draft-ietf-dhc-leasequery-by-remote-id-03.txt   draft-ietf-dhc-leasequery-by-remote-id-04.txt 
DHC Working Group P. Kurapati DHC Working Group P. Kurapati
Internet-Draft R. Desetti Internet-Draft
Expires: April 29, 2010 B. Joshi Expires: May 27, 2010 R. Desetti
B. Joshi
Infosys Technologies Ltd. Infosys Technologies Ltd.
October 26, 2009 November 23, 2009
DHCPv4 Leasequery by relay agent remote ID DHCPv4 Leasequery by relay agent remote ID
draft-ietf-dhc-leasequery-by-remote-id-03.txt draft-ietf-dhc-leasequery-by-remote-id-04.txt
Abstract
Some Relay Agents extract lease information from the DHCP message
exchanged between the client and DHCP server. This lease information
is used by relay agents for various purposes like antispoofing and
prevention of flooding. RFC 4388 defines a mechanism for relay
agents to retrieve the lease information from the DHCP server as and
when this information is lost. The existing leasequery mechanism is
data driven, which means that a relay agent can initiate the
leasequery only when it starts receiving data from/to the clients.
In certain scenarios, this model is not scalable. This document
first looks at issues in existing mechanism and then proposes a new
query type, query by remote ID, to address these issues.
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and 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
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
skipping to change at page 1, line 33 skipping to change at page 1, line 48
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 April 29, 2010. This Internet-Draft will expire on May 27, 2010.
Copyright Notice Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of Provisions Relating to IETF Documents
publication of this document (http://trustee.ietf.org/license-info). (http://trustee.ietf.org/license-info) in effect on the date of
Please review these documents carefully, as they describe your rights publication of this document. Please review these documents
and restrictions with respect to this document. carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
Abstract include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
Some Relay Agents extract lease information from the DHCP message described in the BSD License.
exchanged between the client and DHCP server. This lease information
is used by relay agents for various purposes like antispoofing,
prevention of flooding. RFC 4388 defines a mechanism for relay
agents to retrieve the lease information from the DHCP server as and
when this information is lost. Existing leasequery mechanism is data
driven which means that a relay agent can initiate the leasequery
only when it starts receiving data from/to the clients. In certain
scenarios, this model is not scalable. This document first looks at
issues in existing mechanism and then proposes a new query type,
query by remote ID, to address these issues.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Design Goals . . . . . . . . . . . . . . . . . . . . . . . . . 9 4. Design Goals . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. Information Acquisition before Data Starts . . . . . . . . 9 4.1. Information Acquisition before Data Starts . . . . . . . . 9
4.2. Lessen Negative Caching . . . . . . . . . . . . . . . . . 9 4.2. Reduce Negative Caching . . . . . . . . . . . . . . . . . 9
4.3. Antispoofing in 'Fast Path' . . . . . . . . . . . . . . . 9 4.3. Antispoofing in 'Fast Path' . . . . . . . . . . . . . . . 9
5. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 10 5. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 10
6. Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 11 6. Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. Sending the DHCPLEASEQUERY Message . . . . . . . . . . . . 11 6.1. Sending the DHCPLEASEQUERY Message . . . . . . . . . . . . 11
6.2. Receiving the DHCPLEASEQUERY Message . . . . . . . . . . . 12 6.2. Receiving the DHCPLEASEQUERY Message . . . . . . . . . . . 12
6.3. Responding to the DHCPLEASEQUERY Message . . . . . . . . . 12 6.3. Responding to the DHCPLEASEQUERY Message . . . . . . . . . 12
6.4. Determining the IP address to be used in response . . . . 12 6.4. Determining the IP address to be used in the response . . 12
6.5. Building a DHCPLEASEUNKNOWN or DHCPLEASEACTIVE Messages . 13 6.5. Building a DHCPLEASEUNKNOWN or DHCPLEASEACTIVE Message . . 13
6.6. Sending a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message . . 15 6.6. Sending a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message . . 14
6.7. Receiving a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message . 15 6.7. Receiving a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message . 15
6.8. Receiving No Response to the DHCPLEASEQUERY Message . . . 15 6.8. Receiving No Response to the DHCPLEASEQUERY Message . . . 15
6.9. Lease Binding Data Storage Requirements . . . . . . . . . 15 6.9. Lease Binding Data Storage Requirements . . . . . . . . . 15
6.10. Using the DHCPLEASEQUERY Message with Multiple DHCP 6.10. Using the DHCPLEASEQUERY Message with Multiple DHCP
Servers . . . . . . . . . . . . . . . . . . . . . . . . . 16 Servers . . . . . . . . . . . . . . . . . . . . . . . . . 16
7. RFC 4388 Considerations . . . . . . . . . . . . . . . . . . . 17 7. RFC 4388 Considerations . . . . . . . . . . . . . . . . . . . 17
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18 8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
11.1. Normative Reference . . . . . . . . . . . . . . . . . . . 21 11.1. Normative Reference . . . . . . . . . . . . . . . . . . . 21
11.2. Informative Reference . . . . . . . . . . . . . . . . . . 21 11.2. Informative Reference . . . . . . . . . . . . . . . . . . 21
Appendix A. Why a New Leasequery is Required? . . . . . . . . . . 22 Appendix A. Why a New Leasequery is Required? . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction 1. Introduction
DHCP relay agents snoop DHCP messages and append relay agent DHCP relay agents snoop DHCP messages and append a relay agent
information option before relaying it to the configured DHCP Servers. information option before relaying them to the configured DHCP
In this process, some relay agents also glean the lease information Server. In this process, some relay agents also glean the lease
sent by the server and maintain this locally. This information is information sent by the server and maintain this locally. This
used for prevention of spoofing attempts from the clients and also information is used to prevent spoofing attempts from clients and
sometimes used to install routing information. When relay agent also sometimes to install routing information. When a relay agent
reboots, this information is lost. RFC 4388 [RFC4388] has defined a reboots, this information is lost. RFC 4388 [RFC4388] has defined a
mechanism to retrieve this lease information from the DHCP server. mechanism to retrieve this lease information from the DHCP server.
