draft-ietf-dnsext-axfr-clarify-07.txt   draft-ietf-dnsext-axfr-clarify-08.txt 
INTERNET-DRAFT Edward Lewis INTERNET-DRAFT Edward Lewis
draft-ietf-dnsext-axfr-clarify-07.txt NeuStar, Inc. draft-ietf-dnsext-axfr-clarify-08.txt NeuStar, Inc.
DNSEXT WG February 2008
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)
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
skipping to change at line 30 skipping to change at line 30
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on September 1, 2008. This Internet-Draft will expire on December 1, 2008.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2008). Copyright (C) The IETF Trust (2008).
Abstract Abstract
The Domain Name System standard facilities for maintaining coherent The Domain Name System standard facilities for maintaining coherent
servers for a zone consist of three elements. The Authoritative servers for a zone consist of three elements. The Authoritative
Transfer (AXFR) is defined in RFC 1034 and RFC 1035. The Incremental Transfer (AXFR) is defined in RFC 1034 and RFC 1035. The Incremental
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AXFR mechanism. AXFR mechanism.
1 Introduction 1 Introduction
The Domain Name System standard facilities for maintaining coherent The Domain Name System standard facilities for maintaining coherent
servers for a zone consist of three elements. Authoritative servers for a zone consist of three elements. Authoritative
Transfer (AXFR) is defined in "Domain Names - Concepts and Facilities" Transfer (AXFR) is defined in "Domain Names - Concepts and Facilities"
[RFC1034] (referred to in this document as RFC 1034) and "Domain Names [RFC1034] (referred to in this document as RFC 1034) and "Domain Names
- Implementation and Specification" [RFC1035] (aka RFC 1035). - Implementation and Specification" [RFC1035] (aka RFC 1035).
Incremental Zone Transfer (IXFR) is defined in "Incremental Zone Incremental Zone Transfer (IXFR) is defined in "Incremental Zone
Transfer in DNS" [RFC1995]. A mechanism for prompt notification of zone Transfer in DNS" [RFC1995]. A mechanism for prompt notification of
changes (NOTIFY) is defined in "A Mechanism for Prompt Notification of zone changes (NOTIFY) is defined in "A Mechanism for Prompt
Zone Changes (DNS NOTIFY)" [RFC1996]. The goal of these mechanisms is Notification of Zone Changes (DNS NOTIFY)" [RFC1996]. The goal of
to enable a set of DNS name servers to remain coherently authoritative these mechanisms is to enable a set of DNS name servers to remain
for a given zone. coherently authoritative for a given zone.
Comments on this draft ought to be addressed to the editor or to Comments on this draft ought to be addressed to the editor or to
namedroppers@ops.ietf.org. namedroppers@ops.ietf.org.
1.1 Definition of Terms 1.1 Definition of Terms
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in "Key words for use in document are to be interpreted as described in "Key words for use in
RFCs to Indicate Requirement Levels" [BCP14]. RFCs to Indicate Requirement Levels" [BCP14].
"Newer"/"New DNS and "older"/"old" DNS refers to implementations "Newer"/"New" DNS and "older"/"old" DNS refers to implementations
written after and prior to the publication of this document. written after and prior to the publication of this document.
1.2 Scope 1.2 Scope
In the greater context, there are many ways to achieve coherency among a In the greater context there are many ways to achieve coherency among
set of name servers. These mechanisms form just one, the one defined in a set of name servers. The AXFR, IXFR and NOTIFY mechanisms form
the RFCs cited. For example, there are DNS implementations that just one, the one defined in the RFCs cited. For example, there are
assemble answers from data stored in commercial (as opposed to open DNS implementations that assemble answers from data stored in
source, etc.) database instances, and rely on the database's relational databases (as opposed to master files) relying on the
proprietary or otherwise external-to-DNS means to synchronize the database's non-DNS means to synchronize the database instances. Some
database instances. Some of these non-DNS solutions might even of these non-DNS solutions interoperate in some fashion. As far as
interoperate in some fashion. As far as it is known, AXFR, IXFR, and it is known, AXFR, IXFR and NOTIFY are the only mechanisms that
NOTIFY are the only mechanisms that provide an interoperable solution provide an interoperable solution to the desire for coherency within
to the desire for coherency within the definition of DNS, they the definition of DNS, they certainly are the only mechanisms
certainly are the only mechanisms documented by the IETF. documented by the IETF.
This document does not cover incoherent DNS situations. There are This document does not cover incoherent DNS situations. There are
applications of the DNS in which servers for a zone are designed to be applications of the DNS in which servers for a zone are designed to be
incoherent. For these configurations, a coherency mechanism as incoherent. For these configurations, a coherency mechanism as
described here would be unsuitable. described here would be unsuitable.
