draft-ietf-dhc-l2ra-05.txt   draft-ietf-dhc-l2ra-06.txt 
DHC Working Group B. Joshi DHC B. Joshi
Internet-Draft Infosys Technologies Ltd. Internet-Draft Infosys Ltd.
Intended status: Informational P. Kurapati Intended status: Informational P. Kurapati
Expires: October 9, 2011 Juniper Networks Expires: July 28, 2012 Juniper Networks
April 7, 2011 January 25, 2012
Layer 2 Relay Agent Information Layer 2 Relay Agent Information
draft-ietf-dhc-l2ra-05.txt draft-ietf-dhc-l2ra-06.txt
Abstract Abstract
In some networks, DHCP servers rely on Relay Agent Information option In some networks, DHCP servers rely on Relay Agent Information option
appended by Relay Agents for IP address and other parameter appended by Relay Agents for IP address and other parameter
assignment policies. This works fine when end hosts are directly assignment policies. This works fine when end hosts are directly
connected to Relay Agents. In some network configurations, one or connected to Relay Agents. In some network configurations, one or
more Layer 2 devices may reside between DHCP clients and Relay agent. more Layer 2 devices may reside between DHCP clients and Relay agent.
In these network scenarios, it is difficult to use the Relay Agent In these network scenarios, it is difficult to use the Relay Agent
Information option for IP address and other parameter assignment Information option for IP address and other parameter assignment
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Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Need of Layer 2 Relay Agent . . . . . . . . . . . . . . . . . 5 3. Need of Layer 2 Relay Agent . . . . . . . . . . . . . . . . . 4
4. Layer 2 Relay Agent in various network scenarios . . . . . . . 6 4. Layer 2 Relay Agent in various network scenarios . . . . . . . 5
4.1. DHCP server and client on same subnet . . . . . . . . . . 6 4.1. DHCP server and client on same subnet . . . . . . . . . . 5
4.1.1. Client-server interaction . . . . . . . . . . . . . . 6 4.1.1. Client-server interaction . . . . . . . . . . . . . . 5
4.1.2. Issues due to introduction of Layer 2 Relay Agent . . 8 4.1.2. Issues due to introduction of Layer 2 Relay Agent . . 7
4.2. Multiple DHCP server and Client on same subnet . . . . . . 8 4.2. Multiple DHCP server and Client on same subnet . . . . . . 7
4.2.1. Client-server interaction . . . . . . . . . . . . . . 9 4.2.1. Client-server interaction . . . . . . . . . . . . . . 8
4.2.2. Issues due to introduction of Layer 2 Relay Agent . . 9 4.2.2. Issues due to introduction of Layer 2 Relay Agent . . 8
4.3. DHCP server on another subnet with one Layer 3 Relay 4.3. DHCP server on another subnet with one Layer 3 Relay
Agent . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Agent . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.3.1. Client-server interaction . . . . . . . . . . . . . . 10 4.3.1. Client-server interaction . . . . . . . . . . . . . . 9
4.3.2. Issues due to introduction of Layer 2 Relay Agent . . 12 4.3.2. Issues due to introduction of Layer 2 Relay Agent . . 11
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14 6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative Reference . . . . . . . . . . . . . . . . . . . 16 8.1. Normative References . . . . . . . . . . . . . . . . . . . 12
8.2. Informative Reference . . . . . . . . . . . . . . . . . . 16 8.2. Informative Reference . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction 1. Introduction
DHCP Relay Agents eliminate the necessity of having a DHCP server on DHCP Relay Agents eliminate the necessity of having a DHCP server on
each physical network. Relay Agents populate the 'giaddr' field and each physical network. Relay Agents populate the 'giaddr' field and
also append the 'Relay Agent Information' option to the DHCP also append the 'Relay Agent Information' option to the DHCP
messages. DHCP servers use this option for IP address and other messages. DHCP servers use this option for IP address and other
parameter assignment policies. These DHCP Relay Agents are typically parameter assignment policies. These DHCP Relay Agents are typically
an IP routing aware device and are referred as Layer 3 Relay Agents. an IP routing aware device and are referred as Layer 3 Relay Agents.
skipping to change at page 4, line 22 skipping to change at page 3, line 46
o "DHCP client" o "DHCP client"
A DHCP client is an Internet host using DHCP to obtain configuration A DHCP client is an Internet host using DHCP to obtain configuration
parameters such as a network address. parameters such as a network address.
o "Layer 3 Relay Agent" o "Layer 3 Relay Agent"
A Layer 3 Relay Agent is a third-party agent that transfers Bootstrap A Layer 3 Relay Agent is a third-party agent that transfers Bootstrap
Protocol (BOOTP) and DHCP messages between clients and servers Protocol (BOOTP) and DHCP messages between clients and servers
residing on different subnets, per [RFC951] and [RFC1542]. residing on different subnets, per [RFC0951] and [RFC1542].