The existing query types defined by RFC 4388 [RFC4388] are data The existing query types defined by RFC 4388 [RFC4388] are data-
driven. When client initiates data, based on the source MAC/IP driven. When a client sends data upstream, the relay agent can query
address, relay agent can query the server about the lease the server about the related lease information, based on the source
information. These mechanisms do not scale well when there are MAC/IP address. These mechanisms do not scale well when there are
thousands of clients connected to the relay agent. In data driven thousands of clients connected to the relay agent. In the data-
model, DHCP Leasequery does not provide all the active Lease driven model, DHCP Leasequery does not provide the full, consolidated
informations associated with a given connection/circuit [consolidated active Lease informations associated with a given connection/circuit
information] which will result into an inefficient anti-spoofing. It which will result in inefficient anti-spoofing. The relay agent also
also has to contend with considerable resources for negative caching has to contend with considerable resources for negative caching
specially under spoof attacks. specially under spoofing attacks.
We need a mechanism for relay agent to retrieve the consolidated We need a mechanism for a relay agent to retrieve the consolidated
lease information for a given connection/circuit before traffic is lease information for a given connection/circuit before upstream
initiated by the clients. traffic is sent by the clients.
+--------+ +--------+
| DHCP | +--------------+ | DHCP | +--------------+
| Server |-...-| DSLAM | | Server |-...-| DSLAM |
| | | Relay Agent | | | | Relay Agent |
+--------+ +--------------+ +--------+ +--------------+
| | | |
+------+ +------+ +------+ +------+
|Modem1| |Modem2| |Modem1| |Modem2|
+------+ +------+ +------+ +------+
| | | | | |
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
|Host1| |Host2| |Host3| |Host1| |Host2| |Host3|
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
Figure 1 Figure 1
For example, when a DSLAM acting as a Relay Agent is rebooted, it For example, when a DSLAM acting as a Relay Agent is rebooted, it
should query the server for the lease information for all the should query the server for the lease information for all the
connections/circuits. Also, as shown in the above figure, there connections/circuits. Also, as shown in the above figure, there
could be multiple clients on one DSL circuit. Relay agent should get could be multiple clients on one DSL circuit. The relay agent should
the lease information of all the clients connected to a DSL circuit. get the lease information of all the clients connected to a DSL
This is possible by introducing a new query type based on the Remote circuit. This is possible by introducing a new query type based on
Id sub-option of Relay Agent Information option. This document talks the Remote Id sub-option of the Relay Agent Information option. This
about the motivation for the new query type and the method to do the document talks about the motivation for the new query type and the
same. method to perform it.
2. Terminology 2. 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 RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
This document uses the following terms: This document uses the following terms:
o "access concentrator" o "access concentrator"
skipping to change at page 5, line 29 skipping to change at page 5, line 29
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 "DHCP relay agent" o "DHCP relay agent"
A DHCP relay agent is a third-party agent that transfers Bootstrap A DHCP 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[RFC951] and residing on different subnets, per RFC 951 [RFC951] and RFC 1542
RFC1542[RFC1542]. [RFC1542].
o "DHCP server" o "DHCP server"
A DHCP server is an Internet host that returns configuration A DHCP server is an Internet host that returns configuration
parameters to DHCP clients. parameters to DHCP clients.
o "downstream" o "downstream"
Downstream is the direction from the access concentrator towards the Downstream is the direction from the access concentrator towards the
broadband subscriber. broadband subscriber.
skipping to change at page 7, line 8 skipping to change at page 7, line 8
low compared to fast path data transfer. low compared to fast path data transfer.
o "upstream" o "upstream"
Upstream is the direction from the broadband subscriber towards the Upstream is the direction from the broadband subscriber towards the
access concentrator. access concentrator.
3. Motivation 3. Motivation
Consider a typical access concentrator (e.g., DSLAM) working also as Consider a typical access concentrator (e.g., DSLAM) working also as
a DHCP relay agent. "Fast path" and "slow path" generally exist in a DHCP relay agent. A "Fast path" and a "slow path" generally exist
most networking boxes. Fast path processing is done in network in most networking boxes. Fast path processing is done in a network
processor or an ASIC (Application Specific Integrated Circuit). Slow processor or an ASIC (Application Specific Integrated Circuit). Slow
path processing is done in a normal processor. As much as possible, path processing is done in a normal processor. As much as possible,
regular data handling code should be in fast path. Slow path regular data handling code should be in the fast path. Slow path
processing should be reduced as it may become a bottleneck. processing should be reduced as it may become a bottleneck.
For an access concentrator having multiple access ports, multiple IP For an access concentrator having multiple access ports, multiple IP
addresses may be assigned using DHCP to a single port and the number addresses may be assigned using DHCP to a single port and the number
of clients on a port may be unknown. The access concentrator may of clients on a port may be unknown. The access concentrator may
also not know the network portions of the IP addresses that are also not know the network portions of the IP addresses that are
assigned to its DHCP clients. assigned to its DHCP clients.
The access concentrator gleans IP address or other information for The access concentrator gleans IP address or other information from
antispoofing and for other purposes from DHCP negotiations. The DHCP negotiations for antispoofing and other purposes. The
antispoofing itself is done in fast path. Access concentrator keeps antispoofing itself is done in fast path. Access concentrator keeps
track of only one list of IP addresses: list of IP addresses that are track of only one list of IP addresses: list of IP addresses that are
assigned by DHCP server. Traffic for all other IP addresses is assigned by DHCP server; upstream traffic from all other IP addresses
dropped. If client starts its data transfer after its DHCP is dropped. If a client starts its data transfer after its DHCP
negotiations are gleaned by access concentrator, no legitimate negotiations have been gleaned by the access concentrator, no
packets will be dropped because of antispoofing. In other words, legitimate packets will be dropped because of antispoofing. In other
antispoofing is effective (no legitimate packets are dropped and all words, antispoofing is effective (no legitimate packets are dropped
spoofed packets are dropped) and efficient (antispoofing is done in and all spoofed packets are dropped) and efficient (antispoofing is
fast path). The intention is to achieve similar effective and done in the fast path). The intention is to achieve similar
efficient antispoofing in the lease query scenario also when an effective and efficient antispoofing in the lease query scenario also
access concentrator loses its gleaned information (for example, when an access concentrator loses its gleaned information (for
because of reboot). example, because of a reboot).