"General purpose DNS implementation" refers to DNS software developed "General purpose DNS implementation" refers to DNS software developed
for wide-spread use. This includes resolvers and servers freely for wide-spread use. This includes resolvers and servers freely
accessible as libraries and standalone processes. This also includes accessible as libraries and standalone processes. This also includes
proprietary implementations used only in support of DNS service proprietary implementations used only in support of DNS service
offerings. offerings.
"Turnkey DNS implementation" refers to custom made, single use "Turnkey DNS implementation" refers to custom made, single use
implementations of DNS. Such implementations consist of software implementations of DNS. Such implementations consist of software
that employes the DNS protocol message format yet do not conform to that employes the DNS protocol message format yet do not conform to
the entire range of DNS functionality. the entire range of DNS functionality.
A DNS implementation is not required to support AXFR, IXFR, and NOTIFY. A DNS implementation is not required to support AXFR, IXFR and NOTIFY.
A DNS implementation SHOULD have some means for maintaining name server A DNS implementation SHOULD have some means for maintaining name server
coherency. A general purpose DNS implementation SHOULD include AXFR, coherency. A general purpose DNS implementation SHOULD include AXFR,
IXFR, and NOTIFY, but turnkey DNS implementations MAY operate without IXFR and NOTIFY, but turnkey DNS implementations MAY operate without
it. it.
1.3 Context 1.3 Context
Besides describing the mechanisms themselves, there is the context in Besides describing the mechanisms themselves, there is the context in
which they operate to consider. When AXFR, IXFR, and NOTIFY were which they operate to consider. When AXFR, IXFR and NOTIFY were
defined, there was little consideration given to security and privacy defined, there was little consideration given to security and privacy
issues. Since the original definition of AXFR, new opinions have issues. Since the original definition of AXFR, new opinions have
appeared on the access to an entire zone's contents. In this document, appeared on the access to an entire zone's contents. In this document,
the basic mechanisms will be discussed separately from the permission to the basic mechanisms will be discussed separately from the permission
use these mechanisms. to use these mechanisms.
1.4 Coverage 1.4 Coverage
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. This is not strictly a clarification of the definition in documents. This is not strictly a clarification of the definition in
RFC 1034 and RFC 1035. This document will update those sections, and RFC 1034 and RFC 1035. This document will update those sections, and
invalidate at least one part of that definition. The goal of this invalidate at least one part of that definition. The goal of this
document is to define AXFR as it exists, or is supposed to exist, document is to define AXFR as it exists, or is supposed to exist,
currently. currently.
2 AXFR Messages 2 AXFR Messages
An AXFR message exchange (or session) consists of an AXFR query message An AXFR message exchange (or session) consists of an AXFR query message
and a set of AXFR response messages. In this document, AXFR client is and a set of AXFR response messages. In this document, AXFR client is
the sender of the AXFR query and the AXFR server is the responder. (Use the sender of the AXFR query and the AXFR server is the responder.
of terms such as master, slave, primary, secondary are not important to (Use of terms such as master, slave, primary, secondary are not
defining the AXFR exchange.) The reason for the imbalance in number of important to defining the AXFR exchange.) The reason for the imbalance
messages derives from large zones whose contents cannot be fit into the in number of messages derives from large zones whose contents cannot be
limited permissible size of a DNS message. 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 certain restricted to TCP [RFC0793]. The design of the AXFR process has
inherit features that are not easily ported to UDP [RFC0768]. certain inherit features that are not easily ported to UDP [RFC0768].
Nonetheless, AXFR over UDP has some potential use cases. AXFR over UDP
is not defined here and might some day appear in an extension document.
The basic format of an AXFR message is the DNS message as defined in RFC The basic format of an AXFR message is the DNS message as defined in
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" [RFC2929]
- "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]
- "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 is defined in The upper limit on the permissible size of a DNS message over TCP is
RFC 1035, section 2.3.4, and supplemented in RFC 2671, section 4.5. defined in RFC 1035, section 4.2.2. Unlike DNS messages over UDP,
The limit on the permissible size of a DNS message will be referenced this limit is not changed by EDNS0.
a few times in this document.
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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Z See note 2.1.1.c Z See note 2.1.1.c
AD See note 2.1.1.b AD See note 2.1.1.b
CD See note 2.1.1.b CD See note 2.1.1.b
RCODE MUST be 0 (No error) RCODE MUST be 0 (No error)
QDCOUNT MUST be 1 QDCOUNT MUST be 1
ANCOUNT MUST be 0 ANCOUNT MUST be 0
NSCOUNT MUST be 0 NSCOUNT MUST be 0
ARCOUNT See note 2.1.1.d ARCOUNT See note 2.1.1.d
Note 2.1.1.a Set to any value that the client desires. There Note 2.1.1.a Set to any value that the client desires. There
is no specific means for selecting the value in this field. However, is no specific means for selecting the value in this field.
consideration can be given to making it harder for forged messages to be (Recall that AXFR is done only via TCP connections.)
accepted by referencing the work in progress "Measures for making DNS
more resilient against forged answers" [FORGERY].
