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rfc:rfc3594

Network Working Group P. Duffy Request for Comments: 3594 Cisco Systems Category: Standards Track September 2003

          PacketCable Security Ticket Control Sub-Option
     for the DHCP CableLabs Client Configuration (CCC) Option

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

 This document defines a new sub-option for the DHCP CableLabs Client
 Configuration (CCC) Option.  This new sub-option will be used to
 direct CableLabs Client Devices (CCDs) to invalidate security tickets
 stored in CCD non volatile memory (i.e., locally persisted security
 tickets).

1. 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 BCP 14, RFC 2119 [2].

2. Terminology

 Definitions of terms/acronyms used throughout this document:
 CCC - CableLabs Client Configuration option, described in [1].
 CCD - CableLabs Client Device.  A PacketCable MTA is an example of a
       CCD.
 STC - Security Ticket Control.  The CCC sub-option described in this
       document.

Duffy Standards Track [Page 1] RFC 3594 Security Ticket Control September 2003

 MTA - Media Terminal Adapter.  The CCD specific to the PacketCable
       architecture.
 PacketCable - multimedia architecture developed by CableLabs.  See
       [8] for full details.

3. Introduction

 The CableLabs Client Configuration Option [1] defines several
 sub-options used to configure devices deployed into CableLabs
 architectures.  These architectures implement the PacketCable
 Security Specification [4] (based on Kerberos V5 [5]), to support CCD
 authentication and establishment of security associations between
 CCDs and application servers.
 CCDs are permitted to retain security tickets in local persistent
 storage.  Thus a power-cycled CCD is enabled to avoid expensive
 ticket acquisition for locally persisted, non-expired tickets.  This
 feature greatly reduces the security overhead of a deployment.
 This sub-option allows the service provider to control the lifetime
 of tickets persisted locally on a CCD.  The service provider requires
 this capability to support operational functions such as forcing re-
 establishment of security associations, remote testing, and remote
 diagnostic of CCDs.
 It should be noted that, although based on the Kerberos V5 RFC [5],
 the PacketCable Security Specification is not a strict implementation
 of this RFC.  See [4] for details of the PacketCable Security
 Specification.

4. Security Ticket Control Sub-option

 This sub-option defines a Ticket Control Mask (TCM) that instructs
 the CCD to validate/invalidate specific application server tickets.
 The sub-option is encoded as follows:
  Code   Len      TCM
 +-----+-----+-----+-----+
 |  9  |  2  | m1  | m2  |
 +-----+-----+-----+-----+
 The length MUST be 2.  The TCM field is encoded as an unsigned 16 bit
 quantity per network byte order.  Each bit of the TCM is assigned to
 a specific server or server group.  A bit value of 0 means the CCD
 MUST apply normal invalidation rules (defined in [4]) to the locally

Duffy Standards Track [Page 2] RFC 3594 Security Ticket Control September 2003

 persisted ticket for the server/server group. A bit value of 1 means
 the CCD MUST immediately invalidate the locally persisted ticket for
 the server/server group.
 Bit #0 is the least significant bit of the field.  The bit positions
 are assigned as follows:
    Bit #0 - the PacketCable Provisioning Server used by the CCD.
    Bit #1 - the group of all PacketCable Call Management Servers used
    by the CCD.
    Bit #2 - #15.  Reserved and MUST be set to 0.
 If a CCD does not locally store tickets, it MUST ignore this
 sub-option.  Bit values not known to the CCD MUST be ignored.

5. IANA Considerations

 IANA has assigned a sub-option code to this sub-option from the
 "CableLabs Client Configuration" sub-option number space (maintained
 within the BOOTP-DHCP Parameters Registry).
 IANA has also set-up a new registry and will maintain a new number
 space of "CableLabs Client Configuration Option Ticket Control Mask
 Bit Definitions", located in the BOOTP-DHCP Parameters Registry.  The
 initial bit definitions are described in section 4 of this document.
 IANA will register future bit mask definitions via an "IETF
 Consensus" approval policy as described in RFC 2434 [3].

