One document matched: draft-huang-dhc-relay-ps-00.txt
DHC L. Huang, Ed.
Internet-Draft H. Deng
Intended status: Informational China Mobile
Expires: January 6, 2010 P. Kurapati
B. Joshi
Infosys Technologies
July 5, 2009
Problem Statement for DHCP Relay Agent
draft-huang-dhc-relay-ps-00
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Internet-Draft DHCP Relay PS July 2009
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Abstract
RFC 3046 allows only the first Relay Agent to append Relay Agent
Information option. In some networks, Layer 2 Relay Agents and Layer
3 Relay Agents are deployed but only Layer 2 Relay Agent appends the
Relay Agent Information option. This document describes two pretty
common network scenarios that uses Layer 2 and Layer 3 Relay Agents
and their unique requirements where either DHCP server or Relay Agent
need more information to handle DHCP messages.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Identifying the downstream subscriber's interface . . . . . . . 4
3. location based authentication . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
5. IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Introduction
DHCP Relay Agents eliminate the necessity of having a DHCP server on
each physical network. RFC 3046 introduces Relay Agent Information
option which is inserted by DHCP relay agent when forwarding client-
originated DHCP packets to a DHCP server. DHCP server may use the
information available in this option to implement IP address or other
parameter assignment policies. DHCP server echo back the Relay Agent
Information option in the reply messages and Relay Agent strips this
option before forwarding the reply to the client.
In some network configurations, DHCP server and clients are separated
by multiple Relay Agents. This document describes two such network
scenarios and their unique requirements in details. This document is
intended to be a problem statement document and document the problems
and thier requirements. This document does not suggest any specific
ways to solve these problems.
2. Identifying the downstream subscriber's interface
-------
+-----------+ +-----------+ /// \\\ +------+
+------+ |Layer 2 | |Layer 3 | | | |DHCP |
|Client+--+Relay Agent+--+Relay Agent+--+ Network +--+Server|
+------+ +-----------+ +-----------+ | | +------+
\\\ ///
-------
Figure 1: Network Scenario
Under current mechanism defined in RFC3046, only downstream relay
agent can insert relay agent information. In some deployments, Layer
3 Relay Agent uses unnumbered interfaces. When these Layer 3 Relay
Agents are used along with Layer 2 Relay agents, they need to
maintain internal states to identify the outgoing interface.
Maintaining state information for each packet will not scale as
number of DHCP clients increases.
3. location based authentication
When IPoE is used as access authentication mechanism, clients'
location is recognized through DHCP relay agent information.
Sometime, operator may limit the ability of access of subscriber
within the pre-arranged area, such as a certain building. But in the
current deployment, relay agent information can be inserted either by
the floor switches or the building switches, which means that the
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subscriber!_s location is either too specific or too ambiguous. It
will need much more policies for the operator to configure the
subscriber's right to access from various kind of location scenario.
For example, a layer 3 switch is installed for a 20 floor building
and a layer 2 switch is installed at each floor inside this building.
+-------+
Layer 3 |Layer 3|
Relay Agent |Switch |
-+---/---+---
--- / ----
-- / ----
--- / -----
+-------+ | +---/---+ | | +-------+
Layer 2 |Layer 2| | |Layer 2| | ....... | |Layer 2|
Relay Agent |Switch | | |Switch | | | |Switch |
+-------+ | +-------+ | | +-------+
| | |
floor 1 | floor 2 | | floor 20
Figure 2: Network Scenario
If the administrator plan to allow client A to access only from the
first floor of this building and allow client B to access from every
each floor. Based on the current mechanism, relay agent option
information can only be inserted by layer 2 switch and the
administrator should make 21 policies, one for client A and twenty
for client B in this scenario. If Layer 3 switch can also insert
some relay agent information even if layer 2 switch has inserted one,
the administrator only need to make 2 policies, one for client A and
the other for client B.
4. Security Considerations
This is a problem statement document and does not suggest any
protocol functionality.
5. IANA Consideration
This document makes no requests to IANA.
6. References
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6.1. Normative References
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
[RFC3046] Patrick, M., "DHCP Relay Agent Information Option",
RFC 3046, January 2001.
6.2. Informative References
[Relay Chaining]
Joshi, B., "Relay Chaining in DHCPv4",
draft-kurapati-dhc-relay-chaining-dhcpv4-01.txt (work in
progress), June 2007.
Authors' Addresses
Lu Huang (editor)
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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Pavan Kurapati
Infosys Technologies
44 Electronics City, Hosur Road
Bangalore 560100
India
Email: pavan_kurapati@infosys.com
Bharat Joshi
Infosys Technologies
44 Electronics City, Hosur Road
Bangalore 560100
India
Email: bharat_joshi@infosys.com
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