After a deep analysis, we found that the three existing query types After a deep analysis, we found that the three existing query types
supported by RFC 4388[RFC4388] do not provide effective and efficient supported by RFC 4388[RFC4388] do not provide effective and efficient
antispoofing for the above scenario and a new mechanism is required. antispoofing for the above scenario and a new mechanism is required.
The existing query types The existing query types
o necessitate a data driven approach: the lease queries can only be o necessitate a data-driven approach: the lease queries can only be
done when access concentrator receives data. That results in done when the access concentrator receives data; that results in
increased outage time for clients. increased outage time for clients;
o result in excessive negative caching consuming lot of resources o result in excessive negative caching, consuming a lot of resources
under a spoofing attack. under a spoofing attack;
o result in antispoofing being done in slow path instead of fast o result in antispoofing being done in the slow path instead of the
path. fast path.
The deeper analysis, which led to the above conclusions, itself The deeper analysis, which led to the above conclusions, itself
appears as an Appendix to this document. appears as an Appendix to this document.
4. Design Goals 4. Design Goals
The goal of this document is to provide a lightweight mechanism for The goal of this document is to provide a lightweight mechanism for
access concentrator to retrieve lease information available in the an access concentrator to retrieve lease information available in the
DHCP server. The mechanism SHOULD also support an access DHCP server. The mechanism SHOULD also support an access
concentrator to retrieve consolidated lease information for a concentrator to retrieve consolidated lease information for a
connection/circuit. connection/circuit.
4.1. Information Acquisition before Data Starts 4.1. Information Acquisition before Data Starts
Existing data driven approach by RFC 4388 [RFC4388] means that the The existing data driven approach specified by RFC 4388 [RFC4388]
lease queries can only be done when access concentrator receives means that the lease queries can only be performed when the access
data. If an approach exists to initiate lease queries even before concentrator receives data. If there was an approach to initiate
the calls come up, then it will be more effective. For antispoofing, lease queries even before the calls come up, then that would be more
packets need to be dropped until it gets the lease information from effective. For antispoofing, packets need to be dropped until the
DHCP server. If access concentrator finishes the lease queries access concentrator gets the lease information from the DHCP server.
before it start receiving data, then there is no need to drop If the access concentrator finishes the lease queries before it
legitimate packets. So, effectively outage time may be reduced. The receives upstream data, then there is no need to drop legitimate
lease queries should help in retrieving lease information even before packets. So, effectively outage time may be reduced. The lease
the data starts flowing and should be independent of data traffic. queries should help in retrieving lease information even before the
data starts flowing and should be independent of data traffic.
4.2. Lessen Negative Caching 4.2. Reduce Negative Caching
If lease queries result in negative caches, then that puts additional If lease queries yield negative results that need to be cached, then
overhead on access concentrator. The negative caches not only that puts additional overhead on the access concentrator. Negative
consume precious resources they also need to be managed. Hence they caches not only consume precious resources but they also need to be
should be avoided as much as possible. The lease queries should managed. Hence they should be avoided as much as possible. The
reduce the need for negative caching as far as possible. lease queries should reduce the need for negative caching as far as
possible.
4.3. Antispoofing in 'Fast Path' 4.3. Antispoofing in 'Fast Path'
If Antispoofing is not done in fast path, it will become a bottleneck If antispoofing is not done in the fast path, it will become a
and may lead to denial of service of access concentrator. The lease bottleneck and may lead to denial of service of the access
queries should make it possible to do antispoofing in fast path. concentrator. The lease queries should make it possible to do
antispoofing in the fast path.
5. Protocol Overview 5. Protocol Overview
RFC 3046 [RFC3046] defines two sub-options for Relay Agent RFC 3046 [RFC3046] defines two sub-options for the Relay Agent
Information option. Sub-option 1 corresponds to circuit ID which Information option. Sub-option 1 corresponds to the circuit ID that
identifies the local circuit of the access concentrator. This sub- identifies the local circuit of the access concentrator. This sub-
option is unique to the relay agent. Sub-option 2 corresponds to option is unique to the relay agent. Sub-option 2 corresponds to the
remote ID which identifies the remote host end of the circuit. This remote ID that identifies the remote host end of the circuit. This
is globally unique in the network. is globally unique in the network.
This document defines a new query type based on remote ID sub-option. This document defines a new query type based on the remote ID sub-
Suppose that the access concentrator (e.g., DSLAM) lost the lease option. Suppose that the access concentrator (e.g., DSLAM) lost the
information when it was rebooted. When the access concentrator comes lease information when it was rebooted. When the access concentrator
up, it would initiate a DHCPLEASEQUERY message for each connection/ comes up, it would initiate (for each connection/circuit) a
circuit containing the Relay Agent Information option [RFC3046] with DHCPLEASEQUERY message containing the Relay Agent Information option
sub-option remote ID. DHCP server must return an IP address in the [RFC3046] with sub-option remote ID. The DHCP server must return an
ciaddr if it has any record of the client described by the remote ID. IP address in the ciaddr field if it has any record of the client
In the absence of specific configuration information to the contrary, described by the remote ID. In the absence of specific configuration
it SHOULD be the IP address with the latest client-last-transaction- information to the contrary, it SHOULD be the IP address with the
time associated with the client described by the remote ID. The DHCP latest client-last-transaction-time associated with the client
servers that implement this document always send a response described by the remote ID. The DHCP servers that implement this
(DHCPLEASEACTIVE or DHCPLEASEUNKNOWN) to the DHCPLEASEQUERY message. document always send a response ( DHCPLEASEACTIVE or
The reasons why a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN message might DHCPLEASEUNKNOWN) to the DHCPLEASEQUERY message. The reasons why a
be generated are explained in the specific query regimes below. DHCPLEASEACTIVE or DHCPLEASEUNKNOWN message is generated are
Servers that do not implement the DHCPLEASEQUERY based on remote ID explained in the specific query regimes below. Servers that do not
message SHOULD simply not respond. implement DHCPLEASEQUERY based on remote ID SHOULD simply not
respond.
