Internet DRAFT - draft-sakane-dhc-dhcpv6-kdc-option
draft-sakane-dhc-dhcpv6-kdc-option
Network Working Group S. Sakane
Internet-Draft Cisco Systems
Intended status: Standards Track M. Ishiyama
Expires: March 17, 2013 Toshiba Corporation
September 13, 2012
Kerberos Options for DHCPv6
draft-sakane-dhc-dhcpv6-kdc-option-18.txt
Abstract
This document defines four new options for the Dynamic Host
Configuration Protocol for IPv6 (DHCPv6). These options are used to
carry coniguration information for Kerberos.
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 17, 2013.
Copyright Notice
Copyright (c) 2012 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
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.
Sakane & Ishiyama Expires March 17, 2013 [Page 1]
Internet-Draft Kerberos Options for DHCPv6 September 2012
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . 4
3. Kerberos Options . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Kerberos Principal Name Option . . . . . . . . . . . . . . 5
3.2. Kerberos Realm Name Option . . . . . . . . . . . . . . . . 6
3.3. Kerberos Default Realm Name Option . . . . . . . . . . . . 6
3.4. Kerberos KDC Option . . . . . . . . . . . . . . . . . . . 6
4. Client and Server Operation . . . . . . . . . . . . . . . . . 9
4.1. KDC discovery for a client . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Normative References . . . . . . . . . . . . . . . . . . . 13
8.2. Informative References . . . . . . . . . . . . . . . . . . 13
Appendix A. An example of the operation of the client . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
Sakane & Ishiyama Expires March 17, 2013 [Page 2]
Internet-Draft Kerberos Options for DHCPv6 September 2012
1. Introduction
Kerberos Version 5 [RFC4120] is a trusted third-party authentication
system. Each organization wishing to use Kerberos establishes its
own "realm" and each client is registered as part of that realm. At
least one Key Distribution Center (KDC) is required for the operation
of a Kerberos realm.
When a client wishes to communicate with, and be authenticated to, a
Kerberos application server (also a client of the KDC), the client
identifies itself, and its realm, to the KDC and acquires a
credential from the KDC. The client then presents the credential to
the Kerberos application server which can use the credential to
authenticate the client. The client needs to know at least one IP
address for a KDC in order to initiate this process.
One example of the application of this protocol is as follows. A
student might want to use a shared, public workstation, one that is
not configured for Kerberos. If there is a mechanism for the
workstation to obtain a realm name and IP address for a KDC, then a
student need only input a user-id and pass phrase to be able to use
Kerberos.
The Kerberos V5 specification [RFC4120] defines the use of DNS SRV
records [RFC2782] for KDC discovery. Some systems, such as
industrial systems, do not use DNS. Such systems already have their
own name spaces and their own name resolution systems, including pre-
configured mapping tables for devices, and do not use Fully Qualified
Domain Names. However, many of these systems do use DHCP.
Adding a DNS server to such systems may decrease the reliability of
the system and increase the management cost. In such an environment,
another mechanism is needed to provide an IP address for the KDC.
For the PacketCable Architecture [PCARCH], RFC 3634 [RFC3634] defines
the KDC Server Address sub-option for the DHCPv4 CableLabs Client
Configuration option. However, a mechanism is still needed to
provide a realm name and an IPv6 address, one which does not depend
on any external architecture.
This document defines a Kerberos option for DHCPv6 which provides a
realm name and/or a list of KDC IP addresses. This option does not
replace or modify any of the existing methods for obtaining this
information.
Sakane & Ishiyama Expires March 17, 2013 [Page 3]
Internet-Draft Kerberos Options for DHCPv6 September 2012
2. Conventions 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 RFC 2119 [RFC2119].
It is assumed that the readers are familiar with the terms and
concepts described in DHCPv6 [RFC3315], Kerberos V5 [RFC4120], and
DNS SRV [RFC2782].
Sakane & Ishiyama Expires March 17, 2013 [Page 4]
Internet-Draft Kerberos Options for DHCPv6 September 2012
3. Kerberos Options
This document defines four DHCPv6 configuration parameters for
Kerberos.
