would be done in different
documents. documents.
The original "specification" of the AXFR sub-protocol is scattered The original "specification" of the AXFR sub-protocol is scattered
depicts the scenario for which AXFR has been designed. Section 4.3.5 depicts the scenario for which AXFR has been designed. Section 4.3.5
of RFC 1034 describes the zone synchronisation strategies in general of RFC 1034 describes the zone synchronization strategies in general
and rules for the invocation of a full zone transfer via AXFR; the and rules for the invocation of a full zone transfer via AXFR; the
fifth paragraph of that section contains a very short sketch of the fifth paragraph of that section contains a very short sketch of the
AXFR protocol. Section 3.2.3 of RFC 1035 has assigned the code point AXFR protocol. Section 3.2.3 of RFC 1035 has assigned the code point
for the AXFR QTYPE (see section 2.1.2 below for more details). for the AXFR QTYPE (see section 2.1.2 below for more details).
Section 4.2 of RFC 1035 discusses the transport layer use of DNS and Section 4.2 of RFC 1035 discusses the transport layer use of DNS and
shortly explains why UDP transport is deemed inappropriate for AXFR; shortly explains why UDP transport is deemed inappropriate for AXFR;
the last paragraph of Section 4.2.2 gives details for the TCP the last paragraph of Section 4.2.2 gives details for the TCP
connection management with AXFR. Finally, the second paragraph of connection management with AXFR. Finally, the second paragraph of
Section 6.3 in RFC 1035 mandates server behavior when zone data Section 6.3 in RFC 1035 mandates server behavior when zone data
changes occur during an ongoing zone transfer using AXFR. changes occur during an ongoing zone transfer using AXFR.
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specifying the record formats and processing rules for AXFR, largely specifying the record formats and processing rules for AXFR, largely
expanding on paragraph 5 of Section 4.3.5 of RFC 1034, and detailing expanding on paragraph 5 of Section 4.3.5 of RFC 1034, and detailing
the transport considerations for AXFR, thus amending Section 4.2.2 of the transport considerations for AXFR, thus amending Section 4.2.2 of
RFC 1035. Furthermore, it discusses backward compatibility issues RFC 1035. Furthermore, it discusses backward compatibility issues
and provides policy/management considerations as well as specific and provides policy/management considerations as well as specific
Security Considerations for AXFR. The goal of this document is to Security Considerations for AXFR. The goal of this document is to
define AXFR as it exists, or is supposed to exist, currently. define AXFR as it exists, or is supposed to exist, currently.
2 AXFR Messages 2 AXFR Messages
An AXFR message exchange (or session) consists of an AXFR query message An AXFR session consists of an exchange of a AXFR query message and a
and a set of AXFR response messages. In this document, AXFR client is set of AXFR response messages. In this document, the AXFR client is
the sender of the AXFR query and the AXFR server is the responder. the sender of the AXFR query and the AXFR server is the responder.
(Use of terms such as master, slave, primary, secondary are not (Use of terms such as master, slave, primary, secondary are not
important to defining the AXFR exchange.) The reason for the imbalance important to defining AXFR.) The use of the word "session" without
in number of messages derives from large zones whose contents cannot be qualification refers to an AXFR session.
fit into the limited permissible size of a DNS message.
An important aspect to keep in mind is that the definition of AXFR is An important aspect to keep in mind is that the definition of AXFR is
restricted to TCP [RFC0793]. The design of the AXFR process has restricted to TCP [RFC0793]. The design of the AXFR process has
certain inherent features that are not easily ported to UDP [RFC0768]. certain inherent features that are not easily ported to UDP [RFC0768].
The basic format of an AXFR message is the DNS message as defined in The basic format of an AXFR message is the DNS message as defined in
RFC 1035, Section 4 ("MESSAGES") [RFC1035], updated by the following: RFC 1035, Section 4 ("MESSAGES") [RFC1035], updated by the following:
- "A Mechanism for Prompt Notification of Zone Changes (...)" [RFC1996] - "A Mechanism for Prompt Notification of Zone Changes (...)" [RFC1996]
- "Domain Name System (DNS) IANA Considerations" [RFC2929] - "Domain Name System (DNS) IANA Considerations" [RFC5395]
- "Dynamic Updates in the Domain Name System (DNS UPDATE)" [RFC2136] - "Dynamic Updates in the Domain Name System (DNS UPDATE)" [RFC2136]
- "Extension Mechanisms for DNS (EDNS0)" [RFC2671] - "Extension Mechanisms for DNS (EDNS0)" [RFC2671]
- "Secret Key Transaction Authentication for DNS (TSIG)" [RFC2845] - "Secret Key Transaction Authentication for DNS (TSIG)" [RFC2845]
- "Secret Key Establishment for DNS (TKEY RR)" [RFC2930] - "Secret Key Establishment for DNS (TKEY RR)" [RFC2930]
- "Obsoleting IQUERY" [RFC3425] - "Obsoleting IQUERY" [RFC3425]
- "Handling of Unknown DNS Resource Record (RR) Types" [RFC3597] - "Handling of Unknown DNS Resource Record (RR) Types" [RFC3597]
- "Protocol Modifications for the DNS Security Extensions" [RFC4035] - "Protocol Modifications for the DNS Security Extensions" [RFC4035]
- "HMAC SHA TSIG Algorithm Identifiers" [RFC4635] - "HMAC SHA TSIG Algorithm Identifiers" [RFC4635]
The upper limit on the permissible size of a DNS message over TCP is The upper limit on the permissible size of a DNS message over TCP is
defined in RFC 1035, section 4.2.2. Unlike DNS messages over UDP, only restricted by the TCP framing defined in RFC 1035, section 4.2.2
this limit is not changed by EDNS0. which specifies a two-octet message length field, understood to be
unsigned, and thus causing a limit of 65535 octets. Unlike DNS
messages over UDP, this limit is not changed by EDNS0.
