DHC Lu Huang
Internet Draft Hui Deng
Intended status: Informational China Mobile
Expires: April 18, 2010 October 19, 2009
DHCP option including Multiple Relay Agents' Information
draft-huang-dhc-multiple-relay-agents-option-00.txt
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Abstract
RFC 3046 allows only the first Relay Agent to append Relay Agent
Information option. In some networks, both Layer 2 Relay Agents and
Layer 3 Relay Agents are deployed and their information is necessary
for DHCP packets forwarding and DHCP server's policy designing
described as [4]. This document defines a DHCP option which can
contain multiple relay agents' information and describes how it works.
Table of Contents
1. Introduction......................................... 2
2. DHCP option including Multiple Relay Agents' Information .... 3
2.1. Mechanism....................................... 3
2.2. Format ......................................... 4
3. Security Considerations................................ 5
4. IANA Considerations................................... 5
5. References.......................................... 5
5.1. Normative References.............................. 5
5.2. Informative References............................ 5
Author's Addresses...................................... 6
1. Introduction
As defined in RFC 3046, Relay Agent Information option is inserted by
the DHCP relay agent (or downstream network element) when forwarding
client-originated DHCP packets to a DHCP server. Servers recognizing
the Relay Agent Information option may use the information to
implement IP address or other parameter assignment policies. The DHCP
Server echoes the option back verbatim to the relay agent in server-
to-client replies, and the relay agent strips the option before
forwarding the reply to the client.
RFC 3046 allows only one agent add its information with option 82.
But in some scenarios as [4], multiply relay agents need to insert
more information into the same DHCP message. This document defines a
DHCP option which can contain multiple relay agents' information and
describes how it works.
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2. DHCP option including Multiple Relay Agents' Information
2.1. Mechanism
This option is organized as a single DHCP option that contains one or
more sub-options. Each relay agent can insert a set of sub-options to
convey its Information.
-------
+-----------+ +-----------+ /// \\\ +------+
+------+ |Layer 2 | |Layer 3 | | | |DHCP |
|Client+--+Relay Agent+--+Relay Agent+--+ Network +--+Server|
+------+ +-----------+ +-----------+ | | +------+
\\\ ///
-------
Figure 1 Network Scenario
As shown in figure 1, it's a most popular network scenario where
option including Multiple Relay Agents' Information is necessary.
Based on the demand of the new Relay Agent Information option as [4],
this option works as following:
1. An initiating client sends a DHCP discovery packet.
2. Layer 2 relay agent receives the discovery packet without any
options defined in this document. So it inserts a new option in
which a set of sub-options convey the layer 2 relay agent's
necessary information. After that, the discovery packet is
forwarded to the appropriate port.
3. Layer 3 relay agent receives the discovery packet and check out
that it already contains a relay agent information option defined
in this document. So it just insert a set of sub-options into the
existing option to convey its own necessary information. After
that, the discovery packet is forwarded and reaches DHCP server
directly or through a network.
4. DHCP server handles the discovery packet as normal and could carry
out flexible IP assigning or other policies based on the
information of option defined in this document. After that DHCP
server reply a DHCP response packet containing the original option
carried in the corresponding discovery packet.
5. Layer 3 relay agents quickly get the right outgoing interface
based on the information in the option and forward the response
packet after deleting its set of sub-options.
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6. Layer 2 relay agents quickly get the right outgoing interface
based on the information in the option and forward the response
packet. Because there is no other agent's information left in the
option, so in this case layer 2 relay agent delete the whole
option before forwarding the packet.
2.2. Format
Option format:
+-------+-----+-----+
|Code(x)| Len |Value|
+-------+-----+-----+
This option use a new DHCP option code "x".
Value:
+-----------+-----------+-----------+-----------+
|sub-option1|sub-option2|sub-option3|sub-option4|
+-+--+------+-+--+------+-+--+------+-+--+------+
|1|N1|value1|2|N2|value2|3|N3|value3|4|N4|value4|->a Set of sub-options
+-+--+------+-+--+------+-+--+------+-+--+------+
/ ... \
| Multiple sets of sub-options |
\ ... /
+-+--+------+-+--+------+-+--+------+-+--+------+
|1|N1|value1|2|N2|value2|3|N3|value3|4|N4|value4|
+-+--+------+-+--+------+-+--+------+-+--+------+
Sub-option1
Agent level. Describe the order of agent who insert this set of
sub-options. For example, in the case of figure 1, layer 2 relay
agent's level is 1 because it is the closest agent to the client
and it will be the first agent who insert relay agent information.
Sub-option2
Agent ID. Describe a unique identifier for the agent who insert
this set of sub-options.
Sub-option3
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IP address. Describe IP address of the agent who insert this set
of sub-options. For a pure layer 2 agent, this field could be
0.0.0.0.
Sub-option4
Downstream interface. Describe the receiving interface of the
DHCP packet of the agent who insert this set of sub-options.
3. Security Considerations
This document doesn't propose any new protocol.
4. IANA Considerations
This document requires a new number for DHCP option code x described
in section 2.2.
5. References
5.1. Normative References
[1] R. Droms, Bucknell University, "Dynamic Host Configuration
Protocol", RFC 2131, March 1997.
[2] S. Alexander, Silicon Graphics, Inc., and R. Droms, "DHCP Options
and BOOTP Vendor Extensions", RFC 2132, March 1997.
[3] M. Patrick, Motorola BCS, "DHCP Relay Agent Information Option",
RFC 3046, January 2001.
5.2. Informative References
[4] L. Huang, H. Deng, China Mobile, "Problem Statement for DHCP Relay
Agent", draft-huang-dhc-relay-ps-00, July 2009.
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Author's Addresses
Lu Huang
China Mobile
53A,Xibianmennei Ave.,
Xuanwu District,
Beijing 100053
China
Email: huanglu@chinamobile.com
Hui Deng
China Mobile
53A,Xibianmennei Ave.,
Xuanwu District,
Beijing 100053
China
Email: denghui02@gmail.com
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