Internet Engineering Task Force                          Richard
Network Working Group                                         R. Johnson
Internet Draft                                               Kim Kinnear
Expiration: March
Internet-Draft                                             J. Jumarasamy
Expires: December 31, 2005                                        Mark                                    K. Kinnear
                                                                M. Stapp
File: draft-ietf-dhc-server-override-01.txt               Jay Kumarasamy
                                                     Cisco Systems, Inc.
                                                           June 29, 2005

                   DHCP Server-ID Override Suboption
                <draft-ietf-dhc-server-override-01.txt>

                           September 27, 2004
                 draft-ietf-dhc-server-override-02.txt

Status of this Memo

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Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved. (2005).

Abstract

   This memo defines a new suboption of the DHCP relay information
   option [6] which allows the DHCP relay to specify a new value for the
   Server-ID option, which is inserted by the DHCP Server.  In some
   cases it is convenient for the DHCP relay to act as the actual DHCP
   server such that DHCP RENEWAL requests will come to the relay instead
   of going to the server directly.  This gives the relay the
   opportunity to include the Relay Agent option with appropriate
   suboptions even on RENEWAL messages.

   This new relay agent suboption allows the relay to tell the DHCP
   server what value to use in the Server-ID option [3].  If this
   suboption is not present, the server should build the

Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.   Server-ID
   option in the normal fashion.

1.0 Override Suboption Definition  . . . . . . . . . . . 4
   3.   Security Considerations  . . . . . . . . . . . . . . . . . . . 5
   4.   IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 6
   5.   Intellectual Property Rights and Copyright . . . . . . . . . . 7
   6.   References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 8
        Intellectual Property and Copyright Statements . . . . . . . . 9

1.  Introduction

   There are many situations where the DHCP relay is involved and can
   insert a relay agent option with appropriate suboptions easily into
   DHCP DISCOVER messages.  Once the lease has been granted, however,
   future DHCP RENEWAL messages are sent directly to the DHCP Server as
   specified in the Server-ID option.  This means that the relay may not
   see the DHCP RENEWAL messages (depending upon network topology) and
   thus can not provide the same relay agent option information in the
   RENEWAL messages.

   This new DHCP relay agent suboption, Server-ID override, allows the
   relay to tell the DHCP server what value to place into the Server-ID
   option.  Using this, the relay agent can force RENEWAL messages to
   come to it instead of the server.  The relay may then insert the
   relay agent option with appropriate suboptions and relay the request
   to the actual server.  In this fashion the DHCP server will be
   provided with the same relay agent information upon renewals (such as
   Circuit-ID, Remote-ID, Device Class, etc.) as was provided in the
   initial DISCOVER message.  In effect, this makes a RENEWAL into a
   REBINDING.

   This new suboption could also be used by the DHCP relay in order to
   allow the relay to appear as the actual DHCP server to the client.
   This has the advantage that the relay can more easily keep up-to-date
   information about leases granted, etc.

   In short, this new suboption allows the DHCPv4 relay to function in
   the same fashion as the DHCPv6 relay currently does.

1.1 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 [1].

2.0

2.  Server-ID Override Suboption Definition

   The format of the suboption is:

   Code   Len    Overridden    Overriding Server-ID address
   +-----+-----+-----+-----+-----+-----+
   | TBD |  n  | a1  | a2  | a3  | a4  |
   +-----+-----+-----+-----+-----+-----+

                                 Figure 1

   The option length (n) is 4.  The octets "a1" through "a4" specify the
   value which SHOULD be inserted into the Server-ID option by the DHCP
   Server upon reply.

   DHCP Servers SHOULD use this value, if present, as the value to
   insert into the Server-ID option whenever responding to a DHCP
   Client.

   When servicing a DHCP REQUEST packet the DHCP Server would normally
   look at the Server-ID option for verification that the address
   specified there is one of the addresses associated with the DHCP
   Server, silently ignoring the REQUEST if it does not match a
   configured DHCP Server interface address.  If the REQUEST packet
   contains a Server-ID Override Suboption, however, comparison should
   be made between this suboption and the Server-ID option.  If both of
   the Server-ID Override Suboption and the Server-ID Option specify the
   same address, then the Server should accept the REQUEST packet for
   processing, regardless of whether or not the Server-ID Option matchs
   a DHCP Server interface.