Field names used in this document will correspond to the names as they Field names used in this document will correspond to the names as they
appear in the IANA registry for DNS Header Flags [DNSFLGS]. appear in the IANA registry for DNS Header Flags [DNSFLGS].
2.1 AXFR query 2.1 AXFR query
An AXFR query is sent by a client whenever there is a reason to ask. An AXFR query is sent by a client whenever there is a reason to ask.
This might be because of zone maintenance activities or as a result of This might be because of zone maintenance activities or as a result of
a command line request, say for debugging. a command line request, say for debugging.
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support a particular mechanism, the client SHOULD NOT attempt to engage support a particular mechanism, the client SHOULD NOT attempt to engage
the server using the mechanism (or at all). A client could become the server using the mechanism (or at all). A client could become
aware of a server's abilities via a configuration setting or via some aware of a server's abilities via a configuration setting or via some
other (as yet) undefined means. other (as yet) undefined means.
The range of permissible resource records that MAY appear in the The range of permissible resource records that MAY appear in the
additional section might change over time. If either a change to an additional section might change over time. If either a change to an
existing resource record (like the OPT RR for EDNS0) is made or existing resource record (like the OPT RR for EDNS0) is made or
a new additional section record is created, the new definitions ought a new additional section record is created, the new definitions ought
to include a discussion on the impact upon AXFR. Although this is not to include a discussion on the impact upon AXFR. Although this is not
predictale, future additional section residing records may have an predictable, future additional section residing records may have an
effect that is orthogonal to AXFR, so can ride through the session as effect that is orthogonal to AXFR, so can ride through the session as
opaque data. In this case, a "wise" implementation ought to be able opaque data. In this case, a "wise" implementation ought to be able
to pass these records through without disruption. to pass these records through without disruption.
2.2 AXFR response 2.2 AXFR response
The AXFR response will consist of 0 or more messages. A "0 message" The AXFR response will consist of 0 or more messages. A "0 message"
response is covered in section 2.2.1. response is covered in section 2.2.1.
An AXFR response that is transferring the zone's contents will consist An AXFR response that is transferring the zone's contents will consist
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An AXFR response that is indicating an error MUST consist of a single An AXFR response that is indicating an error MUST consist of a single
DNS message with the return code set to the appropriate value for the DNS message with the return code set to the appropriate value for the
condition encountered - once the error condition is detected. Such condition encountered - once the error condition is detected. Such
a message MUST copy the AXFR query Query Section into its Query a message MUST copy the AXFR query Query Section into its Query
Section. The inclusion of the terminating SOA resource record is not Section. The inclusion of the terminating SOA resource record is not
necessary. necessary.
An AXFR client might receive a number of AXFR response messages An AXFR client might receive a number of AXFR response messages
free of an error condition before the message indicating an error free of an error condition before the message indicating an error
is received. But once an error is reported, the AXFR client can is received. But once an error is reported, the AXFR client can
assume that the error reporting message is the last. assume that the error reporting message is the last message sent by
the AXFR server in the current AXFR session.
2.2.1 "0 Message" Response 2.2.1 "0 Message" Response
A legitimate "0 message" response, i.e., the client sees no response A legitimate "0 message" response, i.e., the client sees no response
whatsoever, is very exceptional and controversial. Unquestionably it whatsoever, is very exceptional and controversial. Unquestionably it
is unhealthy for there to be 0 responses in a protocol that is designed is unhealthy for there to be 0 responses in a protocol that is designed
around a query - response paradigm over an unreliable transport. The around a query - response paradigm over an unreliable transport. The
lack of a response could be a sign of underlying network problems and lack of a response could be a sign of underlying network problems and
cause the protocol state machine to react accordingly. However, AXFR cause the protocol state machine to react accordingly. However, AXFR
uses TCP and not UDP, eliminating undetected network errors. uses TCP and not UDP, eliminating undetectable network errors.
A "0 message response" is reserved for situations in which the server A "0 message response" is reserved for situations in which the server
has a reason to suspect that the query is sent for the purpose of has a reason to suspect that the query is sent for the purpose of
abuse. Due to the use of this being so controversial, a "0 message abuse. Due to the use of this being so controversial, a "0 message
response" is not being defined as a legitimate part of the protocol response" is not being defined as a legitimate part of the protocol
but the use of it is being acknowledge as a warning to AXFR client but the use of it is being acknowledged as a warning to AXFR client
implementations. Any earnest query has the expectation of some implementations. Any earnest query has the expectation of some
response but may not get one. response but may not get one.
If an AXFR client sends a query on a TCP connection and the connection
is closed at any point, the AXFR client MUST consider the session
terminated. The message ID MAY be used again on a new connection,
even if the question and AXFR server are the same. Facing a dropped
connection a client SHOULD try to make some determination whether the
connection closure was the result of network activity or a decision
by the AXFR server. This determination is not an exact science. It
is up to the AXFR client implementor to react, but the reaction
SHOULD NOT be an endless cycle of retires nor an increasing (in
frequency) retry rate.
An AXFR server implementor SHOULD take into consideration what this
dilemma described above when a connection is closed with an outstanding
query in the pipeline. For this reason, a server ought to reserve
this course of action for situations in which it believes beyond a
doubt that the AXFR client is attemping abusive behavior.
2.2.2 Header Values 2.2.2 Header Values
ID See note 2.2.2.a ID See note 2.2.2.a
QR MUST be 1 (Response) QR MUST be 1 (Response)
OPCODE MUST be 0 (Standard Query) OPCODE MUST be 0 (Standard Query)
AA See note 2.2.2.b AA See note 2.2.2.b
TC MUST be 0 (Not truncated) TC MUST be 0 (Not truncated)
RD RECOMMENDED copy request's value, MAY be set to 0 RD RECOMMENDED copy request's value, MAY be set to 0
RA See note 2.2.2.c RA See note 2.2.2.c
Z See note 2.2.2.d Z See note 2.2.2.d
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message, then the value MUST be 1. A server MAY be made aware of a message, then the value MUST be 1. A server MAY be made aware of a
client's limitations via configuration data. client's limitations via configuration data.
