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Versions: 00 01 02 03 draft-ietf-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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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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