The query regime is described below: The query regime is described below:
o Query by Agent Remote ID sub-option: o Query by Agent Remote ID sub-option:
For this query, the requester supplies only a option 82 which will For this query, the requester supplies in the DHCPLEASEQUERY message
include only an Agent Remote ID sub-option in the DHCPLEASEQUERY only an option 82 which will include only an Agent Remote ID sub-
message. The DHCP server will return any information that it has on option. The DHCP server will return any information that it has on
the IP address most recently accessed by a client with that Agent the IP address most recently accessed by a client with that Agent
Remote ID. In addition, it SHOULD supply any additional IP addresses Remote ID. In addition, it SHOULD supply any additional IP addresses
that have been associated with Agent Remote ID in different subnets. that have been associated with the Agent Remote ID in different
Information about these bindings can then be found using the Query by subnets. Information about these bindings can then be found using
IP Address, as described in RFC 4388[RFC4388]. the Query by IP Address, as described in RFC 4388 [RFC4388].
The DHCP server MUST reply with a DHCPLEASEACTIVE message if the The DHCP server MUST reply with a DHCPLEASEACTIVE message if the
Agent Remote ID in the DHCPLEASEQUERY message currently has an active Agent Remote ID in the DHCPLEASEQUERY message currently has an active
lease on an IP address in this DHCP server. Otherwise, the server lease on an IP address in this DHCP server. Otherwise, the server
MUST reply with a DHCPLEASEUNKNOWN message. MUST reply with a DHCPLEASEUNKNOWN message.
6. Protocol Details 6. Protocol Details
In this section, DHCPLEASEQUERY message refers to DHCPLEASEQUERY In this section, DHCPLEASEQUERY message refers to DHCPLEASEQUERY
message with query by remote ID. message with query by remote ID.
6.1. Sending the DHCPLEASEQUERY Message 6.1. Sending the DHCPLEASEQUERY Message
The DHCPLEASEQUERY message is typically sent by an access The DHCPLEASEQUERY message is typically sent by an access
concentrator. The DHCPLEASEQUERY message uses the DHCP message concentrator. The DHCPLEASEQUERY message uses the DHCP message
format as described in RFC2131[RFC2131], and uses message number 10 format as described in RFC2131 [RFC2131], and uses message number 10
in the DHCP Message Type option (option 53). The DHCPLEASEQUERY in the DHCP Message Type option (option 53). The DHCPLEASEQUERY
message has the following pertinent message contents: message has the following pertinent message contents:
o The giaddr MUST be set to the IP address of the requester (i.e., o The giaddr MUST be set to the IP address of the requester (i.e.,
the access concentrator). The giaddr is the return address of the the access concentrator). The giaddr is the return address of the
DHCPLEASEACTIVE or DHCPLEASEUNKNOWN message from the DHCP server. DHCPLEASEACTIVE or DHCPLEASEUNKNOWN message from the DHCP server.
Note that this use of the giaddr is consistent with the definition Note that this use of the giaddr is consistent with the definition
of giaddr in RFC2131[RFC2131], where the giaddr is always used as of giaddr in RFC2131 [RFC2131], where the giaddr is always used as
the return address of the DHCP response message. In some (but not the return address of the DHCP response message. In some (but not
all) contexts in RFC 2131, the address to allocate to a client is all) contexts in RFC 2131, the address to allocate to a client is
selected based on 'giaddr'. selected based on 'giaddr'.
o The Parameter Request List option (option 55) SHOULD be set to the o The Parameter Request List option (option 55) SHOULD be set to the
options of interest to the requester. It MUST include the Relay options of interest to the requester. It MUST include the Relay
Agent Information option (option 82). The other interesting Agent Information option (option 82). The other interesting
options are likely to include the IP Address Lease Time option options are likely to include the IP Address Lease Time option
(option 51), and possibly the Vendor class identifier option (option 51), and possibly the Vendor class identifier option
(option 60). In the absence of a Parameter Request List option, (option 60). In the absence of a Parameter Request List option,
the server SHOULD return the same options it would return for a the server SHOULD return the same options it would return for a
DHCPREQUEST message that didn't contain Parameter Request List DHCPREQUEST message that didn't contain a Parameter Request List
option (option 55), which includes those mandated by Section 4.3.1 option (option 55), which includes those mandated by Section 4.3.1
of [RFC2131] as well as any options that the server was configured of [RFC2131] as well as any options that the server was configured
to always return to a client. to always return to a client.
Additional details concerning different query types are Additional details concerning different query types are:
o Query by Agent Remote ID sub-option: o Query by Agent Remote ID sub-option:
* There MUST be a Relay Agent Information option (option 82) with * There MUST be a Relay Agent Information option (option 82) with
only Agent Remote ID sub-option (sub-option 2) in the only an Agent Remote ID sub-option (sub-option 2) in the
DHCPLEASEQUERY message. DHCPLEASEQUERY message.
* The "ciaddr" field MUST be set to zero. * The ciaddr field MUST be set to zero.
* The values of htype, hlen, and chaddr MUST be set to zero. * The values of htype, hlen, and chaddr MUST be set to zero.
* The Client-identifier option (option 61) MUST NOT appear in the * The Client-identifier option (option 61) MUST NOT appear in the
packet. packet.
The DHCPLEASEQUERY message SHOULD be sent to a DHCP server which is The DHCPLEASEQUERY message SHOULD be sent to a DHCP server which is
known to possess authoritative information concerning the remote ID. known to possess authoritative information concerning the remote ID.
The DHCPLEASEQUERY message MAY be sent to more than one DHCP server, The DHCPLEASEQUERY message MAY be sent to more than one DHCP server,
and in the absence of information concerning which DHCP server might and in the absence of information concerning which DHCP server might
possess authoritative information concerning the remote ID, it SHOULD possess authoritative information concerning the remote ID, it SHOULD
be sent to all DHCP servers configured for the associated relay agent be sent to all DHCP servers configured for the associated relay agent
(if any are known). (if any are known).