Note 2.2.2.h The client MUST set this field to be the number of Note 2.2.2.h The client MUST set this field to be the number of
resource records appearing in the additional section. See Section resource records appearing in the additional section. See Section
2.1.5 "Additional Section" for details. 2.1.5 "Additional Section" for details.
2.2.3 Query Section 2.2.3 Query Section
In the first response message, this section MUST be copied from the In the first response message, this section MUST be copied from the
query. In subsequent messages this section MAY be copied from the query. In subsequent messages, this section MAY be copied from the
query, MAY be empty. The content of this section MAY be used to query or it MAY be empty. The content of this section MAY be used to
determine the context of the message, that is, the name of the zone determine the context of the message, that is, the name of the zone
being transferred. being transferred.
>| [...]. In subsequent messages, this section MAY be copied from the
>| query, or it MAY be empty. [...]
2.2.4 Answer Section 2.2.4 Answer Section
MUST be populated with the zone contents. See later section on MUST be populated with the zone contents. See later section on
encoding zone contents. encoding zone contents.
2.2.5 Authority Section 2.2.5 Authority Section
MUST be empty. MUST be empty.
2.2.5 Additional Section 2.2.6 Additional Section
The contents of this section MUST follow the guidelines for EDNS0, The contents of this section MUST follow the guidelines for EDNS0,
TSIG, SIG(0), or what ever other future record is possible here. The TSIG, SIG(0), or what ever other future record is possible here. The
contents of section 2.1.5 apply here as well. contents of section 2.1.5 apply here as well.
Note that TSIG and SIG(0), if in use, will treat each individual Note that TSIG and SIG(0), if in use, will treat each individual
AXFR response message within a session as a unit of data. That is, AXFR response message within a session as a unit of data. That is,
each message will have a TSIG or SIG(0) (if in use) and the each message will have a TSIG or SIG(0) (if in use) and the
crytpographic check will cover just that message. The same rule cryptographic check will cover just that message. The same rule
will apply to future alternatives and documents covering them ought will apply to future alternatives and documents covering them ought
to consider the impact on AXFR response messages. to consider the impact on AXFR response messages.
2.3 TCP Connection Aborts
If an AXFR client sends a query on a TCP connection and the connection
is closed at any point, the AXFR client MUST consider the AXFR session
terminated. The message ID MAY be used again on a new connection,
even if the question and AXFR server are the same. Facing a dropped
connection a client SHOULD try to make some determination whether the
connection closure was the result of network activity or a decision
by the AXFR server. This determination is not an exact science. It
is up to the AXFR client implementor to react, but the reaction
SHOULD NOT be an endless cycle of retries nor an increasing (in
frequency) retry rate.
An AXFR server implementor SHOULD take into consideration the dilemma
described above when a connection is closed with an outstanding query
in the pipeline. For this reason, a server ought to reserve this
course of action for situations in which it believes beyond a doubt
that the AXFR client is attempting abusive behavior.
3 Zone Contents 3 Zone Contents
The objective of the AXFR session is to request and transfer the The objective of the AXFR session is to request and transfer the
contents of a zone. The objective is to permit the client to contents of a zone. The objective is to permit the client to
reconstruct the zone as it exists at the server for the given zone reconstruct the zone as it exists at the server for the given zone
serial number. Over time the definition of a zone has evolved from a serial number. Over time the definition of a zone has evolved from a
static set of records to a dynamically updated set of records to a static set of records to a dynamically updated set of records to a
continually regenerated set of records. continually regenerated set of records.
3.1 Records to Include 3.1 Records to Include
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the database is divided into zones", and in particular, section 4.2.1, the database is divided into zones", and in particular, section 4.2.1,
"Technical considerations". "Technical considerations".
Unless the AXFR server knows that the AXFR client expects just one Unless the AXFR server knows that the AXFR client expects just one
resource record per AXFR response message, an AXFR server SHOULD resource record per AXFR response message, an AXFR server SHOULD
populate an AXFR response message with as many complete resource populate an AXFR response message with as many complete resource
records as will fit within a DNS message. records as will fit within a DNS message.
Zones for which it is impractical to list the entire zones for a serial Zones for which it is impractical to list the entire zones for a serial
number (because changes happen too quickly) are not suitable for AXFR number (because changes happen too quickly) are not suitable for AXFR
retrieval. retrieval. A typical (but not limiting) description of such a zone
is a zone consisting of responses generated via other database lookups
and/or computed based upon ever changing data. In essence, if the
zone changes (on average) more frequently than and AXFR session can be
finished, the zone is not a good candidate for AXFR.
3.2 Delegation Records 3.2 Delegation Records
In RFC 1034, section 4.2.1, this text appears (keep in mind that the In RFC 1034, section 4.2.1, this text appears (keep in mind that the
"should" in the quotation predates [BCP14], cf. section 1.1) "The RRs "should" in the quotation predates [BCP14], cf. section 1.1) "The RRs
that describe cuts ... should be exactly the same as the corresponding that describe cuts ... should be exactly the same as the corresponding
RRs in the top node of the subzone." There has been some controversy RRs in the top node of the subzone." There has been some controversy
over this statement and the impact on which NS resource records are over this statement and the impact on which NS resource records are
included in a zone transfer. included in a zone transfer.
The phrase "that describe cuts" is a reference to the NS set and The phrase "that describe cuts" is a reference to the NS set and
applicable glue records. It does not mean that the cut points and the applicable glue records. It does not mean that the cut points and the
apex resource records are identical. For example, the SOA resource apex resource records are identical. For example, the SOA resource
record is only found at the apex, as well as a slew of DNSSEC resource record is only found at the apex, as well as DNSSEC resource records.
records. There are also some DNSSEC resource record sets that are The is even a DNSSEC resource record found only at the zone cut and not
explicitly different between the cut point and the apex. The at the corresponding apex. There are also some DNSSEC resource record
discussion here is restricted to just the NS resource record set and sets that are explicitly different between the cut point and the apex.
glue as these "describe cuts." The discussion here is restricted to just the NS resource record set
and glue as these "describe cuts."
