draft-ietf-dhc-relay-agent-flags-03.txt   rfc5010.txt 
DHC K. Kinnear Network Working Group K. Kinnear
Internet-Draft M. Normoyle Request for Comments: 5010 M. Normoyle
Intended status: Standards Track M. Stapp Category: Standards Track M. Stapp
Expires: October 25, 2007 Cisco Systems, Inc. Cisco Systems, Inc.
April 23, 2007 September 2007
DHCPv4 Relay Agent Flags Suboption
draft-ietf-dhc-relay-agent-flags-03.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
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
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
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The list of current Internet-Drafts can be accessed at
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The list of Internet-Draft Shadow Directories can be accessed at
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This Internet-Draft will expire on October 25, 2007. The Dynamic Host Configuration Protocol Version 4 (DHCPv4)
Relay Agent Flags Suboption
Copyright Notice Status of This Memo
Copyright (C) The IETF Trust (2007). 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.
Abstract Abstract
This memo defines a new suboption of the DHCP relay agent information This memo defines a new suboption of the Dynamic Host Configuration
option that allows the DHCP relay to specify flags for the forwarded Protocol (DHCP) relay agent information option that allows the DHCP
packet. One flag is defined to indicate whether the DHCP relay relay to specify flags for the forwarded packet. One flag is defined
received the packet via a unicast or broadcast packet. This to indicate whether the DHCP relay received the packet via a unicast
information may be used by the DHCP server to better serve clients or broadcast packet. This information may be used by the DHCP server
based on whether their request was originally broadcast or unicast. to better serve clients based on whether their request was originally
broadcast or unicast.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Terminology . . . . . . . . . . . . . . . . . . . 3 2. Requirements Terminology . . . . . . . . . . . . . . . . . . . 2
3. The Flags Suboption . . . . . . . . . . . . . . . . . . . . . . 4 3. The Flags Suboption . . . . . . . . . . . . . . . . . . . . . . 3
4. DHCP Relay Agent Behavior . . . . . . . . . . . . . . . . . . . 4 4. DHCP Relay Agent Behavior . . . . . . . . . . . . . . . . . . . 3
5. DHCP Server Behavior . . . . . . . . . . . . . . . . . . . . . 5 5. DHCP Server Behavior . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
9.1. Normative References . . . . . . . . . . . . . . . . . . . 6 9.1. Normative References . . . . . . . . . . . . . . . . . . . 5
9.2. Informative References . . . . . . . . . . . . . . . . . . 6 9.2. Informative References . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 8
1. Introduction 1. Introduction
Any time a client's DHCP packet is broadcast, a local DHCP relay will Any time a client's DHCP packet is broadcast, a local DHCP relay will
process its request and forward it on to the DHCP server. When the process its request and forward it on to the DHCP server. When the
DHCP relay performs this function, it can be configured to use the DHCP relay performs this function, it can be configured to use the
DHCP relay agent information option to forward additional information DHCP relay agent information option to forward additional information
to the DHCP server, which the server may then use to alter its to the DHCP server, which the server may then use to alter its
processing algorithms. Once the lease has been granted, however, processing algorithms. Once the lease has been granted, however,
future DHCP DHCPREQUEST/RENEWAL messages are unicast directly to the future DHCP DHCPREQUEST/RENEWAL messages are unicast directly to the
DHCP Server. [RFC2131] [RFC2132] [RFC3046] DHCP Server [RFC2131] [RFC2132] [RFC3046].
In general, DHCP servers may also make subtle (and sometimes not so In general, DHCP servers may also make subtle (and sometimes not so
subtle) changes in their processing algorithms depending on whether subtle) changes in their processing algorithms depending on whether
or not the DHCP server received the message as a unicast packet from or not the DHCP server received the message as a unicast packet from
the DHCP client directly, a broadcast packet from the DHCP client on the DHCP client directly, a broadcast packet from the DHCP client on
a locally connected network, or a unicast packet from a DHCP Relay a locally connected network, or a unicast packet from a DHCP Relay
Agent which has forwarded on a packet broadcast from a DHCP client Agent, which has forwarded on a packet broadcast from a DHCP client
connected to a network local to the DHCP Relay Agent. connected to a network local to the DHCP Relay Agent.