6.2. Receiving the DHCPLEASEQUERY Message 6.2. Receiving the DHCPLEASEQUERY Message
A DHCPLEASEQUERY message MUST have a non-zero giaddr. The A DHCPLEASEQUERY message MUST have a non-zero giaddr. The
DHCPLEASEQUERY message MUST have a zero ciaddr, a zero htype/hlen/ DHCPLEASEQUERY message MUST have a zero ciaddr, a zero htype/hlen/
chaddr, and no Client-identifier option. The DHCPLEASEQUERY message chaddr, and no Client-identifier option. The DHCPLEASEQUERY message
MUST have a relay agent option 82 with only remote ID sub-option. MUST have a relay agent option 82 with only a remote ID sub-option.
6.3. Responding to the DHCPLEASEQUERY Message 6.3. Responding to the DHCPLEASEQUERY Message
There are two possible responses to a DHCPLEASEQUERY message: There are two possible responses to a DHCPLEASEQUERY message:
o DHCPLEASEUNKNOWN o DHCPLEASEUNKNOWN
The DHCPLEASEUNKNOWN message indicates that the client specified in The DHCPLEASEUNKNOWN message indicates that the client specified in
the DHCPLEASEQUERY message is not allocated any lease or it is not the DHCPLEASEQUERY message is not allocated any lease or it is not
managed by the server. managed by the server.
o DHCPLEASEACTIVE o DHCPLEASEACTIVE
The DHCPLEASEACTIVE message indicates that the server not only knows The DHCPLEASEACTIVE message indicates that the server not only knows
the client specified in the DHCPLEASEQUERY message, but also knows the client specified in the DHCPLEASEQUERY message, but also knows
that there is an active lease for that client. that there is an active lease for that client.
6.4. Determining the IP address to be used in response 6.4. Determining the IP address to be used in the response
Since the response to a DHCPLEASEQUERY request can only contain full Since the response to a DHCPLEASEQUERY request can only contain full
information about one IP address -- the one that appears in the information about one IP address -- the one that appears in the
"ciaddr" field -- determination of which IP address about which to ciaddr field -- determination of the IP address about which to
respond is a key issue. Of course, the values of additional IP respond is a key issue. Of course, the values of additional IP
addresses for which a client has a lease must also be returned in the addresses for which a client has a lease must also be returned in the
associated-ip option (RFC 4388[RFC4388], Section 6.1, #3). This is associated-ip option (RFC 4388 [RFC4388], Section 6.1, #3). This is
the only information returned not directly associated with the IP the only information returned not directly associated with the IP
address in the "ciaddr" field. address in the ciaddr field.
The client's identity is any client that has proffered an identical
Agent Remote ID (if the option 82 with Agent Remote ID sub-option
appears in DHCPLEASEQUERY message). This client matching approach
will, for the purposes of this section, be described as "remote ID".
The IP address placed in the "ciaddr" field of a DHCPLEASEACTIVE The IP address placed in the ciaddr field of a DHCPLEASEACTIVE
message MUST be the IP address with the latest client-last- message MUST be the IP address with the latest client-last-
transaction-time associated with the client described by the remote transaction-time associated with the client described by the remote
ID specified in the DHCPLEASEQUERY message. ID specified in the DHCPLEASEQUERY message.
If there is only a single IP address that fulfills this criteria, If there is only a single IP address that fulfils this criteria, then
then it MUST be placed in the "ciaddr" field of the DHCPLEASEACTIVE it MUST be placed in the ciaddr field of the DHCPLEASEACTIVE message.
message.
In the case where more than one IP address has been accessed by the In the case where more than one IP address has been accessed by the
client specified by the Remote ID, then the DHCP server MUST return client specified by the Remote ID, then the DHCP server MUST return
the IP address returned to the client in the most recent transaction the IP address returned to the client in the most recent transaction
with the client unless the DHCP server has been configured by the with the client unless the DHCP server has been configured by the
server administrator to use some other preference mechanism. server administrator to use some other preference mechanism.
6.5. Building a DHCPLEASEUNKNOWN or DHCPLEASEACTIVE Messages 6.5. Building a DHCPLEASEUNKNOWN or DHCPLEASEACTIVE Message
For a DHCPLEASEUNKNOWN message, DHCP server MUST echo the received In a DHCPLEASEUNKNOWN response message, the DHCP server MUST echo the
Option 82 available in DHCPLEASEQUERY in the response. No other Option 82 received in the DHCPLEASEQUERY message. No other options
options are returned for this message. With that the processing for are returned for these messages. With that the processing for a
a DHCPLEASEUNKNOWN message is complete. DHCPLEASEUNKNOWN message is complete.
For the DHCPLEASEACTIVE message, the rest of the processing largely For the DHCPLEASEACTIVE message, the rest of the processing largely
involves returning information about the IP address specified in the involves returning information about the IP address specified in the
"ciaddr" field. ciaddr field.
The MAC address of the DHCPLEASEACTIVE message MUST be set to the The MAC address of the DHCPLEASEACTIVE message MUST be set to the
values that identify the client associated with the IP address in the values that identify the client associated with the IP address in the
"ciaddr" field of the DHCPLEASEACTIVE message. ciaddr field of the DHCPLEASEACTIVE message.
If the Client-identifier option (option 61) is specified in the If the Client-identifier option (option 61) is specified in the
Parameter Request List option (option 55), then the Client-identifier Parameter Request List option (option 55), then the Client-identifier
(if any) of the client associated with the IP address in the "ciaddr" (if any) of the client associated with the IP address in the ciaddr
field SHOULD be returned in the DHCPLEASEACTIVE message. field SHOULD be returned in the DHCPLEASEACTIVE message.
In the case where more than one IP address has been involved in a In the case where more than one IP address has been involved in a
DHCP message exchange with the client specified by the Agent Remote DHCP message exchange with the client specified by the Agent Remote
ID, then the list of all those IP addresses MUST be returned in the ID, then the list of all those IP addresses MUST be returned in the
associated-ip option, whether or not that option was requested as associated-ip option, whether or not that option was requested as
part of the Parameter Request List option. part of the Parameter Request List option.
If the IP Address Lease Time option (option 51) is specified in the If the IP Address Lease Time option (option 51) is specified in the
Parameter Request List then the DHCP server MUST return this option Parameter Request List then the DHCP server MUST return this option
in the DHCPLEASEACTIVE message with its value equal to the time in the DHCPLEASEACTIVE message with its value equal to the time
remaining until lease expiration. remaining until lease expiration.