The issue is that in operations there are times when the NS resource The issue is that in operations there are times when the NS resource
records for a zone might be different at a cut point in the parent and records for a zone might be different at a cut point in the parent and
at the apex of a zone. Sometimes this is the result of an error and at the apex of a zone. Sometimes this is the result of an error and
sometimes it is part of an ongoing change in name servers. The DNS sometimes it is part of an ongoing change in name servers. The DNS
protocol is robust enough to overcome inconsistencies up to (but not protocol is robust enough to overcome inconsistencies up to (but not
including) there being no parent indicated NS resource record including) there being no parent indicated NS resource record
referencing a server that is able to serve the child zone. This referencing a server that is able to serve the child zone. This
robustness is one quality that has fueled the success of the DNS. robustness is one quality that has fueled the success of the DNS.
Still, the inconsistency is a error state and steps need to be taken Still, the inconsistency is an error state and steps need to be taken
to make it apparent (if it is unplanned) and to make it clear once to make it apparent (if it is unplanned) and to make it clear once
the inconsistency has been removed. the inconsistency has been removed.
Another issue is that the AXFR server could be authoritative for a Another issue is that the AXFR server could be authoritative for a
different set of zones than the AXFR client. It is possible that the different set of zones than the AXFR client. It is possible that the
AXFR server be authoritative for both halves of an inconsistent cut AXFR server be authoritative for both halves of an inconsistent cut
point and that the AXFR client is authoritative for just the parent of point and that the AXFR client is authoritative for just the parent of
the cut point. the cut point.
The question that arises is, when facing a situation in which a cut The question that arises is, when facing a situation in which a cut
point's NS resource records do not match the authoritative set, whether point's NS resource records do not match the authoritative set, whether
an AXFR server responds with the NS resource record set that is in the an AXFR server responds with the NS resource record set that is in the
zone or is at the authoritative location. zone being transferred or is at the authoritative location.
The AXFR response MUST contain the cut point NS resource record set The AXFR response MUST contain the cut point NS resource record set
registered with the zone whether it agrees with the authoritative set registered with the zone whether it agrees with the authoritative set
or not. "Registered with" can be widely interpreted to include data or not. "Registered with" can be widely interpreted to include data
residing in the zone file of the zone for the particular serial residing in the zone file of the zone for the particular serial
number (in zone file environments) or as any data configured to be in number (in zone file environments) or as any data configured to be in
the zone (database), statically or dynamically. the zone (database), statically or dynamically.
The reasons for this requirement are: The reasons for this requirement are:
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an authorized administrator can manually request the AXFR and inspect an authorized administrator can manually request the AXFR and inspect
the results to see the inconsistent records. (A server authoritative the results to see the inconsistent records. (A server authoritative
for both halves would otherwise always answer from the more for both halves would otherwise always answer from the more
authoritative set, concealing the error.) authoritative set, concealing the error.)
3) The inconsistent NS resource record set might indicate a problem 3) The inconsistent NS resource record set might indicate a problem
in a registration database. in a registration database.
4) Beginning with an error state of two servers for a zone having 4) Beginning with an error state of two servers for a zone having
inconsistent zone contents for a given zone serial number, if a client inconsistent zone contents for a given zone serial number, if a client
requests and recieves an IXFR transfer from one server followed by requests and receives an IXFR transfer from one server followed by
another IXFR transfer from the other server, the client can encounter another IXFR transfer from the other server, the client can encounter
an IXFR protocol error state where an attempt is made to incrementally an IXFR protocol error state where an attempt is made to incrementally
add a record that already exists or to delete a record that does not add a record that already exists or to delete a record that does not
exist. exist.
(Editorial note, the 4th reason was suggested, but I don't see how (Editorial note, the 4th reason was suggested, but I don't see how
it relates. A nudge for updated text on this.) it relates. A nudge for updated text on this.)
3.3 Glue Records 3.3 Glue Records
As quoted in the previous section, RFC 1034, section 4.2.1, provides As quoted in the previous section, section 4.2.1 of RFC 1034 provides
guidance and rationale for the inclusion of glue records as part of guidance and rationale for the inclusion of glue records as part of
an AXFR transfer. And, as also argued in the previous section of this an AXFR transfer. And, as also argued in the previous section of this
document, even when there is an inconsistency between the address in a document, even when there is an inconsistency between the address in a
glue record and the authoritative copy of the name server's address, glue record and the authoritative copy of the name server's address,
the glue resource record that is registered as part of the zone for the glue resource record that is registered as part of the zone for
that serial number is to be included. that serial number is to be included.
This applies for glue records for any address family. This applies to glue records for any address family [RFC1700].
The AXFR response MUST contain the appropriate glue records as The AXFR response MUST contain the appropriate glue records as
registered with the zone. The interpretation of "registered with" registered with the zone. The interpretation of "registered with"
in the previous section applies here. Inconsistent glue records are in the previous section applies here. Inconsistent glue records are
an operational matter. an operational matter.
3.4 Name Compression 3.4 Name Compression
Compression of names in DNS messages is described in RFC 1035, section Compression of names in DNS messages is described in RFC 1035, section
4.1.4, "Message compression". The issue highlighted here relates to a 4.1.4, "Message compression". The issue highlighted here relates to a
skipping to change at line 617 skipping to change at line 636
of name comparison in the DNS protocol and represents a new of name comparison in the DNS protocol and represents a new
requirement on AXFR servers. requirement on AXFR servers.
