Network Working Group J. Brzozowski

Network Working Group J. Brzozowski
Request for Comments: 5007 Comcast Cable
Category: Standards Track K. Kinnear
B. Volz
S. Zeng
Cisco Systems, Inc.
September 2007

DHCPv6 Leasequery

Status of This Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

Abstract

This document specifies a leasequery exchange for the Dynamic Host
Configuration Protocol for IPv6 (DHCPv6) that can be used to obtain
lease information about DHCPv6 clients from a DHCPv6 server. This
document specifies the scope of data that can be retrieved as well as
both DHCPv6 leasequery requestor and server behavior. This document
extends DHCPv6.

Brzozowski, et al. Standards Track [Page 1]

RFC 5007 DHCPv6 Leasequery September 2007

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 4
3.1. On-Demand Query . . . . . . . . . . . . . . . . . . . . . 4
3.2. Anticipatory Query . . . . . . . . . . . . . . . . . . . . 5
3.3. Query Types . . . . . . . . . . . . . . . . . . . . . . . 5
4. Protocol Details . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Message and Option Definitions . . . . . . . . . . . . . . 6
4.1.1. Messages . . . . . . . . . . . . . . . . . . . . . . . 6
4.1.2. Options . . . . . . . . . . . . . . . . . . . . . . . 6
4.1.3. Status Codes . . . . . . . . . . . . . . . . . . . . . 12
4.1.4. Transmission and Retransmission Parameters . . . . . . 12
4.2. Message Validation . . . . . . . . . . . . . . . . . . . . 12
4.2.1. LEASEQUERY . . . . . . . . . . . . . . . . . . . . . . 12
4.2.2. LEASEQUERY-REPLY . . . . . . . . . . . . . . . . . . . 13
4.3. DHCPv6 Leasequery Requestor Behavior . . . . . . . . . . . 13
4.3.1. Creation of LEASEQUERY . . . . . . . . . . . . . . . . 13
4.3.2. Transmission of LEASEQUERY . . . . . . . . . . . . . . 13
4.3.3. Receipt of LEASEQUERY-REPLY . . . . . . . . . . . . . 14
4.3.4. Handling DHCPv6 Client Data from Multiple Sources . . 15
4.4. DHCPv6 Leasequery Server Behavior . . . . . . . . . . . . 16
4.4.1. Receipt of LEASEQUERY Messages . . . . . . . . . . . . 16
4.4.2. Constructing the Client's OPTION_CLIENT_DATA . . . . . 17
4.4.3. Transmission of LEASEQUERY-REPLY Messages . . . . . . 17
5. Security Considerations . . . . . . . . . . . . . . . . . . . 17
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
8.1. Normative References . . . . . . . . . . . . . . . . . . . 20
8.2. Informative References . . . . . . . . . . . . . . . . . . 20

Brzozowski, et al. Standards Track [Page 2]

RFC 5007 DHCPv6 Leasequery September 2007

1. Introduction

The DHCPv6 [2] protocol specifies a mechanism for the assignment of
both IPv6 address and configuration information to IPv6 nodes. IPv6
Prefix Options for DHCPv6 [4] specifies a mechanism for the automated
delegation of IPv6 prefixes and related options. Similar to DHCPv4
[5], DHCPv6 servers maintain authoritative information related to
their operations including, but not limited to, lease information for
IPv6 addresses and delegated prefixes.

The requirement exists in various types of IPv6 deployments,
particularly those of a broadband variety, to leverage DHCPv6 [2] for
retrieving data related to the operation of DHCPv6 servers
programmatically. In particular, it is desirable to be able to
extract lease information about IPv6 addresses and delegated prefixes
assigned using DHCPv6 [2] [4]. Specific examples where this
information has illustrated value are in broadband networks to
facilitate access control by edge devices. This capability to
programmatically extract lease data from the DHCPv6 server is called
leasequery.

The leasequery capability described in this document parallels the
DHCPv4 leasequery capability documented in [3]. As such, it shares
the basic motivations, background, design goals and constraints as
described in [3]. Differences are due to the differences between
IPv4 and IPv6 and by extension, DHCPv4 and DHCPv6. For example,
Neighbor Discovery [7] is used in IPv6 instead of the Address
Resolution Protocol (ARP) [8] (Section 4.1 of [3]) and DOCSIS 3.0
[11] defines IPv6 support for cable modem environments.

