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DNSSEC Working Group                          Brian Wellington (TISLabs)
INTERNET-DRAFT                                             February 1999


Updates: RFC 2065, RFC 2136, [TSIG]
Replaces: RFC 2137, [update2]

         Simple Secure Domain Name System (DNS) Dynamic Update

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as ``work in progress.''

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at


   This draft proposes an alternative method for performing secure
   Domain Name System (DNS) dynamic updates.  The method described here
   is both simple and flexible enough to represent any policy decisions.
   Secure communication based on request/transaction signatures [TSIG]
   is used to provide authentication and authorization.

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1 - Introduction

Dynamic update operations for the Domain Name System are defined in
[RFC2136], but no mechanisms for security have been defined.  Request
and transaction signatures are defined in [TSIG].

Familiarity with the DNS system [RFC1034, RFC1035] as well as the
proposals mentioned above is assumed.  Familiarity with DNS Security
[RFC2065, secext2] is assumed in section (4).

1.1 - Overview of DNS Dynamic Update

DNS dynamic update defines a new DNS opcode and a new interpretation of
the DNS message if that opcode is used.  An update can specify
insertions or deletions of data, along with prerequisites necessary for
the updates to occur.  All tests and changes for a DNS update request
are restricted to a single zone, and are performed at the primary server
for the zone.  The primary server for a dynamic zone must increment the
zone SOA serial number when an update occurs or before the next
retrieval of the SOA.

1.2 - Overview of DNS Transaction Security

[TSIG] provides a means for two processes that share a secret key to
authenticate DNS requests and responses sent between them.  This is done
by appending TSIG digital signature (keyed hash) RRs to those messages.
Keyed hashes are simple to calculate and verify, and do not require
caching of data.

2 - Authentication

TSIG records are attached to all secure dynamic update messages.  This
allows the server to verifiably determine the originator of the message.
It can then use this information in the decision of whether to accept
the update.  DNSSEC SIG records may be included in an update message,
but MAY NOT be used for authentication purposes in the update protocol.
If a message fails the authentication test due to an unauthorized key,
the failure is indicated with the REFUSED rcode.  Other TSIG or dynamic
update errors are returned unchanged.

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3 - Policy

All policy is dictated by the server and is configurable by the zone
administrator.  The server's policy defines criteria which determine if
the key used to sign the update is permitted to update the records
requested.  By default, a key cannot make any changes to the zone; the
key's scope must be explicitly enabled.  There are several reasons that
this process is implemented in the server and not the protocol (as in
[RFC2137, update2], where the signatory bits of KEY records may define
the policy).

3.1 - Flexibility

Storing policy in the signatory fields of DNS keys is overly
restrictive.  Only a fixed number of bits are present, which means that
only a fixed number of policy decisions are representable.  There are
many decisions that do not fit into the framework imposed by the
signatory field; a zone administrator cannot effectively impose a policy
not implemented in the draft defining the field.

There may be any number of policies applied in the process of
authorization, and there are no restrictions on the scope of these
policies.  Implementation of the policies is beyond the scope of this

3.2 - Simplicity

Policy decisions in the server could be used as an adjunct to policy
fields in the KEY records.  This could lead to confusion if the policies
are inconsistent.  Furthermore, since there is no need to expose
policies, a central configuration point is more logical.

3.3 - Extendibility

If a policy is changed, there are no changes made to the DNS protocol or
the data on the wire.  This means that new policies can be defined at
any point without adverse effects or interoperability concerns.

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4 - Interaction with DNSSEC

A successful update request may or may not include SIG records for each
RRset.  Since SIG records are not used for authentication in this
protocol, they are not required.  If the updated zone is signed, the
server will generate SIG records for each incoming RRset with the Zone
key (which MUST be online).  If there are any non-DNSSEC SIG records
present, they are retained.  If there are SIG records that have been
generated by the appropriate zone KEY, these SIGs are verified and
retained if the verification is successful.  DNSSEC SIG records
generated by other KEYs are dropped.  The server will generate SIG
records for each set with the Zone key, unless one has already been
verified.  The server will also generate a new SOA record and possibly
new NXT records, and sign these with the Zone key.

The server MUST update the SOA record and MAY generate new NXT records
when an update is received.  Unlike traditional dynamic update, the
client is forbidden from updating SOA 1 NXT records.

5 - Security considerations

For a secure zone to support dynamic update, the Zone key MUST be online
(unlike [RFC2137]).  No additional protection is offered by having the
Zone key offline and an Update key online, since compromising any key
that can sign the zone's data compromises the zone itself.

6 - References

[RFC1034]  P. Mockapetris, ``Domain Names - Concepts and Facilities,''
           RFC 1034, ISI, November 1987.

[RFC1035]  P. Mockapetris, ``Domain Names - Implementation and
           Specification,'' RFC 1035, ISI, November 1987.

[RFC2065]  D. Eastlake, C. Kaufman, ``Domain Name System Security
           Extensions,'' RFC 2065, CyberCash & Iris, January 1997.

[RFC2136]  P. Vixie (Ed.), S. Thomson, Y. Rekhter, J. Bound ``Dynamic
           Updates in the Domain Name System,'' RFC 2136, ISC & Bellcore
           & Cisco & DEC, April 1997.

[RFC2137]  D. Eastlake ``Secure Domain Name System Dynamic Update,'' RFC
           2137, CyberCash, April 1997.

[secext2]  D. Eastlake ``Domain Name System Security Extensions,''
           draft-ietf-dnssec-secext2-07.txt, IBM, December 1998.

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[TSIG]     P. Vixie (ed), O. Gudmundsson, D. Eastlake, B. Wellington
           ``Secret Key Transaction Signatures for DNS (TSIG),'' draft-
           ietf-dnsind-tsig-08.txt, ISC & TISLabs & IBM & TISLabs,
           February 1999.

[update2]  D. Eastlake ``Secure Domain Name System (DNS) Dynamic
           Update,'' draft-ietf-dnssec-update2-00.txt, Transfinite
           Systems Company, August 1998.

7 - Author's Address

   Brian Wellington
       TISLabs at Network Associates
       3060 Washington Road, Route 97
       Glenwood, MD 21738
       +1 443 259 2369

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