Kerberos Principal Name Option
Kerberos Realm Name Option
Kerberos Default Realm Name Option
Kerberos KDC Option
This section describes the format of each option, and the usage of
each field in that option.
These options except of the Kerberos KDC Option MUST NOT appear more
than once in a DHCPv6 message.
3.1. Kerberos Principal Name Option
The Kerberos Principal Name Option carries the name of a Kerberos
principal. This is sent by the client to the DHCPv6 server which MAY
use it to select a specific set of configuration parameters, either
for a client or for a Kerberos application server.
The format of the Kerberos Principal Name option is:
0 1 2 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_KRB_PRINCIPAL_NAME | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: principal-name :
: (variable length) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o option-code (16-bit): OPTION_KRB_PRINCIPAL_NAME (TBD by IANA)
o option-len (16-bit): length of the principal-name field.
o principal-name (variable): a client principal name. The encoding
of the principal-name field MUST conform to the definition of
"PrincipalName" in section 5.2.2 of RFC 4120 [RFC4120].
Sakane & Ishiyama Expires March 17, 2013 [Page 5]
Internet-Draft Kerberos Options for DHCPv6 September 2012
3.2. Kerberos Realm Name Option
The Kerberos Realm Name Option carries a Kerberos realm name. A
DHCPv6 client uses this option to specify to a DHCPv6 server which
realm the client wants to access.
The format of the Kerberos Realm Name option is:
0 1 2 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_KRB_REALM_NAME | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: realm-name :
: (variable length) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o option-code (16-bit): OPTION_KRB_REALM_NAME (TBD by IANA)
o option-len (16-bit): the length of the realm-name field in octets.
o realm-name (variable): a realm-name. The encoding of the realm-
name field MUST conform to the definition of "Realm" in section
5.2.2 of RFC 4120 [RFC4120].
3.3. Kerberos Default Realm Name Option
The Kerberos Default Realm Name Option is used to specify a default
realm name for the Kerberos system. A DHCPv6 server uses this option
to specify the default realm name to both clients and Kerberos
application servers.
The option-code of this option is OPTION_KRB_DEFAULT_REALM_NAME (TBD
by IANA). The format and usage of the option-len and realm-name
fields are identical to those for the Kerberos Realm Name Option.
3.4. Kerberos KDC Option
The Kerberos KDC Option is used to provide configuration information
about a KDC.
The format of the Kerberos KDC Option is:
Sakane & Ishiyama Expires March 17, 2013 [Page 6]
Internet-Draft Kerberos Options for DHCPv6 September 2012
0 1 2 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_KRB_KDC | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transport Type| Port Number | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
| |
| KDC IPv6 address +---------------+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ :
: :
: realm-name :
: (variable length) :
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o option-code (16-bit): OPTION_KRB_KDC (TBD by IANA)
o option-len (16-bit): 23 + the length of the realm-name field in
octets.
o Priority (16-bit): see the description of Weight field.
o Weight (16-bit): the Priority and Weight fields provide a hint to
the client as to which KDC to select. The usage of the Priority
and Weight values MUST follow the specification for DNS SRV
[RFC2782].
o Transport Type (8-bit): The Transport Type specifies the transport
protocol used for Kerberos. Kerberos [RFC4120] defines UDP and
TCP transports. Exchanges over TCP are further described in
[RFC5021] while the transport of Kerberos over TLS is described in
[RFC6251].
The transport type is defined in below.
Value Transport Type
---- --------------
0 Reserved
1 UDP
2 TCP
3 TLS
Sakane & Ishiyama Expires March 17, 2013 [Page 7]
Internet-Draft Kerberos Options for DHCPv6 September 2012
4-254 Unassigned
255 Reserved
o Port Number (16-bit): the port number on which the KDC listens.
o KDC IPv6 address (128-bit): the IPv6 address of the KDC.
o realm-name (variable): the name of the realm for which the
specified KDC provides service. The encoding of the realm- name
field MUST conform to the definition of "Realm" in section 5.2.2
of RFC 4120 [RFC4120].