A request for the Renewal (T1) Time Value option or the Rebinding A request for the Renewal (T1) Time Value option or the Rebinding
(T2) Time Value option in the Parameter Request List of the (T2) Time Value option in the Parameter Request List of the
DHCPLEASEQUERY message MUST be handled like the IP Address Lease Time DHCPLEASEQUERY message MUST be handled like the IP Address Lease Time
option is handled. DHCP server SHOULD return these options (when option is handled. The DHCP server SHOULD return these options (when
requested) with the remaining time until renewal or rebinding, requested) with the remaining time until renewal or rebinding,
respectively. respectively.
The information contained in the most recent Relay Agent Information The information contained in the most recent Relay Agent Information
option received from the relay agent associated with this IP address option received from the relay agent associated with this IP address
MUST be included in the DHCPLEASEACTIVE message. MUST be included in the DHCPLEASEACTIVE message.
The DHCPLEASEACTIVE message SHOULD include the values of all other The DHCPLEASEACTIVE message SHOULD include the values of all other
options not specifically discussed above that were requested in the options not specifically discussed above that were requested in the
Parameter Request List of the DHCPLEASEQUERY message and that are Parameter Request List of the DHCPLEASEQUERY message and that are
skipping to change at page 15, line 28 skipping to change at page 15, line 22
Information option information included in the packet to refresh its Information option information included in the packet to refresh its
location information for this IP address. An access concentrator is location information for this IP address. An access concentrator is
likely to query by IP address for all the IP addresses specified in likely to query by IP address for all the IP addresses specified in
the associated-ip option in the response, if any, at this point in the associated-ip option in the response, if any, at this point in
time. time.
When a DHCPLEASEUNKNOWN message is received by an access concentrator When a DHCPLEASEUNKNOWN message is received by an access concentrator
that had sent out a DHCPLEASEQUERY message, it means that the DHCP that had sent out a DHCPLEASEQUERY message, it means that the DHCP
server does not have definitive information concerning the DHCP server does not have definitive information concerning the DHCP
client specified in the Agent Remote ID sub-option of the client specified in the Agent Remote ID sub-option of the
DHCPLEASEQUERY message. The access concentrator MAY store this DHCPLEASEQUERY message. The Access Concentrator MAY store this
information for future use. However, a DHCPLEASEQUERY SHOULD NOT be information for future use. However, a DHCPLEASEQUERY SHOULD NOT be
attempted with the same Remote ID su-option. attempted with the same Remote ID sub-option.
For leasequry by remote-id, the impact of negative caching is greatly For leasequery by remote-id, the impact of negative caching is
reduced as the the response leads to "definitive" information on all greatly reduced as the response leads to "definitive" information on
the hosts connected behind the connection. Note that in the case of all the hosts connected behind the connection. Note that in the case
RFC 4388 [RFC4388], a host spoofing several IP addresses can lead to of data-driven approach, a host spoofing several IP addresses can
negative caching of greater magnitude. Another important change this lead to negative caching of greater magnitude. Another important
draft brings is the removal of "periodic" leasequeries generated from change this draft brings is the removal of "periodic" leasequeries
negative caching caused by DHCPLEASEUNKNOWN. Since the information generated from negative caching caused by DHCPLEASEUNKNOWN. Since
obtained through query by remote-id is complete, there is no need of the information obtained through query by remote-id is complete,
attempting leasequery again for the same remote-id. there is no need of attempting leasequery again for the same
connection.
6.8. Receiving No Response to the DHCPLEASEQUERY Message 6.8. Receiving No Response to the DHCPLEASEQUERY Message
When an access concentrator receives no response to a DHCPLEASEQUERY When an access concentrator receives no response to a DHCPLEASEQUERY
message, it should be handled in the same manner as suggested in RFC message, it should be handled in the same manner as suggested in RFC
4388 [RFC4388]. 4388 [RFC4388].
6.9. Lease Binding Data Storage Requirements 6.9. Lease Binding Data Storage Requirements
IMPLEMENTATION: Implementation Note:
To generate replies for a lease query by remote-id effeciently, a To generate replies for a lease query by remote-id efficiently, a
DHCP server should index the lease binding data structures using DHCP server should index the lease binding data structures using
remote-id. remote-id.
6.10. Using the DHCPLEASEQUERY Message with Multiple DHCP Servers 6.10. Using the DHCPLEASEQUERY Message with Multiple DHCP Servers
This scenario should be handled in the same way it is done in RFC This scenario should be handled in the same way it is done in RFC
4388 [RFC4388]. 4388 [RFC4388].
7. RFC 4388 Considerations 7. RFC 4388 Considerations
This document is compatible with RFC 4388 [RFC4388] based This document is compatible with RFC 4388 [RFC4388] based
implementations which means that a client which supports this implementations, which means that a client that supports this
extension can work with a server not supporting this document extension can work with a server not supporting this document,
provided it uses RFC 4388 [RFC4388] defined query types. Also, a provided it uses RFC 4388 [RFC4388] defined query types. Also, a
server supporting this document can work with a client not supporting server supporting this document can work with a client not supporting
this query type. However, there are some changes that this document this query type. However, there are some changes that this document
proposes with respect to RFC 4388 [RFC4388]. Implementors extending proposes with respect to RFC 4388 [RFC4388]. Implementers extending
RFC 4388 [RFC4388] implementation to support this document, should RFC 4388 [RFC4388] implementations to support this document, should
take note of the following points: take note of the following points:
o RFC 4388 [RFC4388] suggests that a DHCPLEASEUNASSIGNED is returned o RFC 4388 [RFC4388] suggests that a DHCPLEASEUNASSIGNED is returned
only in the case of 'query by IP address'. All other query types only in the case of 'query by IP address'. All other query types
will have a return message of either DHCPLEASEACTIVE or will have a return message of either DHCPLEASEACTIVE or
DHCPLEASEUNKNOWN'. Although it is possible to return DHCPLEASEUNKNOWN. Although it would be possible to return
DHCPLEASEUNASSIGNED in case of a query by remote-id, in order to DHCPLEASEUNASSIGNED in case of a query by remote-id, in order to
maintain compatibility with other similar query types (MAC and maintain compatibility with other similar query types (MAC and
Client-id) a query by remote-id does not support a Client-id) a query by remote-id does not support a
DHCPLEASEUNASSIGNED response. DHCPLEASEUNASSIGNED response.