Note 2.1.1.b The value in this field has no meaning in the context of Note 2.1.1.b The value in this field has no meaning in the context of
AXFR query messages. For the client, it is RECOMMENDED that the AXFR query messages. For the client, it is RECOMMENDED that the
value be zero. For the server, it is RECOMMENDED ignoring this value. value be zero. The server MUST ignore this value.
Note 2.1.1.c The client MUST set to 0, the server MUST ignore. Note 2.1.1.c The client MUST set to 0, the server MUST ignore.
Note 2.1.1.d The value MAY be 0, 1 or 2. If it is 2, the additional Note 2.1.1.d The value MAY be 0, 1 or 2. If it is 2, the additional
section MUST contain both an EDNS0 [RFC2671] OPT resource record and section MUST contain both an EDNS0 [RFC2671] OPT resource record and
a record carrying transaction integrity and authentication data, a record carrying transaction integrity and authentication data,
currently a choice of TSIG [RFC2845] and SIG(0) [RFC2931]. If the currently a choice of TSIG [RFC2845] and SIG(0) [RFC2931]. If the
value is 1, then the additional section MUST contain either only an value is 1, then the additional section MUST contain either only an
EDNS0 OPT resource record or a record carrying transaction integrity EDNS0 OPT resource record or a record carrying transaction integrity
and authentication data. If the value is 0, the additional section and authentication data. If the value is 0, the additional section
MUST be empty. MUST be empty.
A note on "future proofing" this document. It is possible that in the
future more records might be introduced that share the property of
being placed in the additional section. Such records might be other
options to, say, TSIG and SIG(0) for message authentication or may
be completely unrelated to that service. In any case, each new record
that might appear in the additional section might expand the range of
values that this field can take on. As predicting the future is still
an unproven field, further details are not available. Check back
later for updates.
2.1.2 Query Section 2.1.2 Query Section
The Query section of the AXFR query MUST conform to section 4.1.2 of RFC The Query section of the AXFR query MUST conform to section 4.1.2 of
1035, and contain the following values: RFC 1035, and contain the following values:
QNAME the name of the zone requested QNAME the name of the zone requested
QTYPE AXFR [DNSVALS], see the registry for the numeric value QTYPE AXFR(= 252), the pseudo-RR type for zone transfer [DNSVALS]
QCLASS the class of the zone requested QCLASS the class of the zone requested
2.1.3 Answer Section 2.1.3 Answer Section
MUST be empty. MUST be empty.
2.1.4 Authority Section 2.1.4 Authority Section
MUST be empty. MUST be empty.
2.1.5 Additional Section 2.1.5 Additional Section
The client MAY include an EDNS0 OPT resource record. If the server The client MAY include an EDNS0 OPT resource record. If the server
has indicated that it does not support EDNS0, the client MUST send has indicated that it does not support EDNS0, the client MUST send
this section without an EDNS0 OPT resource record if there is a retry. this section without an EDNS0 OPT resource record if there is a retry.
Indication that a server does not support EDNS0 is not an explicit
element in the protocol, it is up to the client to interpret. Most
likely, the server will return a FORMERR which might be related to
the OPT resource record.
The client MAY include a transaction integrity and authentication The client MAY include a transaction integrity and authentication
resource record, currently a choice of TSIG or SIG(0). If the server resource record, currently a choice of TSIG or SIG(0). If the server
has indicated that it does not recognize the resource record, the client has indicated that it does not recognize the resource record, and
MUST send this section without such a resource record if there is a that the error is indeed caused by the resource record, the client
retry. probably ought not try again. Removing the security data in the
face of an obstacle ought to only be done with full awareness of the
implication of doing so.
If the client is aware that the server does not support EDNS0, it is
RECOMMENDED that this section be sent without the OPT resource record.
If the client is aware that the server will not participate in TSIG or
SIG(0), it is RECOMMENDED that the client not try to send such a record.
In general, if an AXFR client is aware that an AXFR server does not In general, if an AXFR client is aware that an AXFR server does not
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. A client MAY become aware of a server's the server using the mechanism (or at all). A client MAY become aware
abilities via a configuration setting. of a server's abilities via a configuration setting.
2.2 AXFR response 2.2 AXFR response
The AXFR response will consist of 0 or more messages. The AXFR response will consist of 0 or more messages.
A 0 message response is very exceptional. It is unhealthy for there
to be 0 responses in a protocol that is designed around a query -
response paradigm. 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 abuse. Therefore any earnest query has the expectation
of some response.
An AXFR response that is transferring the zone's contents will consist An AXFR response that is transferring the zone's contents will consist
of a series of DNS messages bounded in size by the limited permissible of a series of DNS messages bounded in size by the limited permissible
size. In such a series, the first message MUST begin with the SOA size. In such a series, the first message MUST begin with the SOA
resource record of the zone, the last message MUST conclude with the resource record of the zone, the last message MUST conclude with the
same SOA resource record. Intermediate message MUST NOT contain the same SOA resource record. Intermediate message MUST NOT contain the
SOA resource record. The first message MUST copy the Query Section SOA resource record. The first message MUST copy the Query Section
from the corresponding AXFR query message in to the first response from the corresponding AXFR query message in to the first response
message's query section. Subsequent messages MAY do the same. message's query section. Subsequent messages MAY do the same.