6. Security Considerations

 Potential DHCP protocol attack exposure is discussed in section 7 of
 the DHCP protocol specification [6] and in Authentication for DHCP
 Messages [7].  Additional CCC attack exposure is discussed in [1].
 The STC sub-option could be used to disrupt a CableLabs architecture
 deployment.  In the specific case of PacketCable [8], a deployment
 could be disrupted if a large number of MTAs are reset/power cycled,
 initiate their provisioning flow [9], and are instructed by a
 malicious DHCP server to invalidate all security tickets.  This could
 lead to a Denial of Service (DoS) condition as this large set of MTAs
 simultaneously attempt to authenticate and obtain tickets from the
 security infrastructure.
 However, the scenario described above is unlikely to occur. Within
 the cable delivery architecture required by the various CableLabs
 projects, the DHCP client is connected to a network through a cable

Duffy Standards Track [Page 3] RFC 3594 Security Ticket Control September 2003

 modem and the CMTS (head-end router).  The CMTS is explicitly
 configured with a set of valid DHCP server addresses to which DHCP
 requests are forwarded.  Further, a correctly configured CMTS will
 only allow DHCP downstream traffic from specific DHCP server
 addresses.
 It should be noted that the downstream filtering of DHCP packets will
 not prevent spoofed DHCP servers behind the CMTS, but the network
 infrastructure behind the CMTS is assumed to be closely controlled by
 the service provider.

7. Intellectual Property Statement

 The IETF takes no position regarding the validity or scope of any
 intellectual property or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; neither does it represent that it
 has made any effort to identify any such rights.  Information on the
 IETF's procedures with respect to rights in standards-track and
 standards-related documentation can be found in BCP-11.  Copies of
 claims of rights made available for publication and any assurances of
 licenses to be made available, or the result of an attempt made to
 obtain a general license or permission for the use of such
 proprietary rights by implementors or users of this specification can
 be obtained from the IETF Secretariat.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights which may cover technology that may be required to practice
 this standard.  Please address the information to the IETF Executive
 Director.

Duffy Standards Track [Page 4] RFC 3594 Security Ticket Control September 2003

8. References

8.1. Normative

 [1] Beser, B. and P. Duffy, "DHCP Option for CableLabs Client
     Configuration", RFC 3495, March 2003.
 [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
     Levels", BCP 14, RFC 2119, March 1997.
 [3] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
     Considerations Section in RFCs", RFC 2434, October 1998.
 [4] "PacketCable Security Specification", PKT-SP-SEC-I09-030728,
     http://www.packetcable.com/downloads/specs/
     PKT-SP-SEC-I09-030728.pdf

8.2. Informative

 [5] Kohl, J. and C. Neuman, "The Kerberos Network Authentication
     Service (V5)", RFC 1510, September 1993.
 [6] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March
     1997.
 [7] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages", RFC
     3118, June 2001
 [8] "PacketCable 1.0 Architecture Framework Technical Report",
     PKT-TR-ARCH-V01-991201,
     http://www.packetcable.com/downloads/specs/
     pkt-tr-arch-v01-991201.pdf
 [9] "PacketCable MTA Device Provisioning Specification",
     PKT-SP-PROV-I07-030728,
     http://www.packetcable.com/downloads/specs/
     PKT-SP-PROV-I07-030728.pdf

Duffy Standards Track [Page 5] RFC 3594 Security Ticket Control September 2003

9. Acknowledgments

 The author would like to acknowledge the effort of all those who
 contributed to the development of the PacketCable Provisioning
 specifications:
 Sumanth Channabasappa (Alopa Networks); Angela Lyda, Rick Morris,
 Rodney Osborne (Arris Interactive); Steven Bellovin and Chris
 Melle (AT&T); Eugene Nechamkin (Broadcom); John Berg, Maria
 Stachelek, Matt Osman, Venkatesh Sunkad (CableLabs); Klaus
 Hermanns, Azita Kia, Michael Thomas, Paul Duffy (Cisco); Deepak
 Patil (Com21); Jeff Ollis, Rick Vetter (General
 Instrument/Motorola); Roger Loots, David Walters (Lucent); Peter
 Bates (Telcordia); Patrick Meehan (Tellabs); Satish Kumar, Itay
 Sherman, Roy Spitzer (Telogy/TI), Aviv Goren (Terayon);
 Prithivraj Narayanan (Wipro), and Burcak Beser (Juniper
 Networks).

10. Author's Address

 Paul Duffy
 Cisco Systems
 1414 Massachusetts Avenue
 Boxborough, MA 01719
 EMail: paduffy@cisco.com

Duffy Standards Track [Page 6] RFC 3594 Security Ticket Control September 2003

11. Full Copyright Statement

 Copyright (C) The Internet Society (2003).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assignees.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Duffy Standards Track [Page 7]

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