3.0 IANA Considerations

   None.

4.0 Acknowledgements

   This document is the result of work done within Cisco Systems.
   Thanks to Jay Kumarasamy, Kim Kinnear, and Mark Stapp for their work
   on this suboption definition and the other related work for which
   this is necessary.

5.0

3.  Security Considerations

   Message authentication in DHCP for intradomain use where the out-of-
   band exchange of a shared secret is feasible is defined in RFC 3118
   [5]. [3].
   Potential exposures to attack are discussed in section 7 of the DHCP
   protocol specification in RFC 2131 [2].

   The DHCP Relay Agent option depends on a trusted relationship between
   the DHCP relay agent and the server, as described in section 5 of RFC
   3046.  While the introduction of fraudulent relay-agent options can
   be prevented by a perimeter defense that blocks these options unless
   the relay agent is trusted, a deeper defense using the authentication
   option for relay agent options [4] SHOULD be deployed as well.

   If a rogue DHCP relay were inserted between the client and the
   server, it could redirect clients to it using this suboption.  This
   would allow such a system to later deny renew requests and thus force
   clients to discontinue use of their allocated address.  This
   interception, however, would need to be done during the initial
   DISCOVER and OFFER phase, since the suboption value SHOULD be ignored
   by the server during RENEWAL state.  Either DHCP Authentication [5] [3]
   or DHCP Relay Agent option authentication [4] would address this
   case.

6.0

4.  IANA Considerations

   None.

5.  Intellectual Property Rights and Copyright

   The IETF has been notified of intellectual property rights claimed in
   regard to some or all of the specification contained in this
   document.  For more information consult the online list of claimed
   rights.

   Copyright (C) The Internet Society (2004).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights."

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM 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.

6.  References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", RFC 2119, BCP 14, March 1997.

   [2]  Droms, R. R., "Dynamic Host Configuration Protocol", RFC 2131,
        March 1997.

   [3] Alexander, S. and  Droms, R., "DHCP Options and BOOTP Vendor
             Extensions", "Authentication for DHCP Messages", RFC 2132, March 1997. 3118,
        June 2001.

   [4]  Stapp, M. M., "The Authentication Suboption for the DHCP Relay
        Agent Option", draft-ietf-dhc-auth-suboption-00.txt,
       June 23, 2002 RFC 4030, March 2005.

   [5] Droms, R. "Authentication  Narten, T. and H. Alvestrand, "Guidelines for DHCP Messages", Writing an IANA
        Considerations Section in RFCs", RFC 3118,
       June 2001 2434, October 1998.

   [6]  Patrick, M., "DHCP Relay Agent Information Option", RFC 3046, January 2001

Author Information: 3096,
        November 2004.

Authors' Addresses

   Richard A. Johnson
   Cisco Systems, Inc.
   170 W. Tasman Dr.
   San Jose, CA  95134
   US

   Phone: +1 408 526 4000
   Email: raj@cisco.com

   Jay Kumarasamy
   Cisco Systems Systems, Inc.
   170 W. Tasman Dr.
   San Jose, CA  95134
   US

   Phone: (408) 526-4000

   EMail: +1 408 526 4000
   Email: jayk@cisco.com
          raj@cisco.com

   Kim Kinnear
   Cisco Systems, Inc.
   170 W. Tasman Dr.
   San Jose, CA  95134
   US

   Phone: +1 408 526 4000
   Email: kkinnear@cisco.com

   Mark Stapp
   Cisco Systems
   250 Apollo Drive
   Chelmsford, MA  01824 Systems, Inc.
   170 W. Tasman Dr.
   San Jose, CA  95134
   US

   Phone: (978) 244-8000

   EMail: kkinnear@cisco.com +1 408 526 4000
   Email: mjs@cisco.com

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   ENGINEERING TASK FORCE DISCLAIM 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.

Copyright Statement

   Copyright (C) The Internet Society (2005).  This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.

Acknowledgment

   Funding for the RFC Editor function is currently provided by the
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