draft-ietf-dhc-relay-agent-flags-02.txt   draft-ietf-dhc-relay-agent-flags-03.txt 
DHC K. Kinnear DHC K. Kinnear
Internet-Draft M. Normoyle Internet-Draft M. Normoyle
Intended status: Standards Track M. Stapp Intended status: Standards Track M. Stapp
Expires: August 2, 2007 Cisco Systems, Inc. Expires: October 25, 2007 Cisco Systems, Inc.
January 29, 2007 April 23, 2007
DHCPv4 Relay Agent Flags Suboption DHCPv4 Relay Agent Flags Suboption
draft-ietf-dhc-relay-agent-flags-02.txt draft-ietf-dhc-relay-agent-flags-03.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
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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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
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 2, 2007. This Internet-Draft will expire on October 25, 2007.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
Abstract Abstract
This memo defines a new suboption of the DHCP relay agent information This memo defines a new suboption of the DHCP relay agent information
option that allows the DHCP relay to specify flags for the forwarded option that allows the DHCP relay to specify flags for the forwarded
packet. One flag is defined to indicate whether the DHCP relay packet. One flag is defined to indicate whether the DHCP relay
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based on whether their request was originally broadcast or unicast. based on whether their request was originally broadcast or unicast.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Terminology . . . . . . . . . . . . . . . . . . . 3 2. Requirements Terminology . . . . . . . . . . . . . . . . . . . 3
3. The Flags Suboption . . . . . . . . . . . . . . . . . . . . . . 4 3. The Flags Suboption . . . . . . . . . . . . . . . . . . . . . . 4
4. DHCP Relay Agent Behavior . . . . . . . . . . . . . . . . . . . 4 4. DHCP Relay Agent Behavior . . . . . . . . . . . . . . . . . . . 4
5. DHCP Server Behavior . . . . . . . . . . . . . . . . . . . . . 5 5. DHCP Server Behavior . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . . 6 9.1. Normative References . . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . . 6 9.2. Informative References . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 8 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
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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. unicast. For example, a server might be willing to NAK a client in
the REBINDING state based on a determination that the client's
address does not match its location in the network, but might not be
willing to do so if the client is in the RENEWING state.
The purpose of the suboption described in this document is to allow The purpose of the suboption described in this document is to allow
the DHCP relay to specify flags for the forwarded packet. These the DHCP relay to specify flags for the forwarded packet. These
flags can be used to describe DHCP client attributes that are useful flags can be used to describe DHCP client attributes that are useful
to the DHCP server, but can only be detected by the local DHCP relay. to the DHCP server, but can only be detected by the local DHCP relay.
The DHCP server can use the information provided by the DHCP relay to The DHCP server can use the information provided by the DHCP relay to
improve its processing algorithms. improve its processing algorithms.
One flag is defined to indicate whether the DHCP relay received the One flag is defined to indicate whether the DHCP relay received the
packet via a unicast or broadcast packet. This allows the DHCP packet via a unicast or broadcast packet. This allows the DHCP
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U: UNICAST flag U: UNICAST flag
unicast = 1 unicast = 1
broadcast = 0 broadcast = 0
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 MUST include this suboption in every Relay Agent A DHCP relay agent that claims to conform to this specification MUST
Information Option [RFC3046] it adds to a forwarded DHCP request. In include this suboption in every Relay Agent Information Option
this way, the DHCP server can distinguish a request forwarded from a [RFC3046] it adds to a forwarded DHCP request. In this way, the DHCP
DHCP relay agent which does not support the relay-agent-flags server can distinguish a request forwarded from a DHCP relay agent
suboption from a request forwarded by a DHCP relay agent which that does not support the relay-agent-flags suboption from a request
supports the relay-agent-flags suboption and which received the forwarded by a DHCP relay agent that supports the relay-agent-flags
request that is being forwarded in a broadcast packet. suboption and which received the request that is being forwarded in 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 which 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 which 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 which 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 is important when making the processing by a DHCP relay agent could be used when making the processing
decisions required to implement Load Balancing [RFC3074]. decisions required to implement Load Balancing [RFC3074]. A load-
balancing server may be willing to respond to a REBINDING client, but
the server cannot determine the client's state without this
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.
Note to implementors: In specifying the behavior of new flags bits in
the future, careful attention must be paid to compatibility with
earlier implementations. If additional flags values are defined in
the future, it will not always be possible to distinguish between
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
unassigned bits to 'zero'. It would be a mistake to specify
significant behavior changes based on 'zero' values of flags
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 [RFC3118].
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 [RFC2131]. 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
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