o "BRAS" o "BRAS"
BRAS or Broadband Remote Access Server is a network element which BRAS or Broadband Remote Access Server is a network element which
acts as an aggregation device terminating end user sessions. BRAS is acts as an aggregation device terminating end user sessions. BRAS is
usually the first IP edge device in a Layer 2 Access Network usually the first IP edge device in a Layer 2 Access Network
architecture. architecture.
o "DHCP server" o "DHCP server"
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4.1. DHCP server and client on same subnet 4.1. DHCP server and client on same subnet
In certain network configurations, a DHCP server may reside on the In certain network configurations, a DHCP server may reside on the
same subnet as the DHCP clients. A Layer 2 aggregation device same subnet as the DHCP clients. A Layer 2 aggregation device
resides between the DHCP clients and DHCP server. The following resides between the DHCP clients and DHCP server. The following
points describe how this Layer 2 device handles various DHCP messages points describe how this Layer 2 device handles various DHCP messages
if it acts as a Layer 2 Relay Agent. Figure 1 shows a typical if it acts as a Layer 2 Relay Agent. Figure 1 shows a typical
network setup. network setup.
+--------+ +--------+
| End | +--------+ | | End | +--------+ |
| Host#1 +-----------| | | +-----------+ | Host#1 +-----------| | | +-----------+
+--------+ | Layer +-----| | | +--------+ | Layer +-----| | |
| 2 | +-----| DHCP | | 2 | +-----| DHCP |
+--------+ | device | | | Server#1 | +--------+ | device | | | Server#1 |
| End +-----------| #1 | | +-----------+ | End +-----------| #1 | | +-----------+
| Host#2 | +--------+ | | Host#2 | +--------+ |
+--------+ | +--------+ |
| |
+--------+ | +--------+ |
| End | +--------+ | | End | +--------+ |
| Host#3 +-----------| | | | Host#3 +-----------| | |
+--------+ | Layer +-----| +--------+ | Layer +-----|
| 2 | | | 2 | |
+--------+ | device | | +--------+ | device | |
| End +-----------| #2 | | End +-----------| #2 |
| Host#n | +--------+ | Host#n | +--------+
+--------+ +--------+
Figure 1 Figure 1
4.1.1. Client-server interaction 4.1.1. Client-server interaction
The following summary of protocol message exchanges between clients The following summary of protocol message exchanges between clients
and DHCP servers describes how they are handled in a Layer 2 Relay and DHCP servers describes how they are handled in a Layer 2 Relay
Agent. Agent.
1. The client (End Host #1) broadcasts a DHCPDISCOVER message on its 1. The client (End Host #1) broadcasts a DHCPDISCOVER message on its
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3. A DHCP server should be able to handle a unicast DHCP message 3. A DHCP server should be able to handle a unicast DHCP message
containing a Relay Agent Information option. Some existing DHCP containing a Relay Agent Information option. Some existing DHCP
server implementations do not echo back the Relay Agent server implementations do not echo back the Relay Agent
Information option in responses to unicast messages. Information option in responses to unicast messages.
4.2. Multiple DHCP server and Client on same subnet 4.2. Multiple DHCP server and Client on same subnet
In certain network scenarios, there could be multiple DHCP servers on In certain network scenarios, there could be multiple DHCP servers on
the same subnet. Figure 2 shows a typical network setup. the same subnet. Figure 2 shows a typical network setup.
+--------+ +--------+
| End | +--------+ | | End | +--------+ |
| Host#1 +-----------| | | +-----------+ | Host#1 +-----------| | | +-----------+
+--------+ | Layer +-----| | | +--------+ | Layer +-----| | |
| 2 | +-----| DHCP | | 2 | +-----| DHCP |
+--------+ | device | | | Server#1 | +--------+ | device | | | Server#1 |
| End +-----------| #1 | | +-----------+ | End +-----------| #1 | | +-----------+
| Host#2 | +--------+ | | Host#2 | +--------+ |
+--------+ | +--------+ |
| +-----------+ | +-----------+
+--------+ | | DHCP | +--------+ | | DHCP |
| End | +--------+ |-----| Server #2 | | End | +--------+ |-----| Server #2 |
| Host#3 +-----------| | | | | | Host#3 +-----------| | | | |
+--------+ | Layer +-----| +-----------+ +--------+ | Layer +-----| +-----------+
| 2 | | | 2 | |
+--------+ | device | +--------+ | device |
| End +-----------| #2 | | End +-----------| #2 |
| Host#n | +--------+ | Host#n | +--------+
+--------+ +--------+
Figure 2 Figure 2
4.2.1. Client-server interaction 4.2.1. Client-server interaction
The message exchanges are the same as explained in 4.1.1. However, The message exchanges are the same as explained in 4.1.1. However,
due to the introduction of multiple DHCP servers the below additional due to the introduction of multiple DHCP servers the below additional
message exchange may happen. message exchange may happen.
