draft-ietf-dhc-server-override-04.txt   draft-ietf-dhc-server-override-05.txt 
Network Working Group R. Johnson Network Working Group R. Johnson
Internet-Draft J. Jumarasamy Internet-Draft J. Jumarasamy
Expires: April 25, 2007 K. Kinnear Expires: May 19, 2008 K. Kinnear
M. Stapp M. Stapp
Cisco Systems, Inc. Cisco Systems, Inc.
October 22, 2006 November 16, 2007
DHCP Server Identifier Override Suboption DHCP Server Identifier Override Suboption
draft-ietf-dhc-server-override-04.txt draft-ietf-dhc-server-override-05.txt
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on April 25, 2007. This Internet-Draft will expire on May 19, 2008.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The IETF Trust (2007).
Abstract Abstract
This memo defines a new suboption of the DHCP relay information This memo defines a new suboption of the DHCP relay information
option which allows the DHCP relay to specify a new value for the option which allows the DHCP relay to specify a new value for the
Server Identifier option, which is inserted by the DHCP Server. This Server Identifier option, which is inserted by the DHCP Server. This
allows the DHCP relay to act as the actual DHCP server such that allows the DHCP relay to act as the actual DHCP server such that
RENEW DHCPREQUESTs will come to the relay instead of going to the RENEW DHCPREQUESTs will come to the relay instead of going to the
server directly. This gives the relay the opportunity to include the server directly. This gives the relay the opportunity to include the
Relay Agent option with appropriate suboptions even on DHCP RENEW Relay Agent option with appropriate suboptions even on DHCP RENEW
messages. messages.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Server Identifier Override Suboption Definition . . . . . . 5 3. Server Identifier Override Suboption Definition . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . 7 4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . 8 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Intellectual Property Rights and Copyright . . . . . . . . . 9 6. Intellectual Property Rights and Copyright . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 10 7.1. Normative References . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . 11 7.2. Informative References . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . . . . 12
1. Introduction 1. Introduction
There are many situations where the DHCP relay is involved and can There are many situations where the DHCP relay is involved and can
insert a relay agent option with appropriate suboptions easily into insert a relay agent option [3] with appropriate suboptions easily
DHCP DISCOVER messages. Once the lease has been granted, however, into DHCP DISCOVER messages. Once the lease has been granted,
future DHCP RENEWAL messages are sent directly to the DHCP Server as however, future DHCP RENEWAL messages are sent directly to the DHCP
specified in the Server Identifier option. This means that the relay Server as specified in the Server Identifier option. This means that
may not see the DHCP RENEWAL messages (depending upon network the relay may not see the DHCP RENEWAL messages (depending upon
topology) and thus can not provide the same relay agent option network topology) and thus can not provide the same relay agent
information in the RENEWAL messages. option information in the RENEWAL messages.
This new DHCP relay agent suboption, Server Identifier override, This new DHCP relay agent suboption, Server Identifier override,
allows the relay to tell the DHCP server what value to place into the allows the relay to tell the DHCP server what value to place into the
Server Identifier option. Using this, the relay agent can force Server Identifier option [5]. Using this, the relay agent can force
RENEWAL messages to come to it instead of the server. The relay may RENEWAL messages to come to it instead of the server. The relay may
then insert the relay agent option with appropriate suboptions and then insert the relay agent option with appropriate suboptions and
relay the DHCPREQUEST to the actual server. In this fashion the DHCP relay the DHCPREQUEST to the actual server. In this fashion the DHCP
server will be provided with the same relay agent information upon server will be provided with the same relay agent information upon
renewals (such as Circuit-ID, Remote-ID, Device Class, etc.) as was renewals (such as Circuit-ID, Remote-ID, Device Class, etc.) as was
provided in the initial DISCOVER message. In effect, this makes a provided in the initial DISCOVER message. In effect, this makes a
RENEWAL into a REBINDING. RENEWAL into a REBINDING.
This new suboption could also be used by the DHCP relay in order to 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. 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 This has the advantage that the relay can more easily keep up-to-date
information about leases granted, etc. information about leases granted, etc.
In short, this new suboption allows the DHCPv4 relay to function in In short, this new suboption allows the DHCPv4 relay to function in
the same fashion as the DHCPv6 relay currently does. the same fashion as the DHCPv6 relay [7] currently does.