Rules governing name compression of RDATA in an AXFR message MUST Rules governing name compression of RDATA in an AXFR message MUST
abide by the specification in "Handling of Unknown DNS Resource Record abide by the specification in "Handling of Unknown DNS Resource Record
(RR) Types" [RFC3597], specifically, section 4 on "Domain Name (RR) Types" [RFC3597], specifically, section 4 on "Domain Name
Compression." Compression."
3.5 Occluded Names 3.5 Occluded Names
Dynamic Update [RFC2136] (and including DNAME [2672]) operations can Dynamic Update [RFC2136] (and including DNAME [RFC2672]) operations can
have a side effect of occluding names in a zone. The addition of a have a side effect of occluding names in a zone. The addition of a
delegation point via dynamic update will render all subordinate domain delegation point via dynamic update will render all subordinate domain
names to be in a limbo, still part of the zone but not available for to names to be in a limbo, still part of the zone but not available
the look up process. The addition of a DNAME resource record set has to the lookup process. The addition of a DNAME resource record has the
the same impact. The subordinate names are said to be "occluded." same impact. The subordinate names are said to be "occluded."
Occluded names MUST be included in AXFR responses. An AXFR client MUST Occluded names MUST be included in AXFR responses. An AXFR client MUST
be able to identify and handle occluded names. The rationale for this be able to identify and handle occluded names. The rationale for this
action is based on a speedy recovery if the dynamic update operation action is based on a speedy recovery if the dynamic update operation
was in error and is to be undone. was in error and is to be undone.
4 Transport 4 Transport
AXFR sessions are currently restricted to TCP by section 4.3.5 of RFC AXFR sessions are currently restricted to TCP by section 4.3.5 of RFC
1034 that states: "Because accuracy is essential, TCP or some other 1034 that states: "Because accuracy is essential, TCP or some other
reliable protocol must be used for AXFR requests." The most common reliable protocol must be used for AXFR requests." The restriction to
scenario is for an AXFR client to open a TCP connection to the AXFR TCP is also mentioned in section 6.1.3.2. of "Requirements for Internet
server, send an AXFR query, receive the AXFR response, and then Hosts - Application and Support" [RFC1123].
close the connection. There are variations on this, such as a query
for the zone's SOA resource record first, and so on.
Two issues have emerged since the original specification of AXFR. The most common scenario is for an AXFR client to open a TCP connection
One is that lack of specificity has yielded some implementations to the AXFR server, send an AXFR query, receive the AXFR response, and
that assume the TCP connection is dedicated to the single AXFR then close the connection. There are variations on this, such as a
session, which has led to implementation choices that prevent either query for the zone's SOA resource record first, and so on. Note that
multiple concurrent zone transfers or the use of the open connection this is documented as a most common scenario.
for other queries. The other issue is the prospect of using UDP as a
transport has come to look promising because of trends in the past The assumption that a TCP connection is dedicated to the single AXFR
two decades. session is incorrect, this as has led to implementation choices that
prevent either multiple concurrent zone transfers or the use of the
open connection for other queries.
Being able to have multiple concurrent zone transfers is considered Being able to have multiple concurrent zone transfers is considered
desirable by operators who have sets of name servers that are desirable by operators who have sets of name servers that are
authoritative for a common set of zones. It would be desirable authoritative for a common set of zones. It would be desirable
if the name server implementations did not have to wait for one if the name server implementations did not have to wait for one
zone to transfer before the next could begin. The desire here is to zone to transfer before the next could begin. The desire here is to
tighten the specification, not a change, but adding words to the tighten the specification, not a change, but adding words to the
unclear areas, to define what is needed to permit two servers to unclear areas, to define what is needed to permit two servers to
share a TCP connection among concurrent AXFR sessions. The challenge share a TCP connection among concurrent AXFR sessions. The challenge
is to design this in a way that can fall back to the old behavior if is to design this in a way that can fall back to the old behavior if
skipping to change at line 692 skipping to change at line 711
AXFR server ought to induce the server to operate within the AXFR server ought to induce the server to operate within the
specification for an older server. specification for an older server.
4.1.1 AXFR client TCP 4.1.1 AXFR client TCP
An AXFR client MAY request an connection to an AXFR server for any An AXFR client MAY request an connection to an AXFR server for any
reason. An AXFR client SHOULD close the connection when there is reason. An AXFR client SHOULD close the connection when there is
no apparent need to use the connection for some time period. The no apparent need to use the connection for some time period. The
AXFR server ought not have to maintain idle connections, the burden AXFR server ought not have to maintain idle connections, the burden
of connection closure ought to be on the client. Apparent need for of connection closure ought to be on the client. Apparent need for
the connection is a judgement for the AXFR client and the DNS the connection is a judgment for the AXFR client and the DNS
client. If the connection is used for multiple sessions, or it is client. If the connection is used for multiple sessions, or if it is
known sessions will be coming or is there is other query/response known sessions will be coming or if there is other query/response
traffic on the open connection, that is "apparent need." traffic anticipated or currently on the open connection, then there
is "apparent need."
An AXFR client MAY cancel delivery of a zone only by closing the An AXFR client MAY cancel delivery of a zone only by closing the
connection. However, this action will also cancel all other outstanding connection. However, this action will also cancel all other outstanding
activity using the connection. There is no other mechanism by which activity using the connection. There is no other mechanism by which
an AXFR response can be cancelled. an AXFR response can be cancelled.
When a TCP connection is closed remotely (relative to the client), When a TCP connection is closed remotely (relative to the client),
whether by the AXFR server or due to a network event, the AXFR client whether by the AXFR server or due to a network event, the AXFR client
MUST cancel all outstanding sessions. Recovery from this situation MUST cancel all outstanding sessions. Recovery from this situation
is not straightforward. If the disruption was a spurious event, is not straightforward. If the disruption was a spurious event,
skipping to change at line 721 skipping to change at line 741
the AXFR client would be wise to not retry the connection. the AXFR client would be wise to not retry the connection.