o There may be cases where a query by IP address/MAC address/Client o There may be cases where a query by IP address/MAC address/Client
Identifier has an option 82 containing remote ID. In that case, Identifier has an option 82 containing remote ID. In that case,
the query will still be recognized as query by IP address/MAC the query will still be recognized as query by IP address/MAC
address/Client Identifier as specified by RFC 4388 [RFC4388]. address/Client Identifier as specified by RFC 4388 [RFC4388].
skipping to change at page 19, line 8 skipping to change at page 19, line 8
8. Security Considerations 8. Security Considerations
This document does not introduce any new security concerns beyond This document does not introduce any new security concerns beyond
those specified in the original leasequery protocol RFC 4388 those specified in the original leasequery protocol RFC 4388
[RFC4388] specifications. [RFC4388] specifications.
9. IANA Considerations 9. 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. manage and does not request any new code point allocation. [[ RFC-
Editor: Please remove this section before publication. ]]
10. Acknowledgments 10. Acknowledgements
Copious amounts of text in this document are derived from RFC 4388 Copious amounts of text in this document are derived from RFC 4388
[RFC4388]. Kim kinnear provided valuable feedback on this document. [RFC4388]. Kim kinnear, Damien Neil, Stephen Jacob and Alfred Hoenes
provided valuable feedback on this document.
11. References 11. References
11.1. Normative Reference 11.1. Normative Reference
[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.
[RFC4388] Woundy, R. and K. Kinnear, "Dynamic Host Configuration [RFC4388] Woundy, R. and K. Kinnear, "Dynamic Host Configuration
Protocol (DHCP) Leasequery", RFC 4388, February 2006. Protocol (DHCP) Leasequery", RFC 4388, February 2006.
skipping to change at page 22, line 12 skipping to change at page 22, line 12
[RFC2132] Droms, R. and S. Alexander, "DHCP Options and BOOTP Vendor [RFC2132] Droms, R. and S. Alexander, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997. Extensions", RFC 2132, March 1997.
Appendix A. Why a New Leasequery is Required? Appendix A. Why a New Leasequery is Required?
The three existing query types supported by RFC 4388 do not provide The three existing query types supported by RFC 4388 do not provide
effective and efficient antispoofing for the above scenario. effective and efficient antispoofing for the above scenario.
o Query by Client Identifier o Query by Client Identifier
Query by Client Identifier is not possible because to use that access Query by Client Identifier is not possible because to use that, an
concentrator need to glean client identifier also but the whole issue access concentrator needs to glean the client identifier also, but
is that we need leasequeries because the gleaned information was the whole issue is that we need leasequeries because the gleaned
lost. On the other hand, we can query by client identifier when information was lost. On the other hand, we can query by client
client sends a DHCP request, but then there may not be any need for identifier when a client sends a DHCP request, but then there may not
lease query as such -- regular gleaning may be enough. be any need for lease query as such -- regular gleaning may be
enough.
o Query by IP Address o Query by IP Address
RFC 4388 suggests that it is preferable to use Query by IP Address RFC 4388 suggests that it is preferable to use Query by IP Address
when getting downstream traffic. when getting downstream traffic.
Query by IP address is not very useful in downstream traffic because Query by IP address is not very useful in downstream traffic because
downstream traffic may not exist for the clients on a access port. downstream traffic may not exist for the clients on a access port.
(In most Internet applications, downstream traffic exists only when a (In most Internet applications, downstream traffic exists only when a
client sends upstream traffic). In other words, the client will be client sends upstream traffic). In other words, the client will be
skipping to change at page 22, line 39 skipping to change at page 22, line 40
come. come.
Query by IP address may be used for upstream traffic. Then whenever Query by IP address may be used for upstream traffic. Then whenever
an upstream packet comes whose IP address is unknown to the access an upstream packet comes whose IP address is unknown to the access
concentrator, a lease query may be initiated. A related question is concentrator, a lease query may be initiated. A related question is
what to do with that upstream traffic itself until lease query what to do with that upstream traffic itself until lease query
response comes? If the traffic is dropped, we may be dropping response comes? If the traffic is dropped, we may be dropping
legitimate traffic. If the traffic is forwarded, we may be legitimate traffic. If the traffic is forwarded, we may be
forwarding spoofed packets. Once the lease response comes, forwarding spoofed packets. Once the lease response comes,
subsequent traffic is handled depending on the response. If a subsequent traffic is handled depending on the response. If a
DHCPLEASEACTIVE response comes, access concentrator will accept the DHCPLEASEACTIVE response arrives, the access concentrator will accept
traffic. If a DHCPLEASEUNASSIGNED response comes, access the traffic. If a DHCPLEASEUNASSIGNED response arrives, the access
concentrator will drop the traffic corresponding to the IP address. concentrator will drop the traffic corresponding to the IP address.
If a DHCPLEASEUNKNOWN response comes, access concentrator may drop If a DHCPLEASEUNKNOWN response arrives, the access concentrator may
the traffic corresponding to the IP address but will have to drop the traffic corresponding to the IP address but will have to
periodically send the lease query for that IP address again periodically send the lease query for that IP address again
(additional overhead). The process is triggered whenever an unknown (additional overhead). The process is triggered whenever an unknown
IP address comes. IP address comes.
Note that access concentrator needs to keep track of 4 lists of IP Note that the access concentrator needs to keep track of 4 lists of
addresses: (1) List of IP addresses for which it got DHCPLEASEACTIVE IP addresses: (1) List of IP addresses for which it got
responses; (2) List of IP addresses for which it got DHCPLEASEACTIVE responses; (2) List of IP addresses for which it got
DHCPLEASEUNASSIGNED responses; (3) List of IP addresses for which it DHCPLEASEUNASSIGNED responses; (3) List of IP addresses for which it
got DHCPLEASEUNKNOWN responses; (4) All other IP addresses. got DHCPLEASEUNKNOWN responses; (4) All other IP addresses.