1. When Host #1 sends DHCPDISCOVER, it will be received by both DHCP 1. When Host #1 sends DHCPDISCOVER, it will be received by both DHCP
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2. Other issues are the same as described in section 4.1.2. 2. Other issues are the same as described in section 4.1.2.
4.3. DHCP server on another subnet with one Layer 3 Relay Agent 4.3. DHCP server on another subnet with one Layer 3 Relay Agent
In certain network scenarios, there could be a Layer 3 Relay Agent In certain network scenarios, there could be a Layer 3 Relay Agent
which relays the DHCP messages from one subnet to a DHCP server on which relays the DHCP messages from one subnet to a DHCP server on
another subnet and vice versa. In typical deployments, the Access another subnet and vice versa. In typical deployments, the Access
Concentrator acts as Layer 2 Relay Agent and the IP edge device (BRAS Concentrator acts as Layer 2 Relay Agent and the IP edge device (BRAS
or IP Services Switch) acts as Layer 3 Relay Agent. or IP Services Switch) acts as Layer 3 Relay Agent.
+--------+ +--------+
| End | +--------+ | | | End | +--------+ | |
| Host#1 +--------| | | +-----------+ | | Host#1 +--------| | | +-----------+ |
+--------+ | Layer +-----| | | | +--------+ | Layer +-----| | | |
| 2 | +--| Layer 3 |----| | 2 | +--| Layer 3 |----|
+--------+ | device | | | Relay | | +--------+ | device | | | Relay | |
| End +--------| #1 | | | Agent #1 | | | End +--------| #1 | | | Agent #1 | |
| Host#2 | +--------+ | +-----------+ | +---------+ | Host#2 | +--------+ | +-----------+ | +---------+
+--------+ | | | | +--------+ | | | |
| +--| DHCP | | +--| DHCP |
+--------+ | | | Server | +--------+ | | | Server |
| End | +--------+ | | | #1 | | End | +--------+ | | | #1 |
| Host#3 +--------| | | +---------+ | Host#3 +--------| | | +---------+
+--------+ | Layer +-----| +--------+ | Layer +-----|
| 2 | | | 2 | |
+--------+ | device | | +--------+ | device | |
| End +--------| #2 + | End +--------| #2 +
| Host#n | +--------+ | Host#n | +--------+
+--------+ +--------+
Figure 3 Figure 3
4.3.1. Client-server interaction 4.3.1. Client-server interaction
As far as DHCP message processing is concerned, the presence of Layer As far as DHCP message processing is concerned, the presence of Layer
3 Relay Agents is transparent to Layer 2 Relay Agents. So all the 3 Relay Agents is transparent to Layer 2 Relay Agents. So all the
messages are handled in the same way as defined in section 4.1.1 for messages are handled in the same way as defined in section 4.1.1 for
the Layer 2 Relay Agent. the Layer 2 Relay Agent.
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new security issues. Security issues pertaining to Relay Agents new security issues. Security issues pertaining to Relay Agents
in general apply to Layer 2 Relay Agents as well. in general apply to Layer 2 Relay Agents as well.
7. IANA Considerations 7. IANA Considerations
This document does not introduce any new namespaces for the IANA to This document does not introduce any new namespaces for the IANA to
manage and does not request any new code point assignments. manage and does not request any new code point assignments.
8. References 8. References
8.1. Normative Reference 8.1. 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.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", [RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997. RFC 2131, March 1997.
[RFC3046] Patrick, M., "DHCP Relay Agent Information Option", [RFC3046] Patrick, M., "DHCP Relay Agent Information Option",
RFC 3046, January 2001. RFC 3046, January 2001.
[RFC3118] Droms, R. and B. Arbaugh, "Authentication for DHCP
Messages", RFC 3118, June 2001.
[RFC3232] Reynolds, J., "Assigned Numbers", RFC 3232, January 2002.
8.2. Informative Reference 8.2. Informative Reference
[RFC951] Croft, B. and J. Gilmore, "Bootstrap Protocol (BOOTP)", [RFC0951] Croft, B. and J. Gilmore, "Bootstrap Protocol", RFC 951,
RFC 951, September 1985. September 1985.
[RFC1542] Wimer, W., "Clarifications and Extensions for the [RFC1542] Wimer, W., "Clarifications and Extensions for the
Bootstrap Protocol", RFC 1542, October 1993. Bootstrap Protocol", RFC 1542, October 1993.
[RFC2132] Droms, R. and S. Alexander, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
Authors' Addresses Authors' Addresses
Bharat Joshi Bharat Joshi
Infosys Technologies Ltd. Infosys Ltd.
44 Electronics City, Hosur Road 44 Electronics City, Hosur Road
Bangalore 560 100 Bangalore 560 100
India India
Email: bharat_joshi@infosys.com Email: bharat_joshi@infosys.com
URI: http://www.infosys.com/ URI: http://www.infosys.com/
Pavan Kurapati Pavan Kurapati
Juniper Networks Juniper Networks
Embassy Prime Buildings, C.V. Raman Nagar Embassy Prime Buildings, C.V. Raman Nagar
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