Unfortunately, knowing which of the three cases above applies is not Unfortunately, knowing which of the three cases above applies is not
clear (momentary disruption, failure, policy). clear (momentary disruption, failure, policy).
An AXFR client MAY use an already opened TCP connection to start an An AXFR client MAY use an already opened TCP connection to start an
AXFR session. Using an existing open connection is RECOMMENDED over AXFR session. Using an existing open connection is RECOMMENDED over
opening a new connection. (Non-AXFR session traffic can also use an opening a new connection. (Non-AXFR session traffic can also use an
open connection.) If in doing so the AXFR client realizes that open connection.) If in doing so the AXFR client realizes that
the responses cannot be properly differentiated (lack of matching the responses cannot be properly differentiated (lack of matching
query IDs for example) or the connection is terminated for a remote query IDs for example) or the connection is terminated for a remote
reason, then the AXFR client SHOULD not attempt to reuse an open reason, then the AXFR client SHOULD NOT attempt to reuse an open
connection with the specific AXFR server until the AXFR server is connection with the specific AXFR server until the AXFR server is
updated (which is of course, not an event captured in the DNS updated (which is of course, not an event captured in the DNS
protocol). protocol).
4.1.2 AXFR server TCP 4.1.2 AXFR server TCP
An AXFR server MUST be able to handle multiple AXFR sessions on a An AXFR server MUST be able to handle multiple AXFR sessions on a
single TCP connection, as well as handle other query/response sessions. single TCP connection, as well as handle other query/response sessions.
If a TCP connection is closed remotely, the AXFR server MUST cancel If a TCP connection is closed remotely, the AXFR server MUST cancel
skipping to change at line 760 skipping to change at line 780
A zone administrator has the option to restrict AXFR access to a zone. A zone administrator has the option to restrict AXFR access to a zone.
This was not envisioned in the original design of the DNS but has This was not envisioned in the original design of the DNS but has
emerged as a requirement as the DNS has evolved. Restrictions on AXFR emerged as a requirement as the DNS has evolved. Restrictions on AXFR
could be for various reasons including a desire (or in some instances, could be for various reasons including a desire (or in some instances,
having a legal requirement) to keep the bulk version of the zone having a legal requirement) to keep the bulk version of the zone
concealed or to prevent the servers from handling the load incurred in concealed or to prevent the servers from handling the load incurred in
serving AXFR. All reasons are arguable, but the fact remains that serving AXFR. All reasons are arguable, but the fact remains that
there is a requirement to provide mechanisms to restrict AXFR. there is a requirement to provide mechanisms to restrict AXFR.
A DNS implementation SHOULD provide means to restrict AXFR sessions to A DNS implementation SHOULD provide means to restrict AXFR sessions to
specific clients. By default, a DNS implementation SHOULD only allow specific clients.
the designated authoritative servers to have access to the zone.
An implementation SHOULD allow access to be granted to Internet An implementation SHOULD allow access to be granted to Internet
Protocol addresses and ranges, regardless of whether a source address Protocol addresses and ranges, regardless of whether a source address
could be spoofed. Combining this with techniques such as Virtual could be spoofed. Combining this with techniques such as Virtual
Private Networks (VPN) [RFC2764] or Virtual LANs has proven to be Private Networks (VPN) [RFC2764] or Virtual LANs has proven to be
effective. effective.
A general purpose implementation is RECOMMENDED to implement access A general purpose implementation is RECOMMENDED to implement access
controls based upon "Secret Key Transaction Authentication for DNS" controls based upon "Secret Key Transaction Authentication for DNS"
[RFC2845] and/or "DNS Request and Transaction Signatures ( SIG(0)s )" [RFC2845] and/or "DNS Request and Transaction Signatures ( SIG(0)s )"
[RFC2931]. [RFC2931].
A general purpose implementation SHOULD allow access to be open to A general purpose implementation SHOULD allow access to be open to
all AXFR requests. I.e., an operator ought to be able to allow any all AXFR requests. I.e., an operator ought to be able to allow any
AXFR query to be granted. AXFR query to be granted.
A general purpose implementation SHOULD NOT have a default policy A general purpose implementation SHOULD NOT have a default policy
for AXFR requests to be "open to all." for AXFR requests to be "open to all." For example, a default could
be to restrict transfers to loopback address(es) and such.
6 Zone Integrity 6 Zone Integrity
An AXFR client MUST ensure that only a successfully transferred
copy of the zone data can be used to serve this zone. Previous
description and implementation practice have introduced a two-stage
model of the whole zone synchronization procedure: Upon a trigger
event (e.g., polling of SOA resource record detects change in the
SOA serial number, or via DNS NOTIFY [RFC1996]), the AXFR session
is initiated, whereby the zone data are saved in a zone file or
data base (this latter step is necessary anyway to ensure proper
restart of the server); upon successful completion of the AXFR
operation and some sanity checks, this data set is 'loaded' and
made available for serving the zone in an atomic operation, and
flagged 'valid' for use during the next restart of the DNS server;
if any error is detected, this data set MUST be deleted, and the
AXFR client MUST continue to serve the previous version of the zone,
if it did before. The externally visible behavior of an AXFR client
implementation MUST be equivalent to that of this two-stage model.
If a server rejects data contained in an AXFR session, the server
SHOULD remember the serial number and not attempt to retrieve the
same zone version again.
Ensuring that an AXFR client does not accept a forged copy of a zone is Ensuring that an AXFR client does not accept a forged copy of a zone is
important to the security of a zone. If a zone operator has the important to the security of a zone. If a zone operator has the
opportunity, protection can be afforded via dedicated links, physical opportunity, protection can be afforded via dedicated links, physical
or virtual via a VPN among the authoritative servers. But there are or virtual via a VPN among the authoritative servers. But there are
instances in which zone operators have no choice but to run AXFR instances in which zone operators have no choice but to run AXFR
sessions over the global public Internet. sessions over the global public Internet.
