DNSIND Working Group K. Dunlap
INTERNET-DRAFT Check Point Software
<draft-dunlap-dns-duxfr-00.txt> P. Vixie
ISC
September 1999
Dynamic Update Zone Transfer
Copyright (C) The Internet Society (1999). All Rights Reserved.
Status of This Memo
This draft, file name draft-dunlap-dns-duxfr-00.txt, is intended to
become a Proposed Standard RFC. Distribution of this document is unlim-
ited. Comments should be sent to <namedroppers@internic.net> or to the
authors.
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026. Internet-Drafts are working docu-
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Abstract
This document proposes an alternative extension to the DNS protocol for
Incremental zone transfer (IXFR) [RFC1995]. This extension uses the
mechanisms for adding and deleting Resource Records specified in
[RFC2136] to transmit the changes between authoritative servers of a
zone.
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1 - Introduction
For rapid propagation of changes to a DNS database [STD13], it is neces-
sary to reduce latency by actively notifying servers of the change.
This is accomplished by the DNS NOTIFY Mechanism [RFC1996].
The simple method described for Incremental transfer (IXFR), in
[RFC1995], does not adequately address the complexity of the problem.
Dynamic Update Zone Transfer (DUXFR), as proposed, is a mechanism to
transmit the complexity of changes in the zone and still have the effi-
ciency of IXFR means to propagate changed portions of a zone.
In this document, a slave name server which requests DUXFR is called a
DUXFR client and a master or slave name server which responds to the
request is called a DUXFR server.
2 - Brief Description of the Protocol
If a DUXFR client, which likely has an older version of a zone, thinks
it needs a newer version of the zone (typically through SOA refresh
timeout or the NOTIFY mechanism), it sends a DUXFR message containing
the SOA serial number of its (presumably outdated) copy of the zone.
A DUXFR server should keep record of the newest version of the zone and
the differences between that copy and several older versions. When a
DUXFR request with an older version number is received, the DUXFR server
needs to send only the differences required to make that version
current. These differences are sent using the DNS UPDATE format packets
for deletes and add specified in [RFC2136 2.5].
When a zone has been updated, it should be saved in stable storage
before the new version is used to respond to DUXFR (or AXFR) queries.
Otherwise, if the server crashes, data which is no longer available may
have been distributed to slave servers, which can cause persistent data-
base inconsistencies.
If a DUXFR query with the same or newer version number than that of the
server is received, it is replied to with a single SOA record of the
server's current version, just as in IXFR.
The Transport protocol for DUXFR queries is TCP/IP.
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3 - Query Format
The DUXFR Query format is based on the standard DNS UPDATE Message For-
mat. In the DNS Packet Header the Opcode is set to UPDATE and the Zone
Type (ZTYPE) being set to AXFR. The Additional section containing the
SOA record of the client's version of the zone.
4 - Response Format
The response packets to the DUXFR query are in the standard DNS UPDATE
Message Format. The records in the Update Section are formatted using
the four sets of semantics for adding and deleting Resource Records
specified in the ``Update Section'' in [RFC2136 2.5]. The client will
process these changes using the prerequisite for the transaction as the
existence of the SOA serial number specified in the Additional section
of the DUXFR query.
The response to a DUXFR query, when the server no longer has all the
previous history from the version the client requests, will be a
Response code (RCODE) of "Refused". It is recommended that the client
retry with an AXFR query described in [RFC1034 4.3.5].
It is recommended that the Prerequisite sections of the DNS message be
empty on transmission and ignored on reception. The Additional section
may contain necessary data such as signatures as specified by other
extensions to [RFC 2136].
5 - Version Overhead
A DUXFR server can not be required to hold all previous versions forever
and may delete them anytime. In general, there is a trade-off between
the size of storage space and the possibility of using DUXFR.
Information about older versions should be purged if the total length of
a DUXFR response would be longer than that of an AXFR response. Given
that the purpose of DUXFR is to reduce AXFR overhead, this strategy is
quite reasonable. The strategy assures that the amount of storage
required is at most twice that of the current zone information.
Information older than the SOA expire period may also be purged.
6 - IANA Considerations
No IANA services are required by this document.
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7 - Security Considerations
DNS is related to several security problems, no attempt is made to fix
them in this document.
The authors believe that this document does not introduce any additional
security problems to the current DNS protocol.
8 - Examples
Given the following three generations of data with the current serial
number of 3.