2. Conventions 2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY" and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY" and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1]. document are to be interpreted as described in [1].
3. Server Identifier Override Suboption Definition 3. Server Identifier Override Suboption Definition
The format of the suboption is: The format of the suboption is:
Code Len Overriding Server Identifier address Code Len Overriding Server Identifier address
+-----+-----+-----+-----+-----+-----+ +-----+-----+-----+-----+-----+-----+
| TBD | n | a1 | a2 | a3 | a4 | | TBD | n | a1 | a2 | a3 | a4 |
+-----+-----+-----+-----+-----+-----+ +-----+-----+-----+-----+-----+-----+
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Server Identifier Option specify the same address, then the Server Server Identifier Option specify the same address, then the Server
should accept the DHCPREQUEST packet for processing, regardless of should accept the DHCPREQUEST packet for processing, regardless of
whether or not the Server Identifier Option matchs a DHCP Server whether or not the Server Identifier Option matchs a DHCP Server
interface. interface.
The DHCP Relay should fill in the giaddr field when relaying the The DHCP Relay should fill in the giaddr field when relaying the
packet just as it normally would do. packet just as it normally would do.
In a situation where the DHCP Relay is configured to forward packets In a situation where the DHCP Relay is configured to forward packets
to more than one server, the DHCP Relay should forward all DHCP to more than one server, the DHCP Relay should forward all DHCP
packets all servers. This applies to DHCP RENEW packets as well. packets to all servers. This applies to DHCP RENEW packets as well.
The intent is that the DHCP Relay should not need to maintain state The intent is that the DHCP Relay should not need to maintain state
information about the DHCP lease. information about the DHCP lease.
DHCP Relays using this suboption SHOULD also implement and use the DHCP Relays using this suboption SHOULD also implement and use the
DHCPv4 Relay Agent Flags Suboption [7] in order to specify whether DHCPv4 Relay Agent Flags Suboption [4] in order to specify whether
the DHCP Relay received the original packet as a broadcast or the DHCP Relay received the original packet as a broadcast or
unicast. The DHCP Server receiving a packet containing the Server unicast. The DHCP Server receiving a packet containing the Server
Identifier Override Suboption may use this additional information in Identifier Override Suboption may use this additional information in
processing the packet. processing the packet.
Note that if the DHCP Relay becomes inaccessible by the DHCP Client Note that if the DHCP Relay becomes inaccessible by the DHCP Client
or loses network access to the DHCP Server, further DHCP RENEW or loses network access to the DHCP Server, further DHCP RENEW
packets from the DHCP Client may not be properly processed and the packets from the DHCP Client may not be properly processed and the
DHCP Client's lease may time out. DHCP Client's lease may time out.
4. Security Considerations 4. Security Considerations
Message authentication in DHCP for intradomain use where the out-of- Message authentication in DHCP for intradomain use where the out-of-
band exchange of a shared secret is feasible is defined in [3]. band exchange of a shared secret is feasible is defined in [6].
Potential exposures to attack are discussed in section 7 of the DHCP Potential exposures to attack are discussed in section 7 of the DHCP
protocol specification in [2]. protocol specification in [2].
The DHCP Relay Agent option depends on a trusted relationship between 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 the DHCP relay agent and the server, as described in section 5 of RFC
3046. While the introduction of fraudulent relay-agent options can 3046. While the introduction of fraudulent relay-agent options can
be prevented by a perimeter defense that blocks these options unless be prevented by a perimeter defense that blocks these options unless
the relay agent is trusted, a deeper defense using the authentication the relay agent is trusted, a deeper defense using the authentication
option for relay agent options [4] SHOULD be deployed as well. option for relay agent options [8] SHOULD be deployed as well.