Sakane & Ishiyama Expires March 17, 2013 [Page 8]
Internet-Draft Kerberos Options for DHCPv6 September 2012
4. Client and Server Operation
This section describes the operations of client and server. It
assumes that the client has been configured with a principal name.
If a client requires a realm name, the client sends a DHCPv6 Option
Request option (ORO) specifying the Kerberos Default Realm Name
Option. The DHCPv6 server responds with a Reply message containing a
Kerberos Default Realm Name Option.
If a client requires configuration parameters for a KDC, the client
sends a DHCPv6 ORO specifying the Kerberos KDC Option. The client
MAY include a Kerberos Principal Name Option. The client MAY include
a Kerberos Realm Name Option.
The DHCPv6 server replies with one or more sets of configuration
parameters for a Kerberos KDC. If the client has specified either a
Kerberos Principal Name Option or a Kerberos Realm Name Option, then
the DHCPv6 server MAY use those parameters to select specific sets of
configuration parameters.
Where the server replies with more than one set of configuration
paramers, the usage of priority and weight fields by the client MUST
follow the specification for DNS SRV [RFC2782].
The client MAY include other options with data values as hints to the
DHCPv6 server about parameter values the client would like to have
returned; this is specified in section 18.1.5 of RFC 3315 [RFC3315].
4.1. KDC discovery for a client
When a client implements both the DNS method defined by section
7.2.3.2 of [RFC4120] and the DHCP method defined by this document,
the choice of method is determined by local policy. The
administrator of the realm usually defines the method as part of the
configuration of the client before the client is installed.
When no criteria have been specified and the client could get the
Kerberos information from either the DNS server or the DHCPv6 server,
then the information from DNS SHOULD be preferred.
Sakane & Ishiyama Expires March 17, 2013 [Page 9]
Internet-Draft Kerberos Options for DHCPv6 September 2012
5. IANA Considerations
IANA is requested to assign four option codes from the "DHCPv6
Options Codes" registry for the following:
OPTION_KRB_PRINCIPAL_NAME
OPTION_KRB_REALM_NAME
OPTION_KRB_DEFAULT_REALM_NAME
OPTION_KRB_KDC
IANA is requested to create a sub-registry of Kerberos Message
Transport Type, under the Kerberos Parameters Registry. The initial
entries are described in section 3.4.
The assignment of future entries is by "IETF Review" policy as
described in BCP 26 [RFC5226]. The RFC specifies the symbolic name
of such entries which are assigned numeric codes by IANA once
publication is approved.
Sakane & Ishiyama Expires March 17, 2013 [Page 10]
Internet-Draft Kerberos Options for DHCPv6 September 2012
6. Security Considerations
The security considerations in RFC 3315 [RFC3315] apply.
DHCPv6 messages can be modified in transit. If an adversary modifies
the response from a DHCPv6 server or injects its own response, a
client may be led into contacting a malicious KDC. Both cases are
categorized as a Denial of Service (DoS) attack. However, a
malicious KDC does not know the shared key and so is unable to
proceed any further with the exchange. If a client receives a
response from such a KDC, the client can use the shared key to detect
that the message originates from a malicious KDC.
A shared, unconfigured workstation may obtain its KDC information,
and default realm, via DHCPv6. Such a workstation may not have a
host or other service key, and thus be unable to validate the Ticket-
Granting Ticket issued by the KDC. A modified DHCPv6 response would
then result in the workstation talking to a malicious KDC and be
unable to detect that has happened. This in turn could allow access
by unauthorized users.
To minimize potential vulnerabilities, a client SHOULD use DHCPv6
authentication as defined in section 21 of RFC 3315 [RFC3315].
Kerberos information may be manually configured into the client
before requesting information from DHCPv6. Manual configuration of
the device SHOULD be preferred to configuration via the DHCPv6
server.
Sakane & Ishiyama Expires March 17, 2013 [Page 11]
Internet-Draft Kerberos Options for DHCPv6 September 2012
7. Acknowledgments
The authors are very grateful to Nobuo Okabe and Shigeya Suzuki.