This approach may be acceptable if only legitimate traffic is This approach may be acceptable if only legitimate traffic is
received. Consider the case when someone sends packets that uses received. Consider however the case when someone sends packets that
spoofed IP addresses. In that case, lease response will be use spoofed IP addresses. In that case, the lease response will be
DHCPLEASEUNASSIGNED or DHCPLEASEUNKNOWN. RFC 4388 suggests usage of DHCPLEASEUNASSIGNED or DHCPLEASEUNKNOWN. RFC 4388 suggests usage of
negative caching in this regard (which involves additional negative caching in this regard (which involves additional
resources). resources).
In a spoofing type of attack, negative caching information may grow In a spoofing type of attack, negative caching information may grow
considerably if attacker varies the source IP address. For each such considerably if the attacker varies the source IP address. For each
new source IP address, traffic will come to slow path, a new lease such new source IP address, traffic will come to the slow path, a new
query needs to be initiated, response will be processed, and negative lease query needs to be initiated, the response will be processed,
caching to be done. That will mean using many resources for negative and negative caching needs to be done. That means using many
caching. resources for negative caching.
RFC 4388 suggests that if the access concentrator knows the network RFC 4388 suggests that if the access concentrator knows the network
portion of the IP addresses that are assigned to its clients, then portion of the IP addresses that are assigned to its clients, then
some amount of antispoofing can be done in fast path and some lease some amount of antispoofing can be done in the fast path and some
queries may be avoided. But as indicated before, that information lease queries may be avoided. But as indicated above, that
may not always be available to access concentrators. information may not always be available to access concentrators.
Effectively, antispoofing support involves considerable slow path Effectively, antispoofing support involves considerable slow path
processing and considerable resources tied for negative caching. processing and considerable resources tied for negative caching.
RFC 4388 says that DHCP server should be protected from being flooded RFC 4388 says that DHCP servers should be protected from being
with too many leasequery requests and access concentrator also should flooded with too many leasequery requests and access concentrators
not send too many lease query messages at a time. This would mean also should not send too many lease query messages at a time. This
that legitimate clients may be excessively delayed getting their would mean that legitimate clients may be excessively delayed getting
information in the face of antispoofing attacks. their information in the face of spoofing attacks.
It is concluded that antispoofing is neither effective nor efficient It is concluded that antispoofing is neither effective nor efficient
with this query type. with this query type.
o Query by MAC Address o Query by MAC Address
Query by MAC address can also be used similar to query by IP address Query by MAC address can also be used similar to query by IP address
described above. Indeed, query by MAC address may be better than described above. Indeed, query by MAC address may be better than
query by IP address in one sense because of the possible presence of query by IP address in one sense because of the possible presence of
associated-ip option in lease responses (Note that associated-ip an associated-ip option in lease responses. (Note that an
option does not appear in responses for query by IP address). With associated-ip option does not appear in responses for query by IP
associated-ip option, access concentrator can get information not address.) With associated-ip option, the access concentrator can get
only about the IP address/MAC address that triggered the lease query information not only about the IP address/MAC address that triggered
but also about other IP addresses that are associated with the the lease query but also about other IP addresses that are associated
original MAC address. That way, when traffic that uses the other IP with the original MAC address. That way, when traffic that uses the
addresses comes along, access concentrator is already prepared to other IP addresses comes along, the access concentrator is already
deal with them. prepared to deal with them.
Although, query by MAC address is better than query by IP address in Although query by MAC address is better than query by IP address in
the above respect, it has a specific problem which is not shared by the above respect, it has a specific problem which is not shared by
query by IP address. For a query by MAC address, only two types of query by IP address. For a query by MAC address, only two types of
responses are possible: DHCPLEASEUNKNOWN and DHCPLEASEACTIVE; responses are possible: DHCPLEASEUNKNOWN and DHCPLEASEACTIVE;
DHCPLEASEUNASSIGNED is not supported. This is particularly DHCPLEASEUNASSIGNED is not supported. This is particularly
troublesome when a DHCP server indeed has definitive information that troublesome when a DHCP server indeed has definitive information that
no IP addresses are associated with the specified MAC address in the no IP addresses are associated with the specified MAC address in the
leasequery, but it is forced to respond with DHCPLEASEUNKNOWN instead leasequery, but it is forced to respond with DHCPLEASEUNKNOWN instead
of DHCPLEASEUNASSIGNED. As we have seen above, unlike of DHCPLEASEUNASSIGNED. As we have seen above, unlike
DHCPLEASEUNASSIGNED, DHCPLEASEUNKNOWN requires periodic querying with DHCPLEASEUNASSIGNED, DHCPLEASEUNKNOWN requires periodic querying the
DHCP server, an additional overhead. DHCP server, an additional overhead.
Moreover, query by MAC address also shares all other issues we Moreover, query by MAC address also shares all other issues we
discussed above for query by IP address. discussed above for query by IP address.
We conclude that existing lease query types are not appropriate to We conclude that existing lease query types are not appropriate to
achieve effective and efficient antispoofing. achieve effective and efficient antispoofing.
Authors' Addresses Authors' Addresses
Pavan Kurapati Pavan Kurapati
Infosys Technologies Ltd.
44 Electronics City, Hosur Road
Bangalore 560 100
India
Email: pavan_kurapati@infosys.com Email: pavan.kurapati@gmail.com
URI: http://www.infosys.com/
D.T.V Ramakrishna Rao D.T.V Ramakrishna Rao
Infosys Technologies Ltd. Infosys Technologies Ltd.
44 Electronics City, Hosur Road 44 Electronics City, Hosur Road
Bangalore 560 100 Bangalore 560 100
India India
Email: ramakrishnadtv@infosys.com Email: ramakrishnadtv@infosys.com
URI: http://www.infosys.com/ URI: http://www.infosys.com/
 End of changes. 73 change blocks. 
217 lines changed or deleted 219 lines changed or added

This html diff was produced by rfcdiff 1.37a. The latest version is available from http://tools.ietf.org/tools/rfcdiff/