In some situations, DHCP Clients may unicast their DHCPREQUEST/RENEW In some situations, DHCP Clients may unicast their DHCPREQUEST/RENEW
packets to the DHCP Relay Agent, which will forward the packet on to packets to the DHCP Relay Agent, which will forward the packet on to
the DHCP server. In these cases, the DHCP server cannot tell whether the DHCP server. In these cases, the DHCP server cannot tell whether
the packet was broadcast or unicast by the DHCP client, and so it may the packet was broadcast or unicast by the DHCP client, and so it may
be unable to process the DHCP client packets in the manner that it be unable to process the DHCP client packets in the manner that it
would if it knew whether the original DHCP packet was broadcast or would if it knew whether the original DHCP packet was broadcast or
unicast. For example, a server might be willing to NAK a client in unicast. For example, a server might be willing to NAK a client in
the REBINDING state based on a determination that the client's the REBINDING state based on a determination that the client's
skipping to change at page 4, line 18 skipping to change at page 3, line 18
several possible flags. The first flag defined is the unicast flag. several possible flags. The first flag defined is the unicast flag.
The format of the suboption is: The format of the suboption is:
0 1 2 0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Length | Flags | | Code | Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code The suboption code. (TBD, to be assigned by IANA). Code The suboption code (10).
Length The suboption length, 1 octet. Length The suboption length, 1 octet.
Flags The Relay Agent flags for this forwarded packet. Flags The Relay Agent flags for this forwarded packet.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|U| MBZ | |U| MBZ |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
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MBZ: MUST BE ZERO (reserved for future use) MBZ: MUST BE ZERO (reserved for future use)
4. DHCP Relay Agent Behavior 4. DHCP Relay Agent Behavior
A DHCP relay agent that claims to conform to this specification MUST A DHCP relay agent that claims to conform to this specification MUST
include this suboption in every Relay Agent Information Option include this suboption in every Relay Agent Information Option
[RFC3046] it adds to a forwarded DHCP request. In this way, the DHCP [RFC3046] it adds to a forwarded DHCP request. In this way, the DHCP
server can distinguish a request forwarded from a DHCP relay agent server can distinguish a request forwarded from a DHCP relay agent
that does not support the relay-agent-flags suboption from a request that does not support the relay-agent-flags suboption from a request
forwarded by a DHCP relay agent that supports the relay-agent-flags forwarded by a DHCP relay agent that supports the relay-agent-flags
suboption and which received the request that is being forwarded in a suboption, and which received the request that is being forwarded in
broadcast packet. a broadcast packet.
To put this another way, A DHCP relay agent which supports the relay- To put this another way, A DHCP relay agent that supports the relay-
agent-flags suboption MUST always include it in every relay-agent- agent-flags suboption MUST always include it in every relay-agent-
information-option that it inserts into packets which it forwards on information-option that it inserts into packets that it forwards on
to the DHCP server, whether the packet it is forwarding was received to the DHCP server, whether the packet it is forwarding was received
as a broadcast or as a unicast. This is because the DHCP server will as a broadcast or as a unicast. This is because the DHCP server will
be dealing with DHCP relay agents that support the relay-agent-flags be dealing with DHCP relay agents that support the relay-agent-flags
suboption as well as DHCP relay agents that do not support the relay- suboption as well as DHCP relay agents that do not support the relay-
agent-flags suboption. agent-flags suboption.
5. DHCP Server Behavior 5. DHCP Server Behavior
This option provides additional information to the DHCP server. The This option provides additional information to the DHCP server. The
DHCP server MAY use this information to make processing decisions DHCP server MAY use this information to make processing decisions
regarding the DHCP Client's packet which it is processing. For regarding the DHCP Client's packet that it is processing. For
instance, knowledge of the broadcast or unicast reception of a packet instance, knowledge of the broadcast or unicast reception of a packet
by a DHCP relay agent could be used when making the processing by a DHCP relay agent could be used when making the processing
decisions required to implement Load Balancing [RFC3074]. A load- decisions required to implement Load Balancing [RFC3074]. A load-
balancing server may be willing to respond to a REBINDING client, but balancing server may be willing to respond to a REBINDING client, but
the server cannot determine the client's state without this the server cannot determine the client's state without this
additional indication. additional indication.
