DHC Working Group P. Kurapati
Internet-Draft Juniper Networks Ltd.
Expires: February 7, 2011 R. Desetti
B. Joshi
Infosys Technologies Ltd.
August 6, 2010
DHCPv4 Leasequery by Relay Agent Remote ID
draft-ietf-dhc-leasequery-by-remote-id-06.txt
Abstract
Some Relay Agents extract lease information from the DHCP messages
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
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 7, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Kurapati, et al. Expires February 7, 2011 [Page 1]
Internet-Draft Query by Remote ID August 2010
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Sending the DHCPLEASEQUERY Message . . . . . . . . . . . . 8
4.2. Responding to the DHCPLEASEQUERY Message . . . . . . . . . 9
4.3. Building a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN message . . 9
4.4. Determining the IP address to be used in response . . . . 10
4.5. Sending a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message . . 10
4.6. Receiving a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN
Message . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.7. Receiving No Response to the DHCPLEASEQUERY Message . . . 11
4.8. Lease Binding Data Storage Requirements . . . . . . . . . 11
4.9. Using the DHCPLEASEQUERY Message with Multiple DHCP
Servers . . . . . . . . . . . . . . . . . . . . . . . . . 11
5. RFC 4388 Considerations . . . . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.1. Normative Reference . . . . . . . . . . . . . . . . . . . 16
9.2. Informative Reference . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
Kurapati, et al. Expires February 7, 2011 [Page 2]
Internet-Draft Query by Remote ID August 2010
1. Introduction
DHCP relay agents snoop DHCP messages and append a relay agent
information option before relaying them to the configured DHCP
Server. In this process, some relay agents also glean the lease
information sent by the server and maintain this locally. This
information is used to prevent spoofing attempts from clients and
also sometimes to install routing information. When a relay agent
reboots, this information is lost. RFC 4388 [RFC4388] has defined a
mechanism to retrieve this lease information from the DHCP server.
The existing query types defined by RFC 4388 [RFC4388] are data-
driven. When a client sends data upstream, the relay agent can query
the server about the related lease information, based on the source
MAC/IP address. These mechanisms do not scale well when there are
thousands of clients connected to the relay agent. In the data-
driven model, DHCP Leasequery does not provide the full, consolidated
active Lease informations associated with a given connection/circuit
which will result in inefficient anti-spoofing. The relay agent also
has to contend with considerable resources for negative caching
specially under spoofing attacks.
We need a mechanism for a relay agent to retrieve the consolidated
lease information for a given connection/circuit before upstream
traffic is sent by the clients.
+--------+
| DHCP | +--------------+
| Server |-...-| DSLAM |
| | | Relay Agent |
+--------+ +--------------+
| |
+------+ +------+
|Modem1| |Modem2|
+------+ +------+
| | |
+-----+ +-----+ +-----+
|Host1| |Host2| |Host3|
+-----+ +-----+ +-----+
Figure 1
For example, when a DSLAM acting as a Relay Agent is rebooted, it
should query the server for the lease information for all the
connections/circuits. Also, as shown in the above figure, there
could be multiple clients on one DSL circuit. The relay agent should
get the lease information of all the clients connected to a DSL
circuit. This is possible by introducing a new query type based on
the Remote ID sub-option of the Relay Agent Information option. This
Kurapati, et al. Expires February 7, 2011 [Page 3]
Internet-Draft Query by Remote ID August 2010
document talks about the motivation for the new query type and the
method to perform it.
Kurapati, et al. Expires February 7, 2011 [Page 4]
Internet-Draft Query by Remote ID August 2010
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
This document uses the following terms:
o "Access Concentrator"
An access concentrator is a router or switch at the broadband access
provider's edge of a public broadband access network. This document
assumes that the access concentrator includes the DHCP relay agent
functionality.
o "DHCP client"
A DHCP client is an Internet host using DHCP to obtain configuration
parameters such as a network address.
o "DHCP relay agent"
A DHCP relay agent is a third-party agent that transfers Bootstrap
Protocol (BOOTP) and DHCP messages between clients and servers
residing on different subnets, per RFC 951 [RFC951] and RFC 1542
[RFC1542].
o "DHCP server"
A DHCP server is an Internet host that returns configuration
parameters to DHCP clients.
o "Fast path"
Data transfer which happens through Network Processor or an ASIC
which are programmed to forward the data at very high speeds.
