Internet DRAFT - draft-hardaker-dnsop-csync
draft-hardaker-dnsop-csync
DNSOP W. Hardaker
Internet-Draft Parsons, Inc.
Intended status: Standards Track October 21, 2013
Expires: April 24, 2014
Child To Parent Synchronization in DNS
draft-hardaker-dnsop-csync-02
Abstract
This document specifies how a child zone in the DNS can publish a
record to indicate to a parental agent that it may copy and process
certain records from the child zone. The existence and change of the
record may be monitored by a parental agent, after which the parent
may act on the data appropriately.
Status of this Memo
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This Internet-Draft will expire on April 24, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology Used in This Document . . . . . . . . . . . . 3
2. Definition of the CSYNC RRType . . . . . . . . . . . . . . . . 4
2.1. The CSYNC Resource Record Format . . . . . . . . . . . . . 4
2.1.1. The CSYNC Resource Record Wire Format . . . . . . . . 4
2.1.2. The CSYNC Presentation Format . . . . . . . . . . . . 6
2.1.3. CSYNC RR Example . . . . . . . . . . . . . . . . . . . 6
2.2. CSYNC Data Processing . . . . . . . . . . . . . . . . . . 7
2.2.1. Processing Procedure . . . . . . . . . . . . . . . . . 7
2.2.2. CSYNC Record Types . . . . . . . . . . . . . . . . . . 8
2.3. Operational Considerations . . . . . . . . . . . . . . . . 9
2.3.1. Error Reporting . . . . . . . . . . . . . . . . . . . 9
2.3.2. Child Nameserver Selection . . . . . . . . . . . . . . 9
2.3.3. Documented Parental Agent Type Support . . . . . . . . 10
2.3.4. Other Considerations . . . . . . . . . . . . . . . . . 10
3. Security Considerations . . . . . . . . . . . . . . . . . . . 10
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. Normative References . . . . . . . . . . . . . . . . . . . 11
6.2. Informative References . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
This document specifies how a child zone in the DNS can publish a
record to indicate to a parental agent that it may copy and process
certain records from the child zone. The existence and change of the
record may be monitored by a parental agent, after which the parent
may act on the data appropriately.
Some resource records (RRs) in a parent zone are typically expected
to be in-sync with the source data in the child's zone. The most
common records, to date, that should match are the nameserver (NS)
records and any necessary associated address "glue" records (A and
AAAA). These records are referred to as "delegation records".
It has been traditionally challenging for children to update their
delegation records within the parent's set in a timely fashion. This
difficulty is frequently from simple operator laziness or because of
the complexities of maintaining a large number of DNS zones. Having
an automated mechanism for signaling updates will greatly ease the
child zone operator's maintenance burden and improve the robustness
of the DNS as a whole.
This draft introduces a new RR type (RRType) named "CSYNC" that
indicates which delegation records published by a child should be
processed by a parental agent and used to update the parent zone's
DNS data.
This specification does not address how to perform bootstrapping
operations to get the required initial DNSSEC-secured operating
environment in place. Additionally, this specification was not
designed to synchronize DNSSEC security records, such as DS pointers.
For such a solution, please see the complimentary solution
[I-D.kumari-ogud-dnsop-cds] for maintaining security delegation
information.
1.1. Terminology Used in This Document
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].
This document is aimed at the case where there is an organizational
separation of the child and parent. In this case there are many
different operating situations. A common case is the Registrant/
Registrar/Registry relationship, used by many Top Level Domains in
the DNS. In this case, the parent consists of Registrar and
Registry, with different rules about what each can do or not do. To
remain operating model neutral we will use the neutral word "Parental
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Agent" as the entity that uses results of DNS queries discussed in
this document to update the delegation records into the parent zone.
The entity that performs the changes in the the DNS is called "DNS
Publisher".