If a rogue DHCP relay were inserted between the client and the If a rogue DHCP relay were inserted between the client and the
server, it could redirect clients to it using this suboption. This server, it could redirect clients to it using this suboption. This
would allow such a system to later deny RENEW DHCPREQUEST and thus would allow such a system to later deny RENEW DHCPREQUEST and thus
force clients to discontinue use of their allocated address. This force clients to discontinue use of their allocated address. It
interception, however, would need to be done during the initial could also allow the rogue relay to change, insert, or delete DHCP
DISCOVER and OFFER phase, since the suboption value SHOULD be ignored options in DHCPACK messages and extend leases beyond what the server
by the server during RENEWAL state. Either DHCP Authentication [3] has allowed. This interception, however, would need to be done
or DHCP Relay Agent option authentication [4] would address this during the initial DISCOVER and OFFER phase, since the suboption
case. value SHOULD be ignored by the server during RENEWAL state. DHCP
Authentication [6] and/or DHCP Relay Agent option authentication [8]
would address this case. (Note that, as is always the case, lack of
DHCP Authentication would allow a rogue DHCP relay to change the
Server-ID option in the DHCPOFFER and DHCPACK packets without
detection. This threat is not new to the Server-ID-Override
suboption.)
This draft does not add any new vulnerabilities that were not already
present, except in the case where DHCP authentication is already in
place and DHCP clients require its use. It is suggested that DHCP
Authentication and DHCP Relay Agent Option Authentication SHOULD be
deployed when this option is used, or protection should be provided
against the insertion of rogue DHCP relays and server.
This relay sub-option is not intended, by itself, to provide any
additional security benefits.
5. IANA Considerations 5. IANA Considerations
IANA is requested to assign a suboption number for the Server IANA is requested to assign a suboption number for the Server
Identifier Override Suboption from the DHCP Relay Agent Information Identifier Override Suboption from the DHCP Relay Agent Information
Option [3] suboption number space. None. Option [3] suboption number space.
6. Intellectual Property Rights and Copyright 6. Intellectual Property Rights and Copyright
The IETF has been notified of intellectual property rights claimed in The IETF has been notified of intellectual property rights claimed in
regard to some or all of the specification contained in this regard to some or all of the specification contained in this
document. For more information consult the online list of claimed document. For more information consult the online list of claimed
rights. rights.
Copyright (C) The Internet Society (2006). 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.
7. References 7. References
7.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, BCP 14, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[2] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, [2] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997. March 1997.
[3] Droms, R., "Authentication for DHCP Messages", RFC 3118, [3] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046,
June 2001. January 2001.
[4] Stapp, M., "The Authentication Suboption for the DHCP Relay [4] Kinnear, K., Normoyle, M., and M. Stapp, "The Dynamic Host
Agent Option", RFC 4030, March 2005. Configuration Protocol Version 4 (DHCPv4) Relay Agent Flags
Suboption", RFC 5010, September 2007.
[5] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA 7.2. Informative References
Considerations Section in RFCs", RFC 2434, October 1998.
[6] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046, [5] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
November 2004. Extensions", RFC 2132, March 1997.
[7] Kinnear, K., "DHCPv4 Relay Agent Flags Suboption", [6] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages",
draft-ietf-dhc-relay-agent-flags-00.txt (work in progress), RFC 3118, June 2001.
June 2006.
[7] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M.
Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 3315, July 2003.
[8] Stapp, M. and T. Lemon, "The Authentication Suboption for the
Dynamic Host Configuration Protocol (DHCP) Relay Agent Option",
RFC 4030, March 2005.
Authors' Addresses Authors' Addresses
Richard A. Johnson Richard A. Johnson
Cisco Systems, Inc. Cisco Systems, Inc.
170 W. Tasman Dr. 170 W. Tasman Dr.
San Jose, CA 95134 San Jose, CA 95134
US US
Phone: +1 408 526 4000 Phone: +1 408 526 4000
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Mark Stapp Mark Stapp
Cisco Systems, Inc. Cisco Systems, Inc.
170 W. Tasman Dr. 170 W. Tasman Dr.
San Jose, CA 95134 San Jose, CA 95134
US US
Phone: +1 408 526 4000 Phone: +1 408 526 4000
Email: mjs@cisco.com Email: mjs@cisco.com
Intellectual Property Statement Full Copyright Statement
Copyright (C) The IETF Trust (2007).
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, THE IETF TRUST 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.
Intellectual Property
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79. found in BCP 78 and BCP 79.
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such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Disclaimer of Validity
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.
Copyright Statement
Copyright (C) The Internet Society (2006). 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 Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is provided by the IETF
Internet Society. Administrative Support Activity (IASA).
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