They contributed the explanation as to why DNS is inappropriate for
some industry networks. Ted Lemon made many suggestions to improve
DHCP aspects of this specification. Ken'ichi Kamada and Yukiyo
Akisada contributed to the initial work on this document. Tom Petch
helped to improve the readability of this document. The authors also
thank Jeffrey Hutzelman, Kazunori Miyazawa, Kensuke Hosoya, Nicolas
Williams, Nobumichi Ozoe, Sam Hartman, and Stephen Farrell. They
made valuable comments and suggestions.
Sakane & Ishiyama Expires March 17, 2013 [Page 12]
Internet-Draft Kerberos Options for DHCPv6 September 2012
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005.
[RFC5021] Josefsson, S., "Extended Kerberos Version 5 Key
Distribution Center (KDC) Exchanges over TCP", RFC 5021,
August 2007.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
8.2. Informative References
[PCARCH] CableLabs, "PacketCable 1.0 Architecture Framework
Technical Report", December 1999, <http://
www.packetcable.com/downloads/specs/
pkt-tr-arch-v01-991201.pdf>.
[RFC3634] Luehrs, K., Woundy, R., Bevilacqua, J., and N. Davoust,
"Key Distribution Center (KDC) Server Address Sub-option
for the Dynamic Host Configuration Protocol (DHCP)
CableLabs Client Configuration (CCC) Option", RFC 3634,
December 2003.
[RFC6251] Josefsson, S., "Using Kerberos Version 5 over the
Transport Layer Security (TLS) Protocol", RFC 6251,
May 2011.
Sakane & Ishiyama Expires March 17, 2013 [Page 13]
Internet-Draft Kerberos Options for DHCPv6 September 2012
Appendix A. An example of the operation of the client
When no criteria have been specified and the client could get the
Kerberos information from either the DNS server or the DHCPv6 server,
then the information from DNS should be preferred. The following is
an informational guide for the client in such an environment.
Sakane & Ishiyama Expires March 17, 2013 [Page 14]
Internet-Draft Kerberos Options for DHCPv6 September 2012
No Resp. or
+------------+ DNS Info. +-----------+ No Resp.
Start --> | Ask DHCP(1)| ---------> | Ask DNS(3)| ------>
+------------+ +-----------+ Terminate(4)
/ \ \
Only KRB / \ DNS and \ KRB Info.
Info. / \ KRB Info. \
/ \ \
| | |
| V |
V No Ans. +-----------+ KRB Info. V
Use Info. <-------- | Ask DNS(6)| ---------> Use Info.
from DHCP +-----------+ from DNS
(2), (7) (5), (8)
Abbreviations:
Resp.: Response
Info.: Information
KRB : Kerberos
1) Initially, the client requests both DNS and Kerberos information
from the DHCPv6 server.
2) If the DHCPv6 server replies with Kerberos information and not
with DNS information, then the client uses that information.
3) If the DHCPv6 server does not reply or replies with only DNS
information, then the client requests Kerberos information from
the DNS server.
4) If the client gets no response or no Kerberos information from the
DNS server, then the client terminates the process.
5) If the client gets Kerberos information from the DNS server, then
the client uses that information.
6) If, as the result of (1), the DHCPv6 server replies with both DNS
and Kerberos information, then the client requests Kerberos
information from the DNS server.
7) If the client gets no response from the DNS server, then the
client uses the Kerberos information from the DHCPv6 server.
8) If, as the result of (6), the DNS server replies with Kerberos
information, then the client uses the information from the DNS
server and not that from the DHCPv6 server.
Sakane & Ishiyama Expires March 17, 2013 [Page 15]
Internet-Draft Kerberos Options for DHCPv6 September 2012
Authors' Addresses
Shoichi Sakane
Cisco Systems
9-7-1 Akasaka
Minato-ku, Tokyo 107-6227
Japan
Email: ssakane@cisco.com
Masahiro Ishiyama
Toshiba Corporation
1, komukai-toshiba-cho, Saiwai-ku,
Kawasaki, Kanagawa 212-8582
Japan
Email: masahiro.ishiyama@toshiba.co.jp
Sakane & Ishiyama Expires March 17, 2013 [Page 16]