Editorial note "MAY" or SHOULD/are RECOMMENDED TO
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. Such a message MUST copy the AXFR query condition encountered - once the error condition is detected. Such
Query Section into its Query Section. a message MUST copy the AXFR query Query Section into its Query
Section.
An AXFR client MUST be able to react to no AXFR response Messages from An AXFR client might receive a number of AXFR response messages
free of an error condition before the message indicating the error
is received. But once an error is reported, the AXFR client can
assume this the reporting message is the last.
An AXFR client MUST be able to react to no AXFR response messages from
the server. An AXFR server MAY elect to silently discard the AXFR the server. An AXFR server MAY elect to silently discard the AXFR
query but this is only RECOMMENDED if the server has reasons to deduce query but this is only RECOMMENDED if the server has reasons to deduce
that the query was sent maliciously. that the query was sent maliciously.
An AXFR server MAY elect to close the underlying TCP connection in An AXFR server MAY elect to close the underlying TCP connection in
response to an AXFR query. Because this action could impact other response to an AXFR query. Because this action could impact other
DNS queries and responses, it is RECOMMENDED that this tactic only be DNS queries and responses, it is RECOMMENDED that this tactic only be
employed when there are strong indications of malicious activity. employed when there are strong indications of malicious activity.
Still, an AXFR client MUST be able to adequately react to this Still, an AXFR client MUST be able to adequately react to this
situation. situation.
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field to the query's ID, the client is NOT RECOMMENDED to issue any field to the query's ID, the client is NOT RECOMMENDED to issue any
other queries until the end of the zone transfer. A client MAY become other queries until the end of the zone transfer. A client MAY become
aware of a server's abilities via a configuration setting. aware of a server's abilities via a configuration setting.
Note 2.2.1.b If the RCODE is 0 (no error), then the AA bit MUST be 1. Note 2.2.1.b If the RCODE is 0 (no error), then the AA bit MUST be 1.
For any other value of RCODE, the AA bit MUST be set according to rules For any other value of RCODE, the AA bit MUST be set according to rules
for that error code. If in doubt, it is RECOMMENDED that is be set for that error code. If in doubt, it is RECOMMENDED that is be set
to 1. It is RECOMMENDED that the value be ignored by the AXFR client. to 1. It is RECOMMENDED that the value be ignored by the AXFR client.
Note 2.2.1.c It is RECOMMENDED that the server set the value to 0, Note 2.2.1.c It is RECOMMENDED that the server set the value to 0,
it is RECOMMENDED that the client ignore this value. the client MUST ignore this value.
The server MAY set this value according to the local policy regarding The server MAY set this value according to the local policy regarding
recursive service, but doing so might confuse the interpretation of the recursive service, but doing so might confuse the interpretation of the
response as AXFR can not be retrieved recursively. A client MAY note response as AXFR can not be retrieved recursively. A client MAY note
the server's policy regarding recursive from this value, but SHOULD NOT the server's policy regarding recursive from this value, but SHOULD NOT
conclude that the AXFR response was obtained recursively even if the RD conclude that the AXFR response was obtained recursively even if the RD
bit was 1 in the query. bit was 1 in the query.
Note 2.2.1.d The server MUST set to 0, and the client MUST ignore. Note 2.2.1.d The server MUST set to 0, and the client MUST ignore.
Note 2.2.1.e If the implementation supports the DNS Security Extensions Note 2.2.1.e If the implementation supports the DNS Security Extensions
(see below) then this value MUST be set according to the rules in RFC (see below) then this value MUST be set according to the rules in RFC
4035, section 3.1.6, "The AD and CD Bits in an Authoritative Response". 4035, section 3.1.6, "The AD and CD Bits in an Authoritative Response".
If the implementation does not support the DNS Security Extensions, then If the implementation does not support the DNS Security Extensions,
this value MUST be set to 0 and MUST be ignored upon receipt. then this value MUST be set to 0 and MUST be ignored upon receipt.
