Network Working Group M. StJohns
Internet-Draft Nominum, Inc.
Expires: December 12, 2003 June 13, 2003
Using DNSSEC-secured NOTIFY to Trigger Parent Zone Updating
draft-stjohns-secure-notify-00
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document describes an extension or revision to the DNS NOTIFY
mechanism which would allow a child zone to securely notify a parent
zone of the need to update records that appear in the parent zone,
but are related to records in the child zone. At this time, the two
resource record types are the NS or Name Server record, and the DS or
Delegation Signer record.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. General Mechanism . . . . . . . . . . . . . . . . . . . . . 4
2.1 Update Methods . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 Automatic Update . . . . . . . . . . . . . . . . . . . . . . 5
2.1.2 Manual Update . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.3 Parent Pull . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Update of Parent DS Records . . . . . . . . . . . . . . . . 6
2.3 Update of Parent NS Records . . . . . . . . . . . . . . . . 6
2.4 Uncommitted Updates . . . . . . . . . . . . . . . . . . . . 6
3. Parent Zone Secondary Server Update . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . 8
Normative References . . . . . . . . . . . . . . . . . . . . 7
A. Discussion: NOTIFY vs UPDATE & Push vs Pull . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . 9
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1. Introduction
Author's note: "SEP" will be changed to whatever the final version of
[SEPFLAG] ends up making it.
Author's note: There may be too many options at places in this
document. Prior to any submission for advancement to standard, the
intent is reduce each set of choices down to either a single
preferred approach, or a preferred choice plus one alternate.
The orignal DNS NOTIFY RFC [RFC1996] specified a mechanism for a
master server of a zone to tell its secondary servers that a zone had
changed. The secondary server could then initiate a transfer from
the master server to update its copy of that zone. RFC1996 only
specified a notify of a change of an SOA record, and only a
notification between primary and secondary servers.
The original DNS Security (DNSSEC) RFC [RFC2535] specified various
mechanisms for securing (i.e. authenticating) the data within the
DNS. It also included mechanisms for signing transactions. [DSREC]
specifies a change to RFC2535 which removes the glue KEY record from
a parent domain, and replaces it with the Delegation Signer or DS
record which points at a KEY record held by a child zone. The DS
record is only present in the parent zone at a delegation point.
This document specifies a mechanism for a child zone to notify a
parent zone (more specifically, the master server of a parent zone)
of changes in the child zone which might affect glue information held
in the parent. The transaction signature mechanisms specified in
RFC2535 and modified in RFC2931 [RFC2931] are used to provide
authentication of the notification. A notify is triggered by a
change to records in the child zone which have or should have related
records in the parent. At this time, these are either the KSK KEY
records (a subset of the KEY RRSet)which are represented in the
parent by DS records, or records in the child's apex NS RRSet. Once
notified, the parent MAY update its glue information.
Note that while both parent and child zones may have RRSets of SIG
and NXT with the same name, the content of those records in the
parent zone is directly related to the content of the parent zone,
and not to the child zone and vice versa.
Glue "A" records could be updated using this mechanism, but may be
problematic as not all "A" records covering the glue "NS" records
will always reside within the child zone. Specifically, not all names
contained in NS records for a zone will be names within the zone. In
fact, best practice requires that a zone be served by at least one
server that can be referenced by a name not within that zone.
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. General Mechanism
When the primary server of the child zone detects a change in either
its set of secure-entry-point (SEP) KEY records or in its set of NS
records, it MAY (configuration dependent) send a NOTIFY to the
primary (or other designated server) of its parent zone. The NOTIFY
includes the complete set of records which make up the changed RRSet.
If more than one type of RRSet has changed, seperate NOTIFYs should
be sent for each change, and per RFC1996, no more than one NOTIFY
should be outstanding at any time.