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 [1].

DHCPv6 terminology is defined in [2]. Terminology specific to DHCPv6
leasequery can be found below:

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 DHCPv6 relay
agent functionality.

Brzozowski, et al. Standards Track [Page 3]

RFC 5007 DHCPv6 Leasequery September 2007

client(s) The nodes that have one or more bindings with a
DHCPv6 server. This does not refer to the node
issuing the LEASEQUERY unless it itself has one or
more bindings with a DHCPv6 server.

gleaning Gleaning is the extraction of location information
from DHCPv6 messages, as the messages are forwarded
by the DHCP relay agent function.

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 circuit that leads to the host, and/or the
hardware address of the intervening subscriber modem.

requestor The node that sends LEASEQUERY messages to one or
more servers to retrieve information on the bindings
for a client.

3. Protocol Overview

The focus of this document is to extend the DHCPv6 protocol to allow
processes and devices that wish to access information from a DHCPv6
server to do so in a lightweight and convenient manner. It is
especially appropriate for processes and devices that already
interpret DHCPv6 messages.

The LEASEQUERY message is a query message only and does not affect
the state of the IPv6 address or prefix, or the binding information
associated with it.

One important motivating example is that the LEASEQUERY message
allows access concentrators to query DHCP servers to obtain location
information of broadband access network devices. This is described
in Section 1 of [3] for IPv4.

3.1. On-Demand Query

The on-demand leasequery capability allows requesting just the
information necessary to satisfy an immediate need. If the requestor
is an access concentrator, then the immediate need will typically be
that it has received an IPv6 packet and it needs to refresh its
information concerning the DHCPv6 client to which that IPv6 address
is currently leased. In this case, the request will be by address.
This fits clearly into the single request/response cycle common to
other DHCPv6 message exchanges.

Brzozowski, et al. Standards Track [Page 4]

RFC 5007 DHCPv6 Leasequery September 2007

However, this approach has limitations when used with prefix
delegation [4] as no traffic may arrive because the access
concentrator is unable to inject the appropriate routing information
into the routing infrastructure, such as after a reboot. This
approach does work if the access concentrator is configured to inject
routing information for a prefix that aggregates potentially
delegated prefixes. Or, it also works if the access concentrator and
requesting router use a routing protocol; as then the requesting
router can trigger the access concentrator to request information
from a DHCPv6 server and inject appropriate routing information into
the routing infrastructure.

3.2. Anticipatory Query

A second approach for requesting information from a DHCPv6 server
would be to use a leasequery-like capability to rebuild an internal
data store containing information available from a DHCPv6 server.
The rebuilding of the data store in this approach can take place as
soon as possible after the need to rebuild it is discovered (such as
on booting), and doesn't wait on the receipt of specific packets to
trigger a piecemeal database update (as is the case for on-demand
leasequery). This approach would also remove the limitation
discussed above for prefix delegation.

This anticipatory query is not specified in this document and is an
area of future work.

3.3. Query Types

Leasequery provides for the following queries:

Query by IPv6 address - This query allows a requestor to request
from a server the bindings for a client that either is bound to
the address or has been delegated the prefix that contains the
address.

Query by Client Identifier (DUID) - This query allows a requestor to
request from a server the bindings for a specific client on a
specific link or a list of the links on which the client has one
or more bindings.

Brzozowski, et al. Standards Track [Page 5]

RFC 5007 DHCPv6 Leasequery September 2007

4. Protocol Details

4.1. Message and Option Definitions

4.1.1. Messages

The LEASEQUERY and LEASEQUERY-REPLY messages use the Client/Server
message formats described in [2], Section 6. Two new message codes
are defined:

LEASEQUERY (14) - A requestor sends a LEASEQUERY message to any
available server to obtain information on a client's leases. The
options in an OPTION_LQ_QUERY determine the query.

LEASEQUERY-REPLY (15) - A server sends a LEASEQUERY-REPLY message
containing client data in response to a LEASEQUERY message.

4.1.2. Options

4.1.2.1. Query Option

The Query option is used only in a LEASEQUERY message and identifies
the query being performed. The option includes the query type, link-
address (or 0::0), and option(s) to provide data needed for the
query.