The DNS Security Extensions (DNSSEC) is defined in these base documents: The DNS Security Extensions (DNSSEC) is defined in these base
documents:
- "DNS Security Introduction and Requirements" [RFC4033] - "DNS Security Introduction and Requirements" [RFC4033]
- "Resource Records for the DNS Security Extensions" [RFC4034] - "Resource Records for the DNS Security Extensions" [RFC4034]
- "Protocol Modifications for the DNS Security Extensions" [RFC4035] - "Protocol Modifications for the DNS Security Extensions" [RFC4035]
Note 2.2.1.f In the absence of an error, the server MUST set the value Note 2.2.1.f In the absence of an error, the server MUST set the value
of this field to NoError. If a server is not authoritative for the of this field to NoError. If a server is not authoritative for the
queried zone, the server SHOULD set the value to NotAuth. (Reminder, queried zone, the server SHOULD set the value to NotAuth. (Reminder,
consult the appropriate IANA registry [DNSVALS].) If a client consult the appropriate IANA registry [DNSVALS].) If a client
receives any other value in response, it MUST act according to the receives any other value in response, it MUST act according to the
error. For example, a malformed AXFR query or the presence of an EDNS0 error. For example, a malformed AXFR query or the presence of an EDNS0
OPT resource record sent to an old server will garner a FormErr value. OPT resource record sent to an old server will garner a FormErr value.
This value is not set as part of the AXFR response processing. The same This value is not set as part of the AXFR response processing. The
is true for other error-indicating values. same is true for other error-indicating values.
Note 2.2.1.g The count of answer records MUST equal the number of Note 2.2.1.g The count of answer records MUST equal the number of
resource records in the AXFR Answer Section. When a server is aware resource records in the AXFR Answer Section. When a server is aware
that a client will only accept one resource record per response message, that a client will only accept one resource record per response
then the value MUST be 1. A server MAY be made aware of a client's message, then the value MUST be 1. A server MAY be made aware of a
limitations via configuration data. client's limitations via configuration data.
Note 2.2.1.h The value MAY be 0, 1 or 2. If it is 2, the additional Note 2.2.1.h The value MAY be 0, 1 or 2. If it is 2, the additional
section MUST contain both an EDNS0 [RFC2671] OPT resource record and section MUST contain both an EDNS0 [RFC2671] OPT resource record and
a record carrying transaction integrity and authentication data, a record carrying transaction integrity and authentication data,
currently a choice of TSIG [RFC2845] and SIG(0) [RFC2931]. If the currently a choice of TSIG [RFC2845] and SIG(0) [RFC2931]. If the
value is 1, then the additional section MUST contain either only an value is 1, then the additional section MUST contain either only an
EDNS0 OPT resource record or a record carrying transaction integrity EDNS0 OPT resource record or a record carrying transaction integrity
and authentication data. If the value is 0, the additional section and authentication data. If the value is 0, the additional section
MUST be empty. MUST be empty.
A note on "future proofing" this document. It is possible that in the
future more records might be introduced that share the property of
being placed in the additional section. Such records might be other
options to, say, TSIG and SIG(0), for message authentication or may
be completely unrelated to that service. In any case, each new record
that might appear in the additional section might expand the range of
values that this field can take on. As predicting the future is still
an unproven field, further details are not available. Check back
later for updates.
2.2.2 Query Section 2.2.2 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, 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.
2.2.3 Answer Section 2.2.3 Answer Section
MUST be populated with the zone contents. See later section on encoding MUST be populated with the zone contents. See later section on
zone contents. encoding zone contents.
2.2.4 Authority Section 2.2.4 Authority Section
MUST be empty. MUST be empty.
2.2.5 Additional Section 2.2.5 Additional Section
The contents of this section MUST follow the guidelines for EDNS0, TSIG, The contents of this section MUST follow the guidelines for EDNS0,
SIG(0), or what ever other future record is possible here. See the TSIG, SIG(0), or what ever other future record is possible here. See
appropriate specifications for instructions and restrictions. the appropriate specifications for instructions and restrictions.
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
In the answer section of AXFR response messages the resource records In the answer section of AXFR response messages the resource records
within a zone for the given serial number MUST appear. The definition within a zone for the given serial number MUST appear. The definition
of what belongs in a zone is described in RFC 1034, Section 4.2, "How of what belongs in a zone is described in RFC 1034, Section 4.2, "How
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".
The first resource record of the first AXFR response message sent by the The first resource record of the first AXFR response message sent by
AXFR server MUST be the zone's SOA resource record. The last resource the AXFR server MUST be the zone's SOA resource record. The last
record of the final AXFR response message sent by the AXFR server MUST resource record of the final AXFR response message sent by the AXFR
be the zone's SOA resource record. The order and grouping of all other server MUST be the zone's SOA resource record. The order and grouping
records in the AXFR is arbitrary, but the AXFR server SHOULD group of all other records in the AXFR is arbitrary, but the AXFR server
resource record sets together. SHOULD group resource record sets together.
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 records populate an AXFR response message with as many complete resource
as will fit within the limited permissible message size. records as will fit within the limited permissible message size.
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.
