Internet DRAFT - draft-mccallum-kitten-krb-service-discovery
draft-mccallum-kitten-krb-service-discovery
Internet Engineering Task Force N. McCallum
Internet-Draft M. Rogers
Updates: 4120 (if approved) Red Hat, Inc.
Intended status: Standards Track September 23, 2016
Expires: March 27, 2017
Kerberos Service Discovery using DNS
draft-mccallum-kitten-krb-service-discovery-03
Abstract
This document proposes defines a new mechanism for discovering
Kerberos services using DNS. This new mechanism extends the
mechanism already defined in Kerberos V5 [RFC4120] and has four
goals. First, reduce the number of DNS queries required to discover
a Kerberos KDC. Second, provide DNS administrators more control over
client behavior. Third, provide support for discovery of the MS-
KKDCP transport. Fourth, define a discovery procedure for Kerberos
password services.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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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."
This Internet-Draft will expire on March 27, 2017.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Document Conventions . . . . . . . . . . . . . . . . . . . . 3
3. Realm to Domain Translation . . . . . . . . . . . . . . . . . 3
4. Required URI Format . . . . . . . . . . . . . . . . . . . . . 3
4.1. Scheme . . . . . . . . . . . . . . . . . . . . . . . . . 3
4.2. Flags . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4.2.1. Master Flag . . . . . . . . . . . . . . . . . . . . . 4
4.3. Transport . . . . . . . . . . . . . . . . . . . . . . . . 4
4.4. Residual . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Kerberos V5 KDC Service Discovery . . . . . . . . . . . . . . 4
6. Kerberos Password Service Discovery . . . . . . . . . . . . . 4
7. Kerberos Admin Service Discovery . . . . . . . . . . . . . . 5
8. Relationship to Existing Mechanism . . . . . . . . . . . . . 5
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
9.1. Kerberos Server Discovery Flags . . . . . . . . . . . . . 5
9.1.1. Registration Template . . . . . . . . . . . . . . . . 5
9.1.2. Initial Registry Contents . . . . . . . . . . . . . . 6
9.2. Kerberos Server Discovery Transport Types . . . . . . . . 6
9.2.1. Registration Template . . . . . . . . . . . . . . . . 6
9.2.2. Initial Registry Contents . . . . . . . . . . . . . . 6
10. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. URI Format Examples . . . . . . . . . . . . . . . . . . 7
11. Normative References . . . . . . . . . . . . . . . . . . . . 7
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Section 7.2.3 of Kerberos V5 [RFC4120] defines a procedure for
discovering a KDC based on DNS SRV records. This method has three
drawbacks. First, two DNS queries are required to locate a single
service (one for UDP and one for TCP). Second, specifying UDP and
TCP in separate records means that the DNS administrator has no
control over client preferences for TCP or UDP. Third, any new
transports for reaching the KDC (such as MS-KKDCP) will require new
records and additional DNS queries.
The Kerberos Password [RFC3244] protocol has no defined procedure for
discovery similar to the KDC method described above. Implementations
have largely chosen a similar method to section 7.2.3 of Kerberos V5
[RFC4120], inheriting the same drawbacks outlined above.
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This RFC defines three new URI DNS records [RFC7553]; one each for
KDC, Kerberos Password, and Kerberos Admin service discovery.
2. Document Conventions
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 RFC 2119 [RFC2119].
3. Realm to Domain Translation
This document does not define a new mechanism for translating
Kerberos realms to DNS domains. The existing mechanism as defined in
section 7.2.3.1 of Kerberos V5 [RFC4120] MUST be followed.
4. Required URI Format
The following URI format MUST be supported by clients.
The URI format is comprised of text fields delimited by a colon (":")
character.
krb5srv:[flags]:transport:residual
See the Appendix for examples.
4.1. Scheme
This field identifies the URI scheme. Its value MUST be the string
"krb5srv".
4.2. Flags
This field contains a sequence of zero or more case-insensitive
characters used individually to convey server attributes or feature
support (eg. "XYZ" indicates support for features X, Y, and Z.) for
the purpose of organizing the lookup results.
This field MUST be present even when no flags are provided, appearing
as two colons seperating the scheme and transport fields (eg.
"krb5srv::tcp:host").
Flags are not considered critical, therefore flags that are not used
or unknown to the implementation SHOULD be ignored.
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4.2.1. Master Flag
The "m" flag signifies that the discovered server is a master server.
The client SHOULD consider this server as one that would immediately
see password changes and use it as a fallback for incorrect password
errors.
4.3. Transport
This field contains a string to indicate the transport method to use
when contacting the host specified in the URI.
4.4. Residual
This field contains information specific to the transport. It may
contain sub-fields where such are defined in the transport
specification.
5. Kerberos V5 KDC Service Discovery
In order to discover a KDC service location, the client MUST query
the following URI DNS [RFC7553] record (REALM indicates the
translation of the Kerberos realm to a DNS domain):
_kerberos.REALM
TTL, Class, URI, Priority, Weight and Target have the standard
meanings as defined in RFC 2782 [RFC2782] and the URI DNS record type
[RFC7553]. Target SHOULD contain one of the URI formats specified in
this document.
6. Kerberos Password Service Discovery
In order to discover a password service location, the client MUST
query the following URI DNS [RFC7553] record (REALM indicates the
translation of the Kerberos realm to a DNS domain):
_kpasswd.REALM
TTL, Class, URI, Priority, Weight and Target have the standard
meanings as defined in RFC 2782 [RFC2782] and the URI DNS record type
[RFC7553]. Target SHOULD contain one of the URI formats specified in
this document.