Besides best attempts at securing TCP sessions, DNS implementations Besides best attempts at securing TCP sessions, DNS implementations
SHOULD provide means to make use of "Secret Key Transaction SHOULD provide means to make use of "Secret Key Transaction
Authentication for DNS" [RFC2845] and/or "DNS Request and Transaction Authentication for DNS" [RFC2845] and/or "DNS Request and Transaction
Signatures ( SIG(0)s )" [RFC2931] to allow AXFR clients to verify the Signatures ( SIG(0)s )" [RFC2931] to allow AXFR clients to verify the
contents. These techniques MAY also be used for authorization. contents. These techniques MAY also be used for authorization.
7 Backwards Compatibility 7 Zone Expiry Timer
Section 4.3.5 of RFC 1034 contains the following paragraph:
"The periodic polling of the secondary servers is controlled by
parameters in the SOA RR for the zone, which set the minimum acceptable
polling intervals. The parameters are called REFRESH, RETRY, and
EXPIRE. Whenever a new zone is loaded in a secondary, the secondary
waits REFRESH seconds before checking with the primary for a new serial.
If this check cannot be completed, new checks are started every RETRY
seconds. The check is a simple query to the primary for the SOA RR of
the zone. If the serial field in the secondary's zone copy is equal to
the serial returned by the primary, then no changes have occurred, and
the REFRESH interval wait is restarted. If the secondary finds it
impossible to perform a serial check for the EXPIRE interval, it must
assume that its copy of the zone is obsolete an discard it."
Perhaps what is not clear in the paragraph regarding the EXPIRE
interval timer is that it is only reset to the EXPIRE parameter when
a new zone is loaded. A new zone means a zone with a higher serial
number than the most recently loaded zone. The EXPIRE interval timer
is not reset automatically as a result of a zone transfer as a zone
could be (mistakenly) transferred with the same or lower serial number.
I.e., successively transferring a zone from server to server does not
permit the zone to avoid expiration.
8 Backwards Compatibility
Describing backwards compatibility is difficult because of the lack of Describing backwards compatibility is difficult because of the lack of
specifics in the original definition. In this section some hints at specifics in the original definition. In this section some hints at
building in backwards compatibility are given, mostly repeated from the building in backwards compatibility are given, mostly repeated from the
earlier sections. earlier sections.
Backwards compatibility is not necessary, but the greater extent of an Backwards compatibility is not necessary, but the greater extent of an
implementation's compatibility increases it's interoperability. For implementation's compatibility increases it's interoperability. For
turnkey implementations this is not usually a concern. For general turnkey implementations this is not usually a concern. For general
purpose implementations this takes on varying levels of importance purpose implementations this takes on varying levels of importance
depending on the implementer's desire to maintain interoperability. depending on the implementer's desire to maintain interoperability.
It is unfortunate that a need to fall back to older behavior cannot be It is unfortunate that a need to fall back to older behavior cannot be
discovered, hence needs to be noted in a configuration file. An discovered, hence needs to be noted in a configuration file. An
implementation SHOULD, in it's documentation, encourage operators to implementation SHOULD, in it's documentation, encourage operators to
periodically review AXFR clients and servers it has made notes about as periodically review AXFR clients and servers it has made notes about as
old software periodically gets updated. old software periodically gets updated.
7.1 Server 8.1 Server
An AXFR server has the luxury of being able to react to an AXFR An AXFR server has the luxury of being able to react to an AXFR
client's abilities with the exception of knowing if the client can client's abilities with the exception of knowing if the client can
accept multiple resource records per AXFR response message. The accept multiple resource records per AXFR response message. The
knowledge that a client is so restricted apparently cannot be knowledge that a client is so restricted apparently cannot be
discovered, hence it has to be set by configuration. discovered, hence it has to be set by configuration.
An implementation of an AXFR server SHOULD permit configuring, on a per An implementation of an AXFR server SHOULD permit configuring, on a per
AXFR client basis, a need to revert to single resource record per AXFR client basis, a need to revert to single resource record per
message. The default SHOULD be to use multiple records per message. message. The default SHOULD be to use multiple records per message.
7.2 Client 8.2 Client
An AXFR client has the opportunity to try extensions when querying An AXFR client has the opportunity to try extensions when querying
an AXFR server. an AXFR server.
Attempting to issue multiple DNS queries over a TCP transport for an Attempting to issue multiple DNS queries over a TCP transport for an
AXFR session SHOULD be aborted if it interrupts the original request AXFR session SHOULD be aborted if it interrupts the original request
and SHOULD take into consideration whether the AXFR server intends to and SHOULD take into consideration whether the AXFR server intends to
close the connection immediately upon completion of the original close the connection immediately upon completion of the original
(connection-causing) zone transfer. (connection-causing) zone transfer.
8 Security Considerations 9 Security Considerations
Concerns regarding authorization, traffic flooding, and message Concerns regarding authorization, traffic flooding, and message
integrity are mentioned in "Authorization" (section 5), "TCP" (section integrity are mentioned in "Authorization" (section 5), "TCP" (section
4.2) and Zone Integrity (section 6). 4.2) and "Zone Integrity" (section 6).
9 IANA Considerations 10 IANA Considerations
No new registries or new registrations are included in this document. No new registries or new registrations are included in this document.
10 Internationalization Considerations 11 Internationalization Considerations
It is assumed that supporting of international domain names has been It is assumed that supporting of international domain names has been
solved via "Internationalizing Domain Names in Applications (IDNA)" solved via "Internationalizing Domain Names in Applications (IDNA)"
[RFC3490]. [RFC3490].
11 Acknowledgements 12 Acknowledgements
Earlier editions of this document have been edited by Andreas Earlier editions of this document have been edited by Andreas
Gustafsson. In his latest version, this acknowledgement appeared. Gustafsson. In his latest version, this acknowledgement appeared.