3.2 Delegation Records 3.2 Delegation Records
In RFC 1034, section 4.2.1, this text appears (keep in mind that the use In RFC 1034, section 4.2.1, this text appears (keep in mind that the
of the word "should" in the quotation is exempt from the interpretation "should" in the quotation predates [BCP14], cf. section 1.1) "The RRs
in section 1.1) "The RRs that describe cuts ... should be exactly the that describe cuts ... should be exactly the same as the corresponding
same as the corresponding RRs in the top node of the subzone." There RRs in the top node of the subzone." There has been some controversy
has been some controversy over this statement and the impact on which over this statement and the impact on which NS resource records are
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 a slew of DNSSEC resource
records. There are also some DNSSEC resource record sets that are records. There are also some DNSSEC resource record sets that are
explicitly different between the cut point and the apex. The explicitly different between the cut point and the apex. The
discussion here is restricted to just the NS resource record set and discussion here is restricted to just the NS resource record set and
glue as these "describe cuts." 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 there being protocol is robust enough to overcome inconsistencies up to (but not
no parent indicated NS resource record referencing a server that is able including) there being no parent indicated NS resource record
to serve the child zone. This robustness is one quality that has referencing a server that is able to serve the child zone. This
fueled the success of the DNS. Still, the inconsistency is a error robustness is one quality that has fueled the success of the DNS.
state and steps need to be taken to make it apparent (if it is Still, the inconsistency is a error state and steps need to be taken
unplanned) and to make it clear once the inconsistency has been removed. to make it apparent (if it is unplanned) and to make it clear once
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 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 or registered with the zone whether it agrees with the authoritative set
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:
1) The AXFR server might not be able to determine that there is an 1) The AXFR server might not be able to determine that there is an
inconsistency given local data, hence requiring consistency would mean inconsistency given local data, hence requiring consistency would mean
a lot more needed work and even network retrieval of data. An a lot more needed work and even network retrieval of data. An
authoritative server ought not be required to perform any queries. authoritative server ought not be required to perform any queries.
2) By transferring the inconsistent NS resource records from a server 2) By transferring the inconsistent NS resource records from a server
that is authoritative for both the cut point and the apex to a client that is authoritative for both the cut point and the apex to a client
that is not authoritative for both, the error is exposed. For example, that is not authoritative for both, the error is exposed. For example,
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 in a 3) The inconsistent NS resource record set might indicate a problem
registration database. in a registration database.
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
requests and recieves an IXFR transfer from one server followed by
another IXFR transfer from the other server, the client can encounter
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
exist.
(Editorial note, the 4th reason was suggested, but I don't see how
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, RFC 1034, section 4.2.1, 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.
skipping to change at line 518 skipping to change at line 564
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
comment made in RFC 1034, section 3.1, "Name space specifications and comment made in RFC 1034, section 3.1, "Name space specifications and
terminology" which says "When you receive a domain name or label, you terminology" which says "When you receive a domain name or label, you
should preserve its case." ("Should" in the quote predates [BCP14].) should preserve its case." ("Should" in the quote predates [BCP14].)
Name compression in an AXFR message MUST preserve the case of the Name compression in an AXFR message MUST preserve the case of the
original domain name. That is, although when comparing a domain name, original domain name. That is, although when comparing a domain name,
"a" equals "A", when comparing for the purposes of message comparison, "a" equals "A", when comparing for the purposes of message compression,
"a" is not equal to "A". "a" is not equal to "A". Note that this is not the usual definition
of name comparison in the DNS protocol and represents a new
requirement on AXFR servers.
Name compression of RDATA in an AXFR message MAY only be done on Rules governing name compression of RDATA in an AXFR message MUST
resource record types which explicitly permit such compression. abide by the specification in "Handling of Unknown DNS Resource Record
(RR) Types" [RFC3597], specifically, section 4 on "Domain Name
Compression."
3.5 Occluded Names
Dynamic Update [RFC2136] (and including DNAME [2672]) operations can
have a side effect of occluding names in a zone. 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 for to
the look up process. The addition of a DNAME resource record set has
the same impact. The subordinate names are said to be "occluded."
Occluded names MUST be included in AXFR responses. An AXFR client MUST
be able to identify and handle occluded names. The rationale for this
action is based on a speedy recovery if the dynamic update operation
was in error and is to be undone.
4 Transport 4 Transport
AXFR sessions are restricted by RFC 1034, section 4.3.5's "because AXFR sessions are currently restricted to TCP by section 4.3.5 of RFC
accuracy is essential, TCP or some other reliable protocol must be used 1034 that states: "Because accuracy is essential, TCP or some other
for AXFR requests." The most common scenario is for an AXFR client reliable protocol must be used for AXFR requests." The most common
to open a TCP connection to the AXFR server, send an AXFR query, scenario is for an AXFR client to open a TCP connection to the AXFR
receive the AXFR response, and then close the connection. There are server, send an AXFR query, receive the AXFR response, and then
variations on this, such as a query for the zone's SOA resource close the connection. There are variations on this, such as a query
record first, and so on. for the zone's SOA resource record first, and so on.
Two issues have emerged since the original specification of AXFR. Two issues have emerged since the original specification of AXFR.