o "Gleaning"
Gleaning is the extraction of location information from DHCP
messages, as the messages are forwarded by the DHCP relay agent
function.
o "Location information"
Location information is information needed by the access concentrator
to forward traffic to a broadband-accessible host. This information
includes knowledge of the host hardware address, the port or virtual
Kurapati, et al. Expires February 7, 2011 [Page 5]
Internet-Draft Query by Remote ID August 2010
circuit that leads to the host, and/or the hardware address of the
intervening subscriber modem.
o "MAC address"
In the context of a DHCP packet, a MAC address consists of the
following fields: hardware type "htype", hardware length "hlen", and
client hardware address "chaddr".
o "Slow path"
Data transfer which happens through the control plane. Typically
this has very limited buffers to store data and the speeds are very
low compared to fast path data transfer.
o "Upstream"
Upstream is the direction from the broadband subscriber towards the
access concentrator.
Kurapati, et al. Expires February 7, 2011 [Page 6]
Internet-Draft Query by Remote ID August 2010
3. Motivation
Consider a typical access concentrator (e.g., DSLAM) working also as
a DHCP relay agent. A "Fast path" and a "slow path" generally exist
in most networking boxes. Fast path processing is done in a network
processor or an ASIC (Application Specific Integrated Circuit). Slow
path processing is done in a normal processor. As much as possible,
regular data forwarding should be done in the fast path. Slow path
processing should be reduced as it may become a bottleneck.
For an access concentrator having multiple access ports, multiple IP
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
also not know the network portions of the IP addresses that are
assigned to its DHCP clients.
The access concentrator gleans IP address or other information from
DHCP negotiations for antispoofing and other purposes. The
antispoofing itself is done in fast path. Access concentrator keeps
track of only one list of IP addresses: list of IP addresses that are
assigned by DHCP server; upstream traffic from all other IP addresses
is dropped. If a client starts its data transfer after its DHCP
negotiations have been gleaned by the access concentrator, no
legitimate packets will be dropped because of antispoofing. In other
words, antispoofing is effective (no legitimate packets are dropped
and all spoofed packets are dropped) and efficient (antispoofing is
done in the fast path). The intention is to achieve similar
effective and efficient antispoofing in the lease query scenario also
when an access concentrator loses its gleaned information (for
example, because of a reboot).
After a deep analysis, we found that the three existing query types
supported by RFC 4388 [RFC4388] do not provide effective and
efficient antispoofing for the above scenario and a new mechanism is
required.
The existing query types
o necessitate a data-driven approach: the lease queries can only be
done when the access concentrator receives data. This results in
increased outage time for clients
o results in excessive negative caching, consuming a lot of
resources under a spoofing attack
o results in antispoofing being done in the slow path instead of the
fast path
Kurapati, et al. Expires February 7, 2011 [Page 7]
Internet-Draft Query by Remote ID August 2010
4. Protocol Details
This section talks about the protocol details for query by Remote ID.
Most of the message handlings are similar to RFC 4388 [RFC4388] and
this section highlights only the differences. Reader is advised to
go through RFC 4388 [RFC4388] before going through this section for
complete understanding of the protocol.
A DHCPLEASEQUERY specified in this document specifies a lease query
by Remote ID unless otherwise specified.
RFC 3046 [RFC3046] defines two sub-options for the Relay Agent
Information option. Sub-option 1 corresponds to the Circuit ID that
identifies the local circuit of the access concentrator. This sub-
option is unique to the relay agent. Sub-option 2 corresponds to the
Remote ID that identifies the remote host end of the circuit. This
is globally unique in the network.
This document defines a new query type based on the Remote ID sub-
option. Suppose that the access concentrator (e.g., DSLAM) lost the
lease information when it was rebooted. When the access concentrator
comes up, it would initiate (for each connection/circuit) a dhcp
lease query by Remote ID as defined in this section. For this query,
the requester supplies only an option 82 which will include only a
Remote ID sub-option in the DHCPLEASEQUERY message.
The DHCP server MUST reply with a DHCPLEASEACTIVE message if there is
an active lease corresponding to the Remote ID that is present in the
DHCPLEASEQUERY message. Otherwise, the server MUST reply with a
DHCPLEASEUNKNOWN message. Servers that do not implement
DHCPLEASEQUERY based on Remote ID SHOULD simply not respond.