"Many people have contributed input and commentary to earlier versions "Many people have contributed input and commentary to earlier versions
of this document, including but not limited to Bob Halley, Dan of this document, including but not limited to Bob Halley, Dan
Bernstein, Eric A. Hall, Josh Littlefield, Kevin Darcy, Robert Elz, Bernstein, Eric A. Hall, Josh Littlefield, Kevin Darcy, Robert Elz,
Levon Esibov, Mark Andrews, Michael Patton, Peter Koch, Sam Trenholme, Levon Esibov, Mark Andrews, Michael Patton, Peter Koch, Sam Trenholme,
and Brian Wellington." and Brian Wellington."
Comments since the -05 version have come from these individuals: Comments since the -05 version have come from these individuals:
Alfred Hoenes, Mark Andrews, Paul Vixie, Wouter Wijngaards, Iain Alfred Hoenes, Mark Andrews, Paul Vixie, Wouter Wijngaards, Iain
Calder, Tony Finch, Ian Jackson, Andreas Gustafsson, Brian Wellington, Calder, Tony Finch, Ian Jackson, Andreas Gustafsson, Brian Wellington,
... ...
12 References 13 References
All references prefixed by "RFC" can be obtained from the RFC Editor, All references prefixed by "RFC" can be obtained from the RFC Editor
web site at the URLs: http://rfc-editor.org/rfc.html
or http://rfc-editor.org/rfcsearch.html ;
information regarding this organization can be found at the following information regarding this organization can be found at the following
URL: URL: http://rfc-editor.org/
http://rfc-editor.org/
Additionally, these documents can be obtained via the IETF web site.
12.1 Normative 13.1 Normative
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
September 1981. September 1981.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August
1980. 1980.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987. STD 13, RFC 1034, November 1987.
[RFC1035] Mockapetris, P., "Domain names - implementation and [RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987. specification", STD 13, RFC 1035, November 1987.
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application
and Support", STD 3, RFC 1123, October 1989.
[RFC1995] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995, [RFC1995] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,
August 1996. August 1996.
[RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone [RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone
Changes (DNS NOTIFY)", RFC 1996, August 1996. Changes (DNS NOTIFY)", RFC 1996, August 1996.
[RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC "Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC
2136, April 1997. 2136, April 1997.
[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC 2671, [RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC 2671,
August 1999. August 1999.
[RFC2672] Crawford, M., "Non-Terminal DNS Name Redirection", RFC 2672, [RFC2672] Crawford, M., "Non-Terminal DNS Name Redirection", RFC 2672,
August 1999. August 1999.
[RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B. [RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
Wellington, "Secret Key Transaction Authentication for DNS Wellington, "Secret Key Transaction Authentication for DNS
(TSIG)", RFC 2845, May 2000. (TSIG)", RFC 2845, May 2000.
[RFC2929] Eastlake 3rd, D., Brunner-Williams, E., and B. Manning, [RFC5395] Eastlake 3rd, "Domain Name System (DNS) IANA Considerations",
"Domain Name System (DNS) IANA Considerations", BCP 42, RFC BCP 42, RFC 5395, November 2008.
2929, September 2000.
[RFC2930] Eastlake 3rd, D., "Secret Key Establishment for DNS (TKEY [RFC2930] Eastlake 3rd, D., "Secret Key Establishment for DNS (TKEY
RR)", RFC 2930, September 2000. RR)", RFC 2930, September 2000.
[RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures [RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures
( SIG(0)s )", RFC 2931, September 2000. ( SIG(0)s )", RFC 2931, September 2000.
[RFC3425] Lawrence, D., "Obsoleting IQUERY", RFC 3425, November 2002. [RFC3425] Lawrence, D., "Obsoleting IQUERY", RFC 3425, November 2002.
[RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record [RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record
(RR) Types", RFC 3597, September 2003. (RR) Types", RFC 3597, September 2003.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", RFC 4033, Rose, "DNS Security Introduction and Requirements", RFC 4033,
March 2005. March 2005.
skipping to change at line 927 skipping to change at line 996
RFC 4034, March 2005. RFC 4034, March 2005.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, March 2005. Extensions", RFC 4035, March 2005.
[RFC4635] Eastlake 3rd, D., "HMAC SHA (Hashed Message Authentication [RFC4635] Eastlake 3rd, D., "HMAC SHA (Hashed Message Authentication
Code, Secure Hash Algorithm) TSIG Algorithm Identifiers", Code, Secure Hash Algorithm) TSIG Algorithm Identifiers",
RFC 4635, August 2006. RFC 4635, August 2006.
[DNSFLGS] http://www.iana.org/assignments/dns-header-flags [DNSFLGS] http://www.iana.org/assignments/dns-header-flags
[DNSVALS] http://www.iana.org/assignments/dns-parameters [DNSVALS] http://www.iana.org/assignments/dns-parameters
12.2 Informative 13.2 Informative
[BCP14] Bradner, S., "Key words for use in RFCs to Indicate [BCP14] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC1700] J. Reynolds and J. Postel, "Assigned Numbers", RFC 1700,
October 1994.
[RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A. [RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A.
Malis, "A Framework for IP Based Virtual Private Networks", Malis, "A Framework for IP Based Virtual Private Networks",
RFC 2764, February 2000. RFC 2764, February 2000.
[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)", RFC "Internationalizing Domain Names in Applications (IDNA)", RFC
3490, March 2003. 3490, March 2003.
13 Editor's Address 14 Editor's Address
Edward Lewis Edward Lewis
46000 Center Oak Plaza 46000 Center Oak Plaza
Sterling, VA, 22033, US Sterling, VA, 22033, US
+1-571-434-5468 +1-571-434-5468
ed.lewis@neustar.biz ed.lewis@neustar.biz
Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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The IETF takes no position regarding the validity or scope of any
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Copies of IPR disclosures made to the IETF Secretariat and any
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Acknowledgment Acknowledgment
Funding for the RFC Editor function is provided by the IETF Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA). Administrative Support Activity (IASA).
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