(
1 600 600 3600000 604800 )
IN NS NS.Example.Com.
NS.Example.Com. IN A 192.168.1.5
Vangogh.Example.Com. IN A 192.168.1.21
Vangogh.Example.Com. is removed and Monet.Example.Com. is added.
2 600 600 3600000 604800 )
IN NS NS.Example.Com.
NS.Example.Com. IN A 192.168.1.5
Monet.Example.Com. IN A 192.168.6.27
IN A 192.168.3.128
One of the IP address of Monet.Example.Com. is changed.
3 600 600 3600000 604800 )
IN NS NS.Example.Com.
NS.Example.Com. IN A 192.168.1.5
Monet.Example.Com. IN A 192.168.6.42
IN A 192.168.3.128
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The following DUXFR query:
+--------------------------------------------------+
Header | OPCODE=QUERY, QR=Request |
+--------------------------------------------------+
Zone | QNAME=Example.Com., QCLASS=IN, QTYPE=AXFR |
+--------------------------------------------------+
Prerequisite | <empty> |
+--------------------------------------------------+
Update | <empty> |
+--------------------------------------------------+
Additional | Example.Com. IN SOA serial=1 |
+--------------------------------------------------+
The reply could be with the following DUXFR response with Update packets
in the Answer Section:
+--------------------------------------------------+
Header | OPCODE=QUERY, QR=Response |
+--------------------------------------------------+
Zone | QNAME=Example.Com., QCLASS=IN, QTYPE=AXFR |
+--------------------------------------------------+
Prerequisite | Example.Com. IN SOA serial=1 |
+--------------------------------------------------+
Update | Vangogh.Example.Com. 0 ANY A 192.168.1.21 |
| Monet.Example.Com. IN A 192.168.6.42 |
| Monet.Example.Com. IN A 192.168.3.128 |
| Example.Com. 0 IN SOA serial=1 |
| Example.Com. IN SOA serial=2 |
| Monet.Example.Com. 0 ANY A 192.168.6.42 |
| Example.Com. 0 ANY SOA serial=2 |
| Example.Com. IN SOA serial=3 |
+--------------------------------------------------+
Additional | <empty> |
+--------------------------------------------------+
or with the following Compressed DUXFR response with Update packets in
the Answer Section:
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+--------------------------------------------------+
Header | OPCODE=QUERY, QR=Response |
+--------------------------------------------------+
Zone | QNAME=Example.Com., QCLASS=IN, QTYPE=AXFR |
+--------------------------------------------------+
Prerequisite | Example.Com. IN SOA serial=1 |
+--------------------------------------------------+
Update | Vangogh.Example.Com. 0 ANY A 192.168.1.21 |
| Monet.Example.Com. IN A 192.168.6.42 |
| Monet.Example.Com. IN A 192.168.3.128 |
| Example.Com. 0 ANY SOA serial=1 |
| Example.Com. IN SOA serial=3 |
+--------------------------------------------------+
Additional | <empty> |
+--------------------------------------------------+
References
[RFC1034]]
P. Mockapetris, ``Domain Names - Concepts and Facilities'' STD
13, RFC 1034, USC/Information Sciences Institute, November 1987.
[RFC1035]
P. Mockapetris, ``Domain Names - Implementation and Specifica-
tion'' RFC 1035, USC/Information Sciences Institute, November
1987.
[RFC1996]
P. Vixie, ``A Mechanism for Prompt Notification of Zone Changes
(DNS Notify)'' RFC 1996, August 1996
[RFC1995]
M. Ohta, ``Incremental Zone Transfer in DNS'' RFC 1995, August
1996.
[RFC2026]
S. Bradner, ``the Internet Standards Process -- Revision 3'' RFC
2026, Harvard University, October 1996.
[RFC2136]
P. Vixie, S. Thomson, Y. Rekhter and J. Bound, ``Dynamic
Updates in the Domain Name System (DNS UPDATE)'' RFC 2136,
April 1997
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Author's Address
Kevin J. Dunlap
Check Point Software Technologies, Inc.
The Meta IP Group
119 South Main Street, Suite 200
Seattle, WA 98033
+1 206 674 3700
<kevind@MetaIP.CheckPoint.Com>
Paul Vixie
Internet Software Consortium
950 Charter Street
Redwood City, CA 94063
+1 650 779 7001
<vixie@isc.org>
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