The format of the Query option is shown below:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_LQ_QUERY | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| query-type | |
+-+-+-+-+-+-+-+-+ |
| |
| link-address |
| |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | .
+-+-+-+-+-+-+-+-+ .
. query-options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_LQ_QUERY (44)

option-len 17 + length of query-options field.

Brzozowski, et al. Standards Track [Page 6]

RFC 5007 DHCPv6 Leasequery September 2007

link-address A global address that will be used by the
server to identify the link to which the
query applies, or 0::0 if unspecified.

query-type The query requested (see below).

query-options The options related to the query.

The query-type and required query-options are:

QUERY_BY_ADDRESS (1) - The query-options MUST contain an
OPTION_IAADDR option [2]. The link-address field, if not 0::0,
specifies an address for the link on which the client is located
if the address in the OPTION_IAADDR option is of insufficient
scope. Only the information for the client that has a lease for
the specified address or was delegated a prefix that contains the
specified address is returned (if available).

QUERY_BY_CLIENTID (2) - The query-options MUST contain an
OPTION_CLIENTID option [2]. The link-address field, if not 0::0,
specifies an address for the link on which the client is located.
If the link-address field is 0::0, the server SHOULD search all of
its links for the client.

The query-options MAY also include an OPTION_ORO option [2] to
indicate the options for each client that the requestor would like
the server to return. Note that this OPTION_ORO is distinct and
separate from an OPTION_ORO that may be in the requestor's LEASEQUERY
message.

If a server receives an OPTION_LQ_QUERY with a query-type it does not
support, the server SHOULD return an UnknownQueryType status-code.
If a server receives a supported query-type but the query-options is
missing a required option, the server SHOULD return a MalformedQuery
status-code.

Brzozowski, et al. Standards Track [Page 7]

RFC 5007 DHCPv6 Leasequery September 2007

4.1.2.2. Client Data Option

The Client Data option is used to encapsulate the data for a single
client on a single link in a LEASEQUERY-REPLY message.

The format of the Client Data option is shown below:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_CLIENT_DATA | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. client-options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_CLIENT_DATA (45)

option-len Length, in octets, of the encapsulated client-
options field.

client-options The options associated with this client.

The encapsulated client-options include the OPTION_CLIENTID,
OPTION_IAADDR, OPTION_IAPREFIX, and OPTION_CLT_TIME options and other
options specific to the client and requested by the requestor in the
OPTION_ORO in the OPTION_LQ_QUERY's query-options. The server MUST
return all of the client's statefully assigned addresses and
delegated prefixes, with a non-zero valid lifetime, on the link.

Brzozowski, et al. Standards Track [Page 8]

RFC 5007 DHCPv6 Leasequery September 2007

4.1.2.3. Client Last Transaction Time Option

The Client Last Transaction Time option is encapsulated in an
OPTION_CLIENT_DATA and identifies how long ago the server last
communicated with the client, in seconds.

The format of the Client Last Transaction Time option is shown below:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_CLT_TIME | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| client-last-transaction-time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_CLT_TIME (46)

option-len 4

client-last-transaction-time
The number of seconds since the server last
communicated with the client (on that link).

The client-last-transaction-time is a positive value and reflects the
number of seconds since the server last communicated with the client
(on that link).

Brzozowski, et al. Standards Track [Page 9]

RFC 5007 DHCPv6 Leasequery September 2007

4.1.2.4. Relay Data

The Relay Data option is used only in a LEASEQUERY-REPLY message and
provides the relay agent information used when the client last
communicated with the server.

The format of the Relay Data option is shown below:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_LQ_RELAY_DATA | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| peer-address (IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| DHCP-relay-message |
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_LQ_RELAY_DATA (47)

option-len 16 + length of DHCP-relay-message.

peer-address The address of the relay agent from which
the relayed message was received by the
server.

DHCP-relay-message
The last complete relayed message, excluding
the client's message OPTION_RELAY_MSG,
received by the server.

This option is used by the server to return full relay agent
information for a client. It MUST NOT be returned if the server does
not have such information, either because the client communicated
directly (without relay agent) with the server or if the server did
not retain such information.

If returned, the DHCP-relay-message MUST contain a valid (perhaps
multi-hop) RELAY-FORW message as the most recently received by the
server for the client. However, the (innermost) OPTION_RELAY_MSG
option containing the client's message MUST have been removed.