2. Definition of the CSYNC RRType
The CSYNC RRType contains, in its RDATA component, these parts: an
SOA serial number, a set of flags and a simple bit-list indicating
the DNS RRTypes in the child that should be processed by the parental
agent in order to modify the DNS delegation records for the child
within the parent's zone. Children wanting a parental agent to
perform the synchronization steps outlined in this document MUST
publish a CSYNC record at the apex of the child zone. Parental agent
implementations MAY choose to query child zones for this record and
process DNS record data as indicated by the Type Bit Map field in the
RDATA of the CSYNC record. How the data is processed is described
later in Section Section 2.2.
Parental agents MUST process the entire set of child data indicated
by the Type Bit Map field (i.e., all record types indicated along
with all of the necessary records to support processing of that type)
or else parental agents MUST NOT make any changes to parental records
at all. Errors due to unsupported Type Bit Map bits or otherwise
nonpunishable data SHALL result in no change to the parent zone's
delegation information for the child. Parental agents MUST ignore a
child's CSYNC RDATA set if multiple CSYNC resource records are found;
only a single CSYNC record should ever be expected.
The parental agent MUST perform DNSSEC validation of the CSYNC RRType
data and MUST perform DNSSEC validation of any data to be copied from
the child to the parent. Parents MUST not process any data from any
of these records if any of the validation results indicate any
anything other than "Secure" [RFC4034].
2.1. The CSYNC Resource Record Format
2.1.1. The CSYNC Resource Record Wire Format
The CSYNC RDATA consists of the following fields:
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1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SOA Serial |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Type Bit Map /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Type Bit Map (continued) /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2.1.1.1. The SOA Serial Field
The SOA Serial field contains a copy of the 32-bit SOA serial number
from the child zone. If the value is non-zero, parental agents
querying children's authoritative servers MUST NOT act on data from
zones advertising an SOA serial number less than this value. A
special value of 0 indicates that no such restriction is in place.
Note that a child zone's current SOA serial number may be greater
than the number indicated by the CSYNC record. A child SHOULD update
the SOA Serial field in the CSYNC record every time the data being
referenced by the CSYNC record is changed (e.g. an NS record or
associated address record is changed). A child MAY choose to update
the SOA Serial field to always match the current SOA serial field.
Parental agents MAY cache SOA serial numbers from data they use and
refuse to process data from zones older than the last instance they
pulled data from.
2.1.1.2. The Flags Field
The Flags field contains 16 bits of flags defining operations that
affect the processing of the CSYNC record. The flags defined in this
document are as follows:
0x00 0x01: "immediate"
The definitions for how the flags are to be used can be found later
in Section Section 2.2.
The remaining flags are reserved for use by future specifications.
Undefined flags MUST be set to 0 by CSYNC publishers. Parental
agents MUST NOT process a CSYNC record if it contains a 1 value for a
flag that is unknown to or unsupported by the parental agent.
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2.1.1.2.1. The Type Bit Map Field
The Type Bit Map field indicates the record types to be processed by
the parental agent, according to the procedures in Section
Section 2.2. The Type Bit Map field is encoded in the same way as
the Type Bit Maps field of the NSEC record, described in [RFC4034],
Section 4.1.2. If a bit has been set that a parental agent
implementation does not understand, the parental agent MUST NOT act
upon the record. Specifically: a parental agent must not copy data
blindly; An IETF proposed (or higher) standard specification must
exist that defines how the data should be processed for a given bit.
2.1.2. The CSYNC Presentation Format
The CSYNC presentation format is as follows:
The SOA Serial field is represented as an integer.
The Flags field is represented as an integer.
The Type Bit Map field is represented as a sequence of RR type
mnemonics. When the mnemonic is not known, the TYPE
representation described in [RFC3597], Section 5, MUST be used.
Implementations that support parsing of presentation format
records SHOULD be able to read and understand these TYPE
representations as well.