One is that lack of specificity has yielded some implementations One is that lack of specificity has yielded some implementations
that assume the TCP connection is dedicated to the single AXFR that assume the TCP connection is dedicated to the single AXFR
session, which has led to implementation choices that prevent either session, which has led to implementation choices that prevent either
multiple concurrent zone transfers or the use of the open connection multiple concurrent zone transfers or the use of the open connection
for other queries. The other issue is the prospect of using UDP as a 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 transport has come to look promising because of trends in the past
two decades. two decades.
skipping to change at line 584 skipping to change at line 648
the AXFR exchange as well as guidelines on interactions with older the AXFR exchange as well as guidelines on interactions with older
software. Better performance includes being able to multiplex DNS software. Better performance includes being able to multiplex DNS
message exchanges including zone transfer sessions. Guidelines for message exchanges including zone transfer sessions. Guidelines for
interacting with older software are generally applicable to AXFR interacting with older software are generally applicable to AXFR
clients as reversing the situation, older AXFR client and newer clients as reversing the situation, older AXFR client and newer
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 upon any An AXFR client MAY request an connection to an AXFR server for any
demand. 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. This no apparent need to use the connection for some time period. The
latter comment is made so that the AXFR server does not have AXFR server ought not to maintain idle connections, the burden of
to keep open idle connections, and placing the planning for a connection closure ought to be on the client. Apparent need for
connection closure on the client. Apparent need for the connection the connection is a judgement for the AXFR client and the DNS
is a judgement for the AXFR client and the DNS client in general, if client. If the connection is used for multiple sessions, or it is
the connection is used for multiple sessions, or it is know sessions known sessions will be coming or is there is other query/response
will be coming, or is there is other query/response traffic on the traffic on the open connection, that is "apparent need."
open connection, that 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,
attempting to restart the connection would be proper. If the attempting to restart the connection would be proper. If the
disruption was caused by a medium or long term disruption, the AXFR disruption was caused by a medium or long term disruption, the AXFR
client would be wise to not spend too many resources trying to rebuild client would be wise to not spend too many resources trying to rebuild
the connection. Finally, if the connection was dropped because of a the connection. Finally, if the connection was dropped because of a
policy at the AXFR server (as can be the case with older AXFR servers), policy at the AXFR server (as can be the case with older AXFR servers),
the AXFR client would be wise not retry the connection. Unfortunately, the AXFR client would be wise to not retry the connection.
knowing which of the three cases above applies is not clear Unfortunately, knowing which of the three cases above applies is not
(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 that 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 protocol). updated (which is of course, not an event captured in the DNS
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
all AXFR sessions in place. No retry activity is necessary, that is all AXFR sessions in place. No retry activity is necessary, that is
initiated by the AXFR client. initiated by the AXFR client.
skipping to change at line 660 skipping to change at line 724
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. By default, a DNS implementation SHOULD only allow
the designated authoritative servers to have access to the zone. the designated authoritative servers to have access to the zone.
An implementation SHOULD allow access to be granted to Internet Protocol An implementation SHOULD allow access to be granted to Internet
addresses and ranges, regardless of whether a source address could be Protocol addresses and ranges, regardless of whether a source address
spoofed. Combining this with techniques such as Virtual Private could be spoofed. Combining this with techniques such as Virtual
Networks (VPN) [RFC2764] or Virtual LANs has proven to be effective. Private Networks (VPN) [RFC2764] or Virtual LANs has proven to be
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."
6 Zone Integrity 6 Zone Integrity
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 or opportunity, protection can be afforded via dedicated links, physical
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 Backwards Compatibility
Describing backwards compatibility is difficult because of a 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 implementers desire to maintain interoperability. depending on the implementer's desire to maintain interoperability.
It is unfortunate that needs to fall back to older behavior cannot be It is unfortunate that a need to fall back to older behavior cannot be
discovered, hence need 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 7.1 Server
An AXFR server has the luxury of being able to react to an AXFR client's An AXFR server has the luxury of being able to react to an AXFR
abilities with the exception of knowing if the client can accept client's abilities with the exception of knowing if the client can
multiple resource records per AXFR response message. The knowledge that accept multiple resource records per AXFR response message. The
a client is so restricted apparently cannot be discovered, hence it has knowledge that a client is so restricted apparently cannot be
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 7.2 Client
An AXFR client has the opportunity to try extensions when querying an An AXFR client has the opportunity to try extensions when querying
AXFR server. an AXFR server.
The use of EDNS0 to increase the DNS message size, offer authorizing
proof, or to invoke message integrity can be tried and rejected by the
AXFR server via the methods already described as part of the EDNS0
mechanism.
If an AXFR client attempts to use the UDP transport, non-response from
the AXFR server or other error message can indicate not to retry that.
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 and AXFR session SHOULD be aborted if it interrupts the original request
SHOULD take into consideration whether the AXFR server intends to close and SHOULD take into consideration whether the AXFR server intends to
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 8 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 9 IANA Considerations
skipping to change at line 771 skipping to change at line 828
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, ... Calder, Tony Finch, Ian Jackson, Andreas Gustafsson, Brian Wellington,
...