The NOTIFY is protected using a transaction signature SIG(0)RR
[RFC2931]. The private key used to form the signature MUST be one of
the ones currently used to sign the KEY RRSet in the child zone (e.g.
there MUST be a SIG(KEY) record pointing at that key). If the SEP
KEY record associated with this private key is not otherwise included
in the NOTIFY message, it SHOULD be included in the additional
information section of the NOTIFY message. If the KEY record is not
included, there will be a delay in completing the NOTIFY transaction
while the receiving parent server retrieves the KEY record from the
child.
If the SIG(0)is missing the server MUST return an error code of ??.
The receiving server first checks to see if it holds a DS record that
maps to the KEY associated with the SIG(0) on the NOTIFY. If the DS
exists AND is signed, the signature over the NOTIFY is validated
against the KEY record. If the DS does not exist, the server MUST
return an error code of ??
If the signature verifies, the NOTIFY message should be considered
authentic, and the server then sends the NOTIFY response. If the
signature does not verify, the server MUST return an error code of ??
The sending server should continue to retry until it gets some
response from the parent zone server, or until too many retries. See
RFC1996 for details on general retransmission and retry procedures
for NOTIFY. [Author's note: This may not be sufficient guidance to
cover the case where the parent has to retrieve the KEY record from
the child.]
If the policy at the receiving server permits, the data included in
the NOTIFY and secured under the signature MUST be considered
authentic, and MUST be used as the source data to update the records
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held by the parent zone. If policy does not permit acceptance of the
data in the NOTIFY, or if data is missing (e.g. if the TC bit is
set), the parent server MUST query the child zone to retrieve any
missing data (e.g. KEY records, NS records, applicable SIG records).
The retrieved data MUST be secured (e.g. the SIG records must verify,
and the KEY used to sign the SIG MUST have a signed DS present in the
parent zone.)
At this point, the parent server has enough information to update the
records it holds. How it does it is a matter of policy.
2.1 Update Methods
Author's note - I personally prefer Automatic or Manual - I think
Parent Pull is the wrong model here.
2.1.1 Automatic Update
In the "Automatic Update" model, the parent server has immediate
access to the private keys needed to sign the new records. Once the
NOTIFY is verified, and the contents of the new records are checked
or generated, the parent zone signs the new records and publishes
them.
2.1.2 Manual Update
In the "Manual Update" model, private keys are either off-line, or
require human action to sign the zone, or policy requires someone to
check the data before its added to the zone (e.g. for child NS
records). When an update becomes available (e.g. when the parent
server verifies and accepts the NOTIFY), the server MUST notify an
administrator by email or other appropriate method of the pending
action. It must repeat that notification at a configurable interval
(e.g. once a day) until the adminstrator takes action to approve or
reject the change.
Once the changes are approved and signed, the new records are
published to the DNS.
2.1.3 Parent Pull
In the "Parent Pull" model, the child to parent NOTIFY acts like the
master to secondary NOTIFY works currently. E.g. the parent takes the
NOTIFY as a request to gather data to update its zone. The parent,
on its own schedule, retrieves the NS or KEY records from the child
and compares them to what it current has. If there are differences,
the parent copies or generates replacement records (i.e. the DS
records which map to the child KEY records), signs them, and
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publishes them. As above, this can proceed either manually or
automatically.
2.2 Update of Parent DS Records
The DS records held in the parent zone are derived from the KEY
records originated by the child. They are also protected under a key
held by the parent zone. Upon receipt of the NOTIFY indicating a
child KEY change, and after any other queries required (e.g. to
retrieve copies of the KEY or NS records from the child), the parent
forms a new DS RRSet consisting only of DS's which point to the
current set of child SEP KEY records. This new DS RRSet, after it is
signed, replaces the current DS RRSet held by the parent server in
its entirety.
2.3 Update of Parent NS Records
Since the parent zone's copies of the NS records for the child zone
are not signed, it is a simple matter of policy as to whether the
update of the NS records requires human intervention, or can be done
automatically upon receipt of the NOTIFY. This should be a
configurable item, and the action should default to automatic.