2.1.3. CSYNC RR Example
The following CSYNC RR shows an example entry for "example.com" that
indicates the NS, A and AAAA bits are set and should be processed by
the parental agent for example.com. The parental agent should pull
data only from a zone using a minimum SOA serial number of 66 (0x42
in hexadecimal).
example.com. 3600 IN CSYNC 66 1 A NS AAAA
The RDATA component of the example CSYNC RR would be encoded on the
wire as follows:
0x00 0x00 0x00 0x42 (SOA Serial)
0x00 0x01 (Flags [the immediate bit is set])
0x00 0x04 0x60 0x00 0x00 0x08 (Type Bit Map)
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2.2. CSYNC Data Processing
The CSYNC record and associated data must be processed as an "all or
nothing" operation set. If a parental agent fails to successfully
query for any of the required records, the whole operation MUST be
aborted. (Note that a query resulting in "no records exist" as
proven by NSEC or NSEC3 is to be considered successful).
Parental agents MAY:
Process the CSYNC record immediately after noticing it if the
"immediate" flag is set. If the "immediate" flag is not set, the
parental agent MUST not act until the zone administrator approves
the operation through an out-of-band mechanism (such as through
pushing a button via a web interface).
Require that the child zone administrator approve the operation
through an out-of-band mechanism (such as through pushing a button
via a web interface). I.e., a parental agent MAY choose not to
support the "immediate" flag.
Note: how the approval is done out-of-band is outside the scope of
this document and is implementation-specific to parental agents.
2.2.1. Processing Procedure
The following shows a sequence of steps that SHOULD be used when
collecting and processing CSYNC records from a child zone. Because
DNS queries are not allowed to contain more than one "question" at a
time, a sequence of requests is needed. When processing a CSYNC
transaction request, all DNS queries should be sent to a single
authoritative name server for the child zone. To ensure a single
host is being addressed, DNS over TCP SHOULD be used to avoid
conversing with multiple nodes at an anycast address.
1. Query for the child zone's SOA record
2. Query for the child zone's CSYNC record
3. Query for the child zone's data records, as required by the CSYNC
record's Type Bit Map field
4. Query for the child zone's SOA record again
If the SOA records from the first and last steps have different
serial numbers, then the CSYNC record obtained in the second set MUST
NOT be processed.
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If the SOA serial numbers are equal but less than the CSYNC record's
SOA Serial Field, the record MUST NOT be processed. If state is
being kept by the parental agent and the SOA serial number is less
than the last time a CSYNC record was processed, this CSYNC record
SHOULD NOT be processed. Similarly, if state is being kept by the
parental agent and the SOA Serial Field of the CSYNC record is less
than the SOA Serial Field of the CSYNC record from last time, then
this CSYNC record SHOULD NOT be processed.
If DNSSEC fails to validate all of the data returned for these
queries as "secure", then this CSYNC record MUST NOT be processed.
See the "Operational Consideration" section (Section Section 2.3) for
additional guidance about processing.
2.2.2. CSYNC Record Types
This document defines how the following record types may be processed
if the CSYNC Type Bit Map field indicates they should be processed.
2.2.2.1. The NS type
The NS type flag indicates that the NS records from the child zone
should be copied into the parent's delegation information records for
the child.
NS records found within the child's zone should be copied verbatim
and the result published within the parent zone should be an exact
matching set of NS records. If the child has published a new NS
record within their set, this record should be added to the parent
zone. Similarly, if NS records in the parent's delegation records
for the child contain records that have been removed in the child's
NS set, then they should be removed in the parent's set as well.
Parental agents MAY refuse to perform NS updates if the replacement
records fail to meet NS record policies required by the parent zone
(e.g. "every child zone must have at least 2 NS records").
2.2.2.2. The A and AAAA types
The A and AAAA type flags indicates that the A and AAAA,
respectively, address glue records for in-bailiwick NS records within
the child zone should be copied into the parent's delegation
information.
Queries should be sent by the parental agent to determine the A and
AAAA record addresses for each NS record within a NS set for the
child that are in-bailiwick.
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Note: only the matching types should be queried. E.g., if the AAAA
bit has not been set, then the AAAA records (if any) in the parent's
delegation should remain as is. If a given address type is set and
the child's zone contains no data for that type (as proven by
appropriate NSEC or NSEC3 records), then the result in the parent's
delegation records for the child should be an empty set.