12 References 12 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,
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. Additionally, these documents can be obtained via the IETF web site.
12.1 Normative 12.1 Normative
[RFC0793] "Transmission Control Protocol." J. Postel. September 1981. [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
[RFC0768] "User Datagram Protocol. " J. Postel. August 1980. September 1981.
[RFC1034] "Domain names - concepts and facilities.", P.V. Mockapetris. [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August
Nov-01-1987. 1980.
[RFC1035] "Domain names - implementation and specification." P.V. [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
Mockapetris. Nov-01-1987. STD 13, RFC 1034, November 1987.
[RFC1995] "Incremental Zone Transfer in DNS." M. Ohta. August 1996. [RFC1035] Mockapetris, P., "Domain names - implementation and
[RFC1996] "A Mechanism for Prompt Notification of Zone Changes (DNS specification", STD 13, RFC 1035, November 1987.
NOTIFY)." P. Vixie. August 1996. [RFC1995] Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,
[RFC2136] "Dynamic Updates in the Domain Name System (DNS UPDATE)." August 1996.
P. Vixie, Ed., S. Thomson, Y. Rekhter, J. Bound. April 1997. [RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone
[RFC2671] "Extension Mechanisms for DNS (EDNS0)." P. Vixie. Changes (DNS NOTIFY)", RFC 1996, August 1996.
[RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC
2136, April 1997.
[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC 2671,
August 1999. August 1999.
[RFC2845] "Secret Key Transaction Authentication for DNS (TSIG)." [RFC2672] Crawford, M., "Non-Terminal DNS Name Redirection", RFC 2672,
P. Vixie, O. Gudmundsson, D. Eastlake, B. Wellington. August 1999.
May 2000. [RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
[RFC2929] "Domain Name System (DNS) IANA Considerations." D. Eastlake Wellington, "Secret Key Transaction Authentication for DNS
3rd, E. Brunner-Williams, B. Manning. September 2000. (TSIG)", RFC 2845, May 2000.
[RFC2930] "Secret Key Establishment for DNS (TKEY RR)." D. Eastlake. [RFC2929] Eastlake 3rd, D., Brunner-Williams, E., and B. Manning,
September 2000. "Domain Name System (DNS) IANA Considerations", BCP 42, RFC
[RFC2931] "DNS Request and Transaction Signatures ( SIG(0)s)." 2929, September 2000.
D. Eastlake. September 2000. [RFC2930] Eastlake 3rd, D., "Secret Key Establishment for DNS (TKEY
[RFC3425] "Obsoleting IQUERY." D. Lawrence. November 2002. RR)", RFC 2930, September 2000.
[RFC4033] "DNS Security Introduction and Requirements." [RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures
R. Arends, R. Austein, M. Larson, D. Massey, S. Rose. March ( SIG(0)s )", RFC 2931, September 2000.
2005. [RFC3425] Lawrence, D., "Obsoleting IQUERY", RFC 3425, November 2002.
[RFC4034] "Resource Records for the DNS Security Extensions." [RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record
R. Arends, R. Austein, M. Larson, D. Massey, S. Rose. March (RR) Types", RFC 3597, September 2003.
2005. [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
[RFC4035] "Protocol Modifications for the DNS Security Extensions." Rose, "DNS Security Introduction and Requirements", RFC 4033,
R. Arends, R. Austein, M. Larson, D. Massey, S. Rose. March March 2005.
2005. [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
[RFC4635] "HMAC SHA (Hashed Message Authentication Code, Secure Hash Rose, "Resource Records for the DNS Security Extensions",
Algorithm) TSIG Algorithm Identifiers." D. Eastlake 3rd. RFC 4034, March 2005.
August 2006. [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, March 2005.
[RFC4635] Eastlake 3rd, D., "HMAC SHA (Hashed Message Authentication
Code, Secure Hash Algorithm) TSIG Algorithm Identifiers",
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 12.2 Informative
[BCP14] "Key words for use in RFCs to Indicate Requirement Levels." [BCP14] Bradner, S., "Key words for use in RFCs to Indicate
S. Bradner. March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2764] "A Framework for IP Based Virtual Private Networks." B. [RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A.
Gleeson, A. Lin, J. Heinanen, G. Armitage, A. Malis. Malis, "A Framework for IP Based Virtual Private Networks",
February 2000. RFC 2764, February 2000.
[RFC3490] "Internationalizing Domain Names in Applications (IDNA)." P. [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
Faltstrom, P. Hoffman, A. Costello. March 2003. "Internationalizing Domain Names in Applications (IDNA)", RFC
[FORGERY] "Measures for making DNS more resilient against forged 3490, March 2003.
answers." A. Hubert, R. van Mook. Work in Progress.
http://www.ietf.org/internet-drafts/
draft-ietf-dnsext-forgery-resilience-01.txt
13 Editor's Address 13 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 Full Copyright Statement
 End of changes. 60 change blocks. 
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