Brzozowski, et al. Standards Track [Page 10]

RFC 5007 DHCPv6 Leasequery September 2007

This option SHOULD only be returned if requested by the OPTION_ORO of
the OPTION_LQ_QUERY.

4.1.2.5. Client Link Option

The Client Link option is used only in a LEASEQUERY-REPLY message and
identifies the links on which the client has one or more bindings.
It is used in reply to a query when no link-address was specified and
the client is found to be on more than one link.

The format of the Client Link option is shown below:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_LQ_CLIENT_LINK | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| link-address (IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| link-address (IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code OPTION_LQ_CLIENT_LINK (48)

option-len Length of the list of links in octets;
must be a multiple of 16.

link-address A global address used by the server to
identify the link on which the client is
located.

A server may respond to a query by client-id, where the 0::0 link-
address was specified, with this option if the client is found to be
on multiple links. The requestor may then repeat the query once for
each link-address returned in the list, specifying the returned link-
address. If the client is on a single link, the server SHOULD return
the client's data in an OPTION_CLIENT_DATA option.

Brzozowski, et al. Standards Track [Page 11]

RFC 5007 DHCPv6 Leasequery September 2007

4.1.3. Status Codes

The following new status codes are defined:

UnknownQueryType (7) - The query-type is unknown to or not supported
by the server.

MalformedQuery (8) - The query is not valid; for example, a required
query-option is missing from the OPTION_LQ_QUERY.

NotConfigured (9) - The server does not have the target address or
link in its configuration.

NotAllowed (10) - The server does not allow the requestor to issue
this LEASEQUERY.

4.1.4. Transmission and Retransmission Parameters

This section presents a table of values used to describe the message
transmission behavior for leasequery.

Parameter Default Description
----------------------------------
LQ_TIMEOUT 1 sec Initial LEASEQUERY timeout
LQ_MAX_RT 10 secs Max LEASEQUERY timeout value
LQ_MAX_RC 5 Max LEASEQUERY retry attempts

4.2. Message Validation

4.2.1. LEASEQUERY

Requestors and clients MUST discard any received LEASEQUERY messages.

Servers MUST discard any received LEASEQUERY messages that meet any
of the following conditions:

o the message does not include an OPTION_CLIENTID option.

o the message includes an OPTION_SERVERID option but the contents of
the OPTION_SERVERID option does not match the server's identifier.

o the message does not include an OPTION_LQ_QUERY option.

Brzozowski, et al. Standards Track [Page 12]

RFC 5007 DHCPv6 Leasequery September 2007

4.2.2. LEASEQUERY-REPLY

Requestors MUST discard any received LEASEQUERY-REPLY messages that
meet any of the following conditions:

o the message does not include an OPTION_SERVERID option.

o the message does not include an OPTION_CLIENTID option, or the
contents of the OPTION_CLIENTID option do not match the DUID of
the requestor.

o the "transaction-id" field in the message does not match the value
used in the original message.

Servers and Relay Agents (on the server port, 547 [2]) MUST discard
any received LEASEQUERY-REPLY messages.

4.3. DHCPv6 Leasequery Requestor Behavior

This section describes how a requestor initiates lease data retrieval
from DHCPv6 servers.

4.3.1. Creation of LEASEQUERY

The requestor sets the "msg-type" field to LEASEQUERY. The requestor
generates a transaction ID and inserts this value in the
"transaction-id" field.

The requestor MUST include an OPTION_CLIENTID option to identify
itself to the server.

The requestor MUST include an OPTION_LQ_QUERY option and set the
query-type, link-address, and query-options as appropriate to the
query-type (Section 4.1.2.1).

The requestor SHOULD include an OPTION_SERVERID if it is not
unicasting the LEASEQUERY yet only wants a response from a specific
server.

4.3.2. Transmission of LEASEQUERY

The requestor MAY be configured to use a list of destination
addresses, which MAY include unicast addresses, the All_DHCP_Servers
multicast address, or other addresses selected by the network
administrator. If the requestor has not been explicitly configured,
it MAY use the All_DHCP_Servers multicast address as the default.

Brzozowski, et al. Standards Track [Page 13]

RFC 5007 DHCPv6 Leasequery September 2007

The requestor SHOULD send LEASEQUERY to one or more DHCPv6 servers
that are known to possess authoritative information concerning the
query target.