The option length is one octet. If the DHCP server receives a relay- The option length is one octet. If the DHCP server receives a relay-
agent-flags suboption that is longer than one octet, it MUST evaluate agent-flags suboption that is longer than one octet, it MUST evaluate
the first octet. the first octet.
skipping to change at page 5, line 36 skipping to change at page 4, line 36
earlier implementations. If additional flags values are defined in earlier implementations. If additional flags values are defined in
the future, it will not always be possible to distinguish between the future, it will not always be possible to distinguish between
messages from relay agents who understand the new value and set its messages from relay agents who understand the new value and set its
value to 'zero', and relay agents who are simply setting a series of value to 'zero', and relay agents who are simply setting a series of
unassigned bits to 'zero'. It would be a mistake to specify unassigned bits to 'zero'. It would be a mistake to specify
significant behavior changes based on 'zero' values of flags significant behavior changes based on 'zero' values of flags
specified in the future. specified in the future.
6. Security Considerations 6. 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 [RFC3118]. band exchange of a shared secret is feasible, is defined in
Potential exposures to attack are discussed in section 7 of the DHCP [RFC3118]. Potential exposures to attack are discussed in Section 7
protocol specification in [RFC2131]. of the DHCP protocol specification in [RFC2131].
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 the DHCP relay agent and the server, as described in Section 5 of
[RFC3046]. While the introduction of fraudulent relay-agent options [RFC3046]. While the introduction of fraudulent relay-agent options
can be prevented by a perimeter defense that blocks these options can be prevented by a perimeter defense that blocks these options
unless the relay agent is trusted, a deeper defense using the unless the relay agent is trusted, a deeper defense using the
authentication option for relay agent options [RFC4030] SHOULD be authentication option for relay agent options [RFC4030] SHOULD be
deployed as well. deployed as well.
7. IANA Considerations 7. IANA Considerations
IANA is requested to assign a suboption number for the Flags IANA has assigned a suboption number (10) for the Flags Suboption
Suboption from the DHCP Relay Agent Information Option [RFC3046] from the DHCP Relay Agent Information Option [RFC3046] suboption
suboption number space. number space.
8. Acknowledgements 8. Acknowledgements
Thanks to David Hankins for realizing the problems created by the Thanks to David Hankins for realizing the problems created by the
server-id-override option draft and for helping us understand the server-id-override option document and for helping us understand the
value of finally solving this problem in a way that has general value of finally solving this problem in a way that has general
applicability. applicability.
9. References 9. References
9.1. Normative References 9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
skipping to change at page 7, line 14 skipping to change at page 6, line 14
Authors' Addresses Authors' Addresses
Kim Kinnear Kim Kinnear
Cisco Systems, Inc. Cisco Systems, Inc.
1414 Massachusetts Ave. 1414 Massachusetts Ave.
Boxborough, MA 01719 Boxborough, MA 01719
US US
Phone: +1 978 936 0000 Phone: +1 978 936 0000
Email: kkinnear@cisco.com EMail: kkinnear@cisco.com
Marie Normoyle Marie Normoyle
Cisco Systems, Inc. Cisco Systems, Inc.
1414 Massachusetts Ave. 1414 Massachusetts Ave.
Boxborough, MA 01719 Boxborough, MA 01719
US US
Phone: +1 978 936 0000 Phone: +1 978 936 0000
Email: mnormoyle@cisco.com EMail: mnormoyle@cisco.com
Mark Stapp Mark Stapp
Cisco Systems, Inc. Cisco Systems, Inc.
1414 Massachusetts Ave. 1414 Massachusetts Ave.
Boxborough, MA 01719 Boxborough, MA 01719
US US
Phone: +1 978 936 0000 Phone: +1 978 936 0000
Email: mjs@cisco.com EMail: mjs@cisco.com
Full Copyright Statement Full Copyright Statement
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
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attempt made to obtain a general license or permission for the use of attempt made to obtain a general license or permission for the use of
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.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
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