4.1. Sending the DHCPLEASEQUERY Message
The DHCPLEASEQUERY message is typically sent by an access
concentrator. The DHCPLEASEQUERY message uses the DHCP message
format as described in RFC 2131 [RFC2131], and uses message number 10
in the DHCP Message Type option (option 53). The DHCPLEASEQUERY
message has the following pertinent message contents:
o The giaddr and Parameter Request List option are set as explained
in section 6.2 of RFC 4388 [RFC4388].
o There MUST be a Relay Agent Information option (option 82) with
only a Remote ID sub-option (sub-option 2) in the DHCPLEASEQUERY
message.
Kurapati, et al. Expires February 7, 2011 [Page 8]
Internet-Draft Query by Remote ID August 2010
o The ciaddr field MUST be set to zero.
o The values of htype, hlen, and chaddr MUST be set to zero.
o The Client Identifier option (option 61) MUST NOT appear in the
packet.
The DHCPLEASEQUERY message SHOULD be sent to a DHCP server which is
known to possess authoritative information concerning the Remote ID.
The DHCPLEASEQUERY message MAY be sent to more than one DHCP server,
and in the absence of information concerning which DHCP server might
possess authoritative information concerning the Remote ID, it SHOULD
be sent to all DHCP servers configured for the associated relay agent
(if any are known).
4.2. Responding to the DHCPLEASEQUERY Message
There are two possible responses to a DHCPLEASEQUERY message:
o DHCPLEASEUNKNOWN
The DHCPLEASEUNKNOWN message indicates that the client associated
with the Remote ID suboption of the DHCPLEASEQUERY message is not
allocated any lease or it is not managed by the server.
o DHCPLEASEACTIVE
The DHCPLEASEACTIVE message indicates that the server not only knows
the client specified in the DHCPLEASEQUERY message, but also knows
that there is an active lease for that client.
4.3. Building a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN message
A DHCPLEASEACTIVE message is built by populating information
pertaining to the client associated with the IP address specified in
the ciaddr field.
In the case where more than one IP address has been involved in a
DHCP message exchange with the client specified by the Remote 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
part of the Parameter Request List option.
In a DHCPLEASEUNKNOWN response message, the DHCP server MUST echo the
Option 82 received in the DHCPLEASEQUERY message. No other options
are returned for these messages.
For all other options that are specified in Parameter Request List,
Kurapati, et al. Expires February 7, 2011 [Page 9]
Internet-Draft Query by Remote ID August 2010
the processing is same as mentioned in section 6.4.2 of RFC 4388
[RFC4388].
4.4. Determining the IP address to be used in response
The IP address placed in the ciaddr field of a DHCPLEASEACTIVE
message MUST be the IP address with the latest client-last-
transaction-time associated with the client described by the Remote
ID specified in the DHCPLEASEQUERY message.
If there is only a single IP address that fulfills this criteria,
then it MUST be placed in the ciaddr field of the DHCPLEASEACTIVE
message.
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
the IP address returned to the client in the most recent transaction
with the client unless the DHCP server has been configured by the
server administrator to use some other preference mechanism.
4.5. Sending a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message
The server unicasts the DHCPLEASEACTIVE or DHCPLEASEUNKNOWN message
to the address specified in giaddr field of DHCPLEASEQUERY message.
4.6. Receiving a DHCPLEASEACTIVE or DHCPLEASEUNKNOWN Message
When a DHCPLEASEACTIVE message is received in response to the
DHCPLEASEQUERY message, it means that there is currently an active
lease associated with the Remote ID in the DHCP server. The access
concentrator SHOULD use the information in the "htype", "hlen", and
"chaddr" fields of the DHCPLEASEACTIVE as well as Relay Agent
Information option information included in the packet to refresh its
location information for this IP address. An access concentrator is
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
time.
When a DHCPLEASEUNKNOWN message is received by an access concentrator
that had sent out a DHCPLEASEQUERY message, it means that the DHCP
server does not have definitive information concerning the DHCP
client specified in the Remote ID sub-option of the DHCPLEASEQUERY
message. The Access Concentrator MAY store this information for
future use. However, a DHCPLEASEQUERY SHOULD NOT be attempted with
the same Remote ID sub-option.