The procedure for querying for A and AAAA records MUST occur after
the procedure, if required, for querying for NS records as defined in
Section Section 2.2.2.1. This ensures that the right set NS records
is used as provided by the current NS set of the child. I.e, for
CSYNC records that have the NS bit set, the NS set used should be the
ones pulled from the child while processing the CSYNC record. For
CSYNC records without the NS bit set, the existing NS records within
the parent should be used to determine which A and/or AAAA records to
update.
2.3. Operational Considerations
There are a number of important things to consider when deploying a
CSYNC RRType.
2.3.1. Error Reporting
There is no inline mechanism for a parental agent to report errors to
operators of child zones. Thus, the only error reporting mechanisms
must be out of band, such as through a web console or over email.
Child operators utilizing the "immediate" flag that fail to see an
update within the parental agent's specified operational window
should access the parental agent's error logging interface to
determine why an update failed to be processed.
2.3.2. Child Nameserver Selection
Parental agents will need to poll child nameservers in search of
CSYNC records and related data records.
Parental agents MAY perform best-possible verification by querying
all NS records for available data to determine which has the most
recent SOA and CSYNC version (in an ideal world, they would all be
equal but this is not possible in practice due to synchronization
delays and transfer failures).
Parental agents MAY offer a configuration interface to allow child
operators to specify which nameserver should be considered the master
to send data queries too. This master may not be one of the
publically listed nameservers in the NS set (i.e., it may be a
"hidden master").
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2.3.3. Documented Parental Agent Type Support
Parental agents that support processing CSYNC records SHOULD publicly
document the following minimum processing characteristics:
The fact that they support CSYNC processing
The Type Bit Map bits they support
The frequency with which they poll clients (which MAY also be
configurable by the client)
If they support the "immediate" flag
If they poll a child's single nameserver, a configured list of
nameservers, or all of the advertised nameservers when querying
records
If they support SOA serial number caching to avoid issues with
regression and/or replay
Where errors for CSYNC processing are published
If they support sending queries to a "hidden master".
2.3.4. Other Considerations
XXX: Discuss complete replacement scenarios and if allowed.
3. Security Considerations
This specification requires the use of DNSSEC in order to determine
that the data being updated was unmodified by third-parties.
Parental agents implementing CSYNC processing MUST ensure all DNS
transactions are validated by DNSSEC as "secure". Clients deploying
CSYNC MUST ensure their zones are signed, current and properly linked
to the parent zone with a DS record that points to an appropriate
DNSKEY of the child's zone.
This specification does not address how to perform bootstrapping
operations to get the required initial DNSSEC-secured operating
environment in place. Additionally, this specification was not
designed to synchronize DNSSEC security records, such as DS pointers.
For such a solution, please see the complimentary solution
[I-D.kumari-ogud-dnsop-cds] for maintaining security delegation
information.
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4. IANA Considerations
TBD
5. Acknowledgments
A thank you goes out to Warren Kumari and Olafur Gu[eth]mundsson,
who's work on the CDS record type helped inspire the work in this
document, as well as the definition for "Parental Agent" and "DNS
Publisher" definitions. A thank you also goes out to Ed Lewis, who
the author held many conversations with about the issues surrounding
parent/child relationships and synchronization. Much of the work in
this document is derived from the careful existing analysis of these
three esteemed colleagues.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record
(RR) Types", RFC 3597, September 2003.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, March 2005.
6.2. Informative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, March 2005.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, March 2005.
[I-D.kumari-ogud-dnsop-cds]
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Kumari, W., Gudmundsson, O., and G. Barwood, "Automating
DNSSEC delegation trust maintenance",
draft-kumari-ogud-dnsop-cds-05 (work in progress),
October 2013.
Author's Address
Wes Hardaker
Parsons, Inc.
P.O. Box 382
Davis, CA 95617
US
Phone: +1 530 792 1913
Email: ietf@hardakers.net
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