The parent zone MUST verify the names pointed to by the NS are
resolvable, that at least one name points to a server not named in
the child zone, and that it has glue A records for any server named
in the child zone. [Q: Does this make sense, or is it better to just
trust the child?] If these conditions are not satisfied, the parent
server MUST NOT install the new records, and MUST log the problem.
It must also return an error code of ??
The set of glue NS records held by the parent which point to the
child MUST be replaced in their entirety by the new set of NS records
provided either in the notify, or by retrieval by the parent server
from the child.
2.4 Uncommitted Updates
If a parent zone has a uncommitted update of child information (e.g.
because policy requires manual intervention to approve the update),
it MUST discard that update upon validated receipt of a new NOTIFY
covering the information to be updated. I.e., if the new NOTIFY
covers NS records, discard any previous uncommitted updates to the NS
RRSet.
3. Parent Zone Secondary Server Update
Once the adminstrator of the parent zone has accepted the changes
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(either automatically, or by specific action), the parent zone
records on the primary server MUST be updated, and, if policy allows,
the primary SHOULD do a DNS NOTIFY to the secondary servers
indicating the change to the NS or DS records.
4. Security Considerations
The security of this mechanism is directly related to the protection
afforded the private keys of the parent and child zones. Compromise
of the child zone keys can result in incorrect information being
added to both the parent and child zones. It could also result in
additional denial of service threats to the parent servers in that
the servers could be tied up validating and processing bogus (but
authenticated) update requests for the compromised child zone.
Normative References
[DSREC] Gudmundsson, O., "Delegation Signer Resource Record", ID
draft-ietf-dnsext-delegation-signer-14.txt, May 2003,
<http://www.ietf.org/internet-drafts/
draft-ietf-dnsext-delegation-signer-14.txt>.
[RFC1996] Vixie, P., "A Mechanism for Prompt Notification of Zone
Changes (DNS NOTIFY)", RFC 1996, August 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2535] Eastlake, D., "Domain Name System Security Extensions",
RFC 2535, March 1999.
[RFC2931] Eastlake, D., "DNS Request and Transaction Signatures (
SIG(0)s)", RFC 2931, September 2000.
[SEPFLAG] Kolkman, O., "KEY RR Secure Entry Point (SEP) Flag", ID
draft-ietf-dnsext-keyrr-key-signing-flag-07.txt, January
2003, <http://www.ietf.org/internet-drafts/
draft-ietf-dnsext-keyrr-key-signing-flag-07.txt>.
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Author's Address
Michael StJohns
Nominum, Inc.
2385 Bay Road
Redwood City, CA 94063
USA
Phone: +1-301-528-4729
EMail: Mike.StJohns@nominum.com
URI: www.nominum.com
Appendix A. Discussion: NOTIFY vs UPDATE & Push vs Pull
During the pre-publication phase, the author solicited comments on
this draft. One email made two suggestions. The first was to use
UPDATE instead of NOTIFY, the second was if NOTIFY was used then to
use the notify/pull model for update rather than the mode proposed
here of pushing the data as part of the NOTIFY.
On the subject of NOTIFY vs UPDATE, neither has exactly the model
described here, but NOTIFY comes closer. UPDATE has semantics that
says "please update your copy of something that I own with this
information that I've provided." NOTIFY's semantics are "something's
changed that you may care about." What we really want is
"something's changed that I own, that may affect something that you
own and here's the data that's changed." NOTIFY is probably the
closest to this meaning.
On the subject of push vs pull, either of these two models would
work, and the pull model (ala the original NOTIFY RFC) should be the
fall back if data isn't provided as part of the secured NOTIFY. If
the data is provided and secured (i.e. signed) in the NOTIFY, the
parent shouldn't actually have to retrieve data from the child zone
(unless the NOTIFY is truncated). If the NOTIFY isn't signed, then
the pull model is the only one that will work, but then there's no
point in actually writing this document. In general, the author
would like to minimize the work factor for the parent and keeping
track of which child zones need to be polled could be expensive,
especially in very large parent zones. Placing the burden on the
child to push data to the parent seems a better choice.
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