draft-ietf-dhc-relay-agent-flags-00.txt   draft-ietf-dhc-relay-agent-flags-01.txt 
DHC K. Kinnear DHC K. Kinnear
Internet-Draft M. Normoyle Internet-Draft M. Normoyle
Expires: December 10, 2006 M. Stapp Expires: December 10, 2006 M. Stapp
Cisco Systems, Inc. Cisco Systems, Inc.
June 8, 2006 June 8, 2006
DHCPv4 Relay Agent Flags Suboption DHCPv4 Relay Agent Flags Suboption
draft-ietf-dhc-relay-agent-flags-00.txt draft-ietf-dhc-relay-agent-flags-01.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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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
received the packet via a unicast or broadcast packet. This received the packet via a unicast or broadcast packet. This
information may be used by the DHCP server to better serve clients information may be used by the DHCP server to better serve clients
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 . . . . . . . . . . . . . . . . . . . . . . 3 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 . . . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
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 . . . . . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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 the DHCP server. Once the process its request and forward it on to the DHCP server. When the
lease has been granted, however, future DHCP DHCPREQUEST/RENEWAL DHCP relay performs this function, it can be configured to use the
messages are unicast directly to the DHCP Server. [RFC2131] DHCP relay agent information option to forward additional information
[RFC2132] [RFC3046] to the DHCP server, which the server may then use to alter its
processing algorithms. Once the lease has been granted, however,
future DHCP DHCPREQUEST/RENEWAL messages are unicast directly to the
DHCP Server. [RFC2131] [RFC2132] [RFC3046]
In general, DHCP servers may 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 processes 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.
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 server to know if a packet forwarded on by a DHCP Relay the DHCP relay to specify flags for the forwarded packet. These
Agent was broadcast or unicast to the DHCP Relay Agent. 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.
The DHCP server can use the information provided by the DHCP relay to
improve its processing algorithms.
One flag is defined to indicate whether the DHCP relay received the
packet via a unicast or broadcast packet. This allows the DHCP
server to know if a packet forwarded on by a DHCP Relay Agent was
broadcast or unicast to the DHCP Relay Agent.
2. Requirements Terminology 2. Requirements Terminology
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 [RFC2119]. document are to be interpreted as described in [RFC2119].
3. The Flags Suboption 3. The Flags Suboption
The Flags suboption provides an extensible suboption definition for The Flags suboption provides an extensible suboption definition for
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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. (TBD, to be assigned by IANA).
Length The suboption length, 1 byte. 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 |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
U: UNICAST flag U: UNICAST flag
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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 is important when making the processing
decisions required to implement Load Balancing [RFC3074]. decisions required to implement Load Balancing [RFC3074].
The option length is one byte. 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 byte, it MUST evaluate agent-flags suboption that is longer than one octet, it MUST evaluate
the first octet. the first octet.
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
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