In the absence of information concerning which DHCPv6 servers might
possess authoritative information on the query target, the requestor
SHOULD send LEASEQUERY to all DHCPv6 servers that the requestor knows
about or is configured with. For example, the requestor MAY send
LEASEQUERY to the All_DHCP_Servers multicast address.

The requestor transmits LEASEQUERY messages according to Section 14
of [2], using the following parameters:

IRT LQ_TIMEOUT
MRT LQ_MAX_RT
MRC LQ_MAX_RC
MRD 0

If the message exchange fails, the requestor takes an action based on
the requestor's local policy. Examples of actions the requestor
might take include:

o Select another server from a list of servers known to the
requestor.

o Send to multiple servers by multicasting to the All_DHCP_Servers
address.

o Terminate the request.

4.3.3. Receipt of LEASEQUERY-REPLY

A successful LEASEQUERY-REPLY is one without an OPTION_STATUS_CODE
option (or an OPTION_STATUS_CODE option with a success code). There
are three variants:

1. If the server had bindings for the requested client, the message
includes an OPTION_CLIENT_DATA option and the requestor extracts
the client data from the LEASEQUERY-REPLY and updates its binding
information database. If the OPTION_CLIENT_DATA contains no
OPTION_CLT_TIME, the requestor SHOULD silently discard the
OPTION_CLIENT_DATA option.

2. If the server found bindings for the client on multiple links,
the message includes an OPTION_CLIENT_LINK option. The requestor
will need to reissue LEASEQUERY messages using each of the
returned link-addresses to obtain the client's bindings.

Brzozowski, et al. Standards Track [Page 14]

RFC 5007 DHCPv6 Leasequery September 2007

3. If the server had no bindings for the client, neither the
OPTION_CLIENT_DATA nor OPTION_CLIENT_LINK option will be present.

An unsuccessful LEASEQUERY-REPLY is one that has an
OPTION_STATUS_CODE with an error code. Depending on the status code,
the requestor may try a different server (such as for NotAllowed,
NotConfigured, and UnknownQueryType), try a different or corrected
query (such as for UnknownQueryType and MalformedQuery), or terminate
the query.

4.3.4. Handling DHCPv6 Client Data from Multiple Sources

A requestor may receive lease data on the same client from the same
DHCPv6 server in response to different types of LEASEQUERY. If a
LEASEQUERY is sent to multiple servers, the requestor may receive
from several servers lease data on the same DHCPv6 client. This
section describes how the requestor handles multiple lease data
sources on the same DHCPv6 client from the same server or different
servers.

The client data from the different sources may be disjoint or
overlapping. The disjoint and overlapping relationship can happen
between data from the same server or different servers.

If client data from two sources on the same client are of different
types or values, then the data are disjoint. An example of data of
different types is when a requestor receives an IPv6 address lease
from one server and a prefix lease from another server, both assigned
to the same client. An example of different values (but the same
type) is when a requestor receives two IPv6 address leases from two
different servers, both assigned to the same client, but the leases
are on two different IPv6 addresses. If the requestor receives
disjoint client data from different sources, it SHOULD merge them.

If client data from two sources on the same client are of the same
type and value, then the data are overlapping. An example of
overlapping data is when a requestor receives a lease on the same
IPv6 address from two different servers. Overlapping client data are
also called conflicting data.

The requestor SHOULD use the OPTION_CLT_TIME to resolve data
conflicts originated from different servers, and SHOULD accept data
with most recent OPTION_CLT_TIME.

Brzozowski, et al. Standards Track [Page 15]

RFC 5007 DHCPv6 Leasequery September 2007

4.4. DHCPv6 Leasequery Server Behavior

A DHCPv6 server sends LEASEQUERY-REPLY messages in response to valid
LEASEQUERY messages it receives to return the statefully assigned
addresses, delegated prefixes, and other information that match the
query.

4.4.1. Receipt of LEASEQUERY Messages

Upon receipt of a valid LEASEQUERY message, the DHCPv6 server locates
the requested client, collects data on the client, and constructs and
returns a LEASEQUERY-REPLY. A LEASEQUERY message cannot be used to
assign, release, or otherwise modify bindings or other configuration
information.