For leasequery by Remote ID, the impact of negative caching is
greatly reduced as the response leads to "definitive" information on
Kurapati, et al. Expires February 7, 2011 [Page 10]
Internet-Draft Query by Remote ID August 2010
all the hosts connected behind the connection. Note that in the case
of data-driven approach [RFC4388], a host spoofing several IP
addresses can lead to negative caching of greater magnitude. Another
important change this draft brings is the removal of "periodic"
leasequeries generated from negative caching caused by
DHCPLEASEUNKNOWN. Since the information obtained through query by
Remote ID is complete, there is no need of attempting leasequery
again for the same connection.
4.7. Receiving No Response to the DHCPLEASEQUERY Message
When an access concentrator receives no response to a DHCPLEASEQUERY
message, it should be handled in the same manner as suggested in RFC
4388 [RFC4388].
4.8. Lease Binding Data Storage Requirements
Implementation Note:
To generate replies for a lease query by Remote ID effeciently, a
DHCP server should index the lease binding data structures using
Remote ID.
4.9. Using the DHCPLEASEQUERY Message with Multiple DHCP Servers
This scenario should be handled in the same way it is done in RFC
4388 [RFC4388].
Kurapati, et al. Expires February 7, 2011 [Page 11]
Internet-Draft Query by Remote ID August 2010
5. RFC 4388 Considerations
This document is compatible with RFC 4388 [RFC4388] based
implementations, which means that a client that supports this
extension can work with a server not supporting this document,
provided it uses RFC 4388 [RFC4388] defined query types. Also, a
server supporting this document can work with a client not supporting
this query type. However, there are some changes that this document
proposes with respect to RFC 4388 [RFC4388]. Implementers extending
RFC 4388 [RFC4388] implementations to support this document, should
take note of the following points:
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,
the query will still be recognized as query by IP address/MAC
address/Client Identifier as specified by RFC 4388 [RFC4388].
o Section 6.4 of RFC 4388 [RFC4388] suggests that a DHCPLEASEUNKNOWN
MUST NOT have any other option present. But for a query by Remote
ID, option 82 MUST be present in the reply.
Kurapati, et al. Expires February 7, 2011 [Page 12]
Internet-Draft Query by Remote ID August 2010
6. Security Considerations
This document does not introduce any new security concerns beyond
those specified in the original leasequery protocol RFC 4388
[RFC4388] specifications.
Kurapati, et al. Expires February 7, 2011 [Page 13]
Internet-Draft Query by Remote ID August 2010
7. IANA Considerations
This document does not introduce any new namespaces for the IANA to
manage.
Kurapati, et al. Expires February 7, 2011 [Page 14]
Internet-Draft Query by Remote ID August 2010
8. Acknowledgments
Copious amounts of text in this document are derived from RFC 4388
[RFC4388]. Kim Kinnear, Damien Neil, Stephen Jacob and Alfred Hoenes
provided valuable feedback on this document
Kurapati, et al. Expires February 7, 2011 [Page 15]
Internet-Draft Query by Remote ID August 2010
9. References
9.1. Normative Reference
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4388] Woundy, R. and K. Kinnear, "Dynamic Host Configuration
Protocol (DHCP) Leasequery", RFC 4388, February 2006.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
[RFC3046] Patrick, M., "DHCP Relay Agent Information Option",
RFC 3046, January 2001.
9.2. Informative Reference
[RFC951] Croft, B. and J. Gilmore, "Bootstrap Protocol (BOOTP)",
RFC 951, September 1985.
[RFC1542] Wimer, W., "Clarifications and Extensions for the
Bootstrap Protocol", RFC 1542, October 1993.
[RFC2132] Droms, R. and S. Alexander, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
Kurapati, et al. Expires February 7, 2011 [Page 16]
Internet-Draft Query by Remote ID August 2010
Authors' Addresses
Pavan Kurapati
Juniper Networks Ltd.
Embassy Prime Buildings, C.V.Raman Nagar
Bangalore 560 093
India
Email: kurapati@juniper.net
URI: http://www.juniper.net/
D.T.V Ramakrishna Rao
Infosys Technologies Ltd.
44 Electronics City, Hosur Road
Bangalore 560 100
India
Email: ramakrishnadtv@infosys.com
URI: http://www.infosys.com/
Bharat Joshi
Infosys Technologies Ltd.
44 Electronics City, Hosur Road
Bangalore 560 100
India
Email: bharat_joshi@infosys.com
URI: http://www.infosys.com/
Kurapati, et al. Expires February 7, 2011 [Page 17]