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7. Kerberos Admin Service Discovery
In order to discover an admin service location, the client MUST query
the following URI DNS [RFC7553] record (REALM indicates the
translation of the Kerberos realm to a DNS domain):
_kerberos-adm.REALM
TTL, Class, URI, Priority, Weight and Target have the standard
meanings as defined in RFC 2782 [RFC2782] and the URI DNS record type
[RFC7553]. Target SHOULD contain one of the URI formats specified in
this document.
8. Relationship to Existing Mechanism
If an existing discovery protocol is supported by a client, the
client SHOULD perform the URI lookup as defined in this document
first. If no URI record is found, the client MAY attempt discovery
using another protocol.
9. IANA Considerations
This document establishes two registries with the following
procedure, in accordance with [RFC5226]:
Registry entries are to be evaluated using the Specification Required
method. All specifications must be be published prior to entry
inclusion in the registry. There will be a three-week review period
by Designated Experts on the kitten@ietf.org mailing list. Prior to
the end of the review, the Designated Experts must approve or deny
the request. This decision is to be conveyed to both the IANA and
the list, and should include reasonably detailed explanation in the
case of a denial as well as whether the request can be resubmitted.
9.1. Kerberos Server Discovery Flags
This section species the IANA "Kerberos Server Discovery Flags"
registry. This registry records the value and description for each
flag.
9.1.1. Registration Template
Value: A single unique ASCII character that identifies the entry,
excluding the colon character (":") since it is used as a field
delimiter in the scheme outlined in this document.
Description: A brief description of the meaning of the value when it
appears in the flags field.
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Reference: A reference to the details of the flag.
9.1.2. Initial Registry Contents
o Value: m
o Description: The target is a master server.
o Reference: TBD
9.2. Kerberos Server Discovery Transport Types
This section specifies the IANA "Kerberos Server Discovery Transport
Types" registry. This registry records the value, description,
residual format, case-sensitive residual elements, default ports, and
a reference for each type.
9.2.1. Registration Template
Value: A unique value to identify the transport type within the
transport field.
Description: The name or description of the transport type.
Residual Format: The format of the residual field that specifies the
discovered target URL. Optional parts of the URL are enclosed in
brackets.
Case Sensitive: If any part of the residual format is case-
sensitive, it is specified here.
Default KDC Port: A number in the range of 1-65535 as the port used
to contact the target URL when no port is specified and the lookup
result is for a Kerberos server.
Default Admin Service Port: A number in the range of 1-65535 as the
port used to contact the target URL when no port is specified and
the lookup result is for a Kerberos Admin server.
Default Password Service Port: A number in the range of 1-65535 as
the port used to contact the target URL when no port is specified
and the lookup result is for a Kerberos Password server.
Reference: A reference to the details of the transport type.
9.2.2. Initial Registry Contents
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o Value: "udp"
o Description: User Datagram Protocol
o Residual Format: "host[:port]"
o Case Sensitive: None
o Default KDC Port: 88
o Default Admin Service Port: 749
o Default Password Service Port: 464
o Reference: [RFC0768]
o Value: "tcp"
o Description: Transport Control Protocol
o Residual Format: "host[:port]"
o Case Sensitive: None
o Default KDC Port: 88
o Default Admin Service Port: 749
o Default Password Service Port: 464
o Reference: [RFC0793]
o Value: "kkdcp"
o Description: Kerberos Key Distribution Center Proxy Protocol
o Residual Format: https://host[:port][/path]
o Case Sensitive: [/path]
o Default KDC Port: 443
o Default Admin Service Port: 443
o Default Password Service Port: 443
o Reference: [MS-KKDCP]
10. Appendix
10.1. URI Format Examples
o krb5srv:m:kkdcp:https://kdc.example.com:8080/path
o krb5srv:m:udp:kdc.example.com
o krb5srv::kkdcp:https://kdc2.example.com/path
o krb5srv::tcp:192.168.1.20:1000
11. Normative References
[MS-KKDCP]
Microsoft, "[MS-KKDCP]: Kerberos Key Distribution Center
(KDC) Proxy Protocol", May 2014,
<http://msdn.microsoft.com/en-us/library/hh553774.aspx>.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<http://www.rfc-editor.org/info/rfc768>.
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[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<http://www.rfc-editor.org/info/rfc793>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
DOI 10.17487/RFC2782, February 2000,
<http://www.rfc-editor.org/info/rfc2782>.
[RFC3244] Swift, M., Trostle, J., and J. Brezak, "Microsoft Windows
2000 Kerberos Change Password and Set Password Protocols",
RFC 3244, DOI 10.17487/RFC3244, February 2002,
<http://www.rfc-editor.org/info/rfc3244>.
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120,
DOI 10.17487/RFC4120, July 2005,
<http://www.rfc-editor.org/info/rfc4120>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC7553] Faltstrom, P. and O. Kolkman, "The Uniform Resource
Identifier (URI) DNS Resource Record", RFC 7553,
DOI 10.17487/RFC7553, June 2015,
<http://www.rfc-editor.org/info/rfc7553>.
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Appendix A. Acknowledgements
Simo Sorce (Red Hat)
Nico Williams (Cryptonector)
Authors' Addresses
Nathaniel McCallum
Red Hat, Inc.
100 East Davie Street
Raleigh, NC 27601
USA
EMail: npmccallum@redhat.com
Matt Rogers
Red Hat, Inc.
100 East Davie Street
Raleigh, NC 27601
USA
EMail: mrogers@redhat.com
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