The server constructs a LEASEQUERY-REPLY message by setting the "msg-
type" field to LEASEQUERY-REPLY, and copying the transaction ID from
the LEASEQUERY message into the transaction-id field.

If the query-type in the OPTION_LQ_QUERY option is not a known or
supported value, the server adds an OPTION_STATUS_CODE option with
the UnknownQueryType status code and sends the LEASEQUERY-REPLY to
the requestor. If the query-options do not contain the required
options for the query-type, the server adds an OPTION_STATUS_CODE
option with the MalformedQuery status code and sends the LEASEQUERY-
REPLY to the client.

A server may also restrict LEASEQUERY messages, or query-types, to
certain requestors. In this case, the server MAY discard the
LEASEQUERY message or MAY add an OPTION_STATUS_CODE option with the
NotAllowed status code and send the LEASEQUERY-REPLY to the
requestor.

If the OPTION_LQ_QUERY specified a non-zero link-address, the server
MUST use the link-address to find the appropriate link for the
client. For a QUERY_BY_ADDRESS, if the 0::0 link-address was
specified, the server uses the address from the OPTION_IAADDR option
to find the appropriate link for the client. In either of these
cases, if the server is unable to find the link, it SHOULD return an
OPTION_STATUS_CODE option with the NotConfigured status and send the
LEASEQUERY-REPLY to the requestor.

For a QUERY_BY_CLIENTID, if a 0::0 link-address was specified, the
server MUST search all of its links for the client. If the client is
only found on a single link, the server SHOULD return that client's
data in an OPTION_CLIENT_DATA option. If the client is found on more

Brzozowski, et al. Standards Track [Page 16]

RFC 5007 DHCPv6 Leasequery September 2007

than a single link, the server MUST return the list of links in the
OPTION_CLIENT_LINK option; the server MUST NOT return any client
data.

Otherwise, the server uses the data in the OPTION_LQ_QUERY to
initiate the query. The result of the query will be zero or one
client. This will result in zero or one OPTION_CLIENT_DATA option
being added to the LEASEQUERY-REPLY.

4.4.2. Constructing the Client's OPTION_CLIENT_DATA

An OPTION_CLIENT_DATA option in a LEASEQUERY-REPLY message MUST
minimally contain the following options:
1. OPTION_CLIENTID
2. OPTION_IAADDR and/or OPTION_IAPREFIX
3. OPTION_CLT_TIME

Depending on the bindings the client has on a link, either
OPTION_IAADDR options, OPTION_IAPREFIX options, or both may be
present.

The OPTION_CLIENT_DATA SHOULD include options requested in the
OPTION_ORO of the OPTION_LQ_QUERY option in the LEASEQUERY message
and that are acceptable to return based on the list of "sensitive
options", discussed below.

DHCPv6 servers SHOULD be configurable with a list of "sensitive
options" that must not be returned to the requestor when specified in
the OPTION_ORO of the OPTION_LQ_QUERY option in the LEASEQUERY
message. Any option on this list MUST NOT be returned to a
requestor, even if requested by that requestor.

4.4.3. Transmission of LEASEQUERY-REPLY Messages

The server sends the LEASEQUERY-REPLY message as described in the
"Transmission of Reply Messages" section of [2].

5. Security Considerations

Access concentrators are expected to be common leasequery requestors.
Access concentrators that use DHCPv6 gleaning (i.e., [10]), refreshed
with LEASEQUERY messages, will maintain accurate client/binding
information. This ensures that the access concentrator can forward
data traffic to the intended destination in the broadband access
network, can perform IPv6 source address verification of datagrams
from the access network, and can encrypt traffic that can only be

Brzozowski, et al. Standards Track [Page 17]

RFC 5007 DHCPv6 Leasequery September 2007

decrypted by the intended access modem (e.g., [12] and [13]). Thus,
the leasequery capability allows an access concentrator to provide
considerably enhanced security.

The "Security Considerations" section of [2] details the general
threats to DHCPv6, and thus to LEASEQUERY messages. The
"Authentication of DHCP Messages" section of [2] describes securing
communication between relay agents and servers, as well as clients
and servers. If the requestor is an access concentrator, the IPsec-
based [9] security as described in [2] Section 21.1 SHOULD be used.
Other types of requestors are essentially DHCPv6 clients. Thus,
DHCPv6 authentication, Section 21 of [2], is an appropriate mechanism
for securing LEASEQUERY and LEASEQUERY-REPLY messages. As the number
of leasequery requestors and servers in an administrative domain is
relatively small, any shared key distribution issues are minimized.

After implementing the above approaches, the DHCPv6 server should
only be communicating with trusted LEASEQUERY requestors, and so
security needs should be met.

However, not all traffic originates directly from these trusted
requestors. For example, trusted relay agents can relay LEASEQUERY
messages from untrusted requestors or elsewhere in the network. This
SHOULD be prevented at least at the perimeter relay agents (or on all
relay agents unless relayed LEASEQUERY messages are required for some
requestors). DHCPv6 servers MAY be configured to discard relayed
LEASEQUERY messages or restrict relay chaining.

DHCPv6 servers SHOULD also provide for the ability to restrict the
information returned for a client in a LEASEQUERY-REPLY even to a
trusted LEASEQUERY requestor, as described in Section 4.4.2.

Since even trusted access concentrators may generate LEASEQUERY
requests as a result of activity external to the access concentrator,
access concentrators SHOULD minimize potential denial-of-service
attacks on the DHCPv6 servers by minimizing the generation of
LEASEQUERY messages. In particular, the access concentrator SHOULD
employ negative caching (i.e., cache the fact that a particular
recent query failed to return client data) and address restrictions
where possible (i.e., don't send a LEASEQUERY message for addresses
outside the range of the attached broadband access networks).
Together, these mechanisms limit the access concentrator to
transmitting one LEASEQUERY message (excluding message retries) per
legitimate broadband access network address after a reboot event.

Packet-flooding denial-of-service attacks can result in the
exhaustion of processing resources, thus preventing the server from
serving legitimate and regular DHCPv6 clients as well as legitimate

Brzozowski, et al. Standards Track [Page 18]

RFC 5007 DHCPv6 Leasequery September 2007

DHCPv6 LEASEQUERY requestors, denying configurations to legitimate
DHCPv6 clients as well lease information to legitimate DHCPv6
LEASEQUERY requestors. While these attacks are unlikely when only
communicating with trusted LEASEQUERY requestors, the possibility
always exists that the trust is misplaced, security techniques are
compromised, or even trusted requestors can have bugs in them.
Therefore, techniques for defending against packet-flooding denial of
service are always a good idea, and they include good perimeter
security, as mentioned earlier, and rate limiting DHCPv6 traffic by
relay agents, other network elements, or the server itself.

One way to attack an access concentrator (as opposed to a DHCPv6
server) as a LEASEQUERY requestor is the establishment of a malicious
server with the intent of providing incorrect lease or route
information to the access concentrator, thwarting source IPv6 address
verification, and preventing correct routing. This type of attack
can be minimized by using IPsec as described in Section 21.1 of [2].

6. IANA Considerations

IANA has assigned the following new DHCPv6 Message types in the
registry maintained in
http://www.iana.org/assignments/dhcpv6-parameters:

LEASEQUERY
LEASEQUERY-REPLY

IANA has assigned the following new DHCPv6 Option Codes in the
registry maintained in
http://www.iana.org/assignments/dhcpv6-parameters:

OPTION_LQ_QUERY
OPTION_CLIENT_DATA
OPTION_CLT_TIME
OPTION_LQ_RELAY_DATA
OPTION_LQ_CLIENT_LINK

IANA has assigned the following new DHCPv6 Status Codes in the
registry maintained in
http://www.iana.org/assignments/dhcpv6-parameters:

UnknownQueryType
MalformedQuery
NotConfigured
NotAllowed

Brzozowski, et al. Standards Track [Page 19]

RFC 5007 DHCPv6 Leasequery September 2007

IANA has created a new registry for the OPTION_LQ_QUERY option query-
type codes in the registry maintained in
http://www.iana.org/assignments/dhcpv6-parameters with the following
initial assignments:

QUERY_BY_ADDRESS 1
QUERY_BY_CLIENTID 2

New OPTION_LQ_QUERY option query-type codes are assigned through
Standards Action, as defined in [6].

7. Acknowledgements

Thanks to Ralph Droms, Richard Johnson, Josh Littlefield, Hemant
Singh, Pak Siripunkaw, Markus Stenberg, and Ole Troan for their
input, ideas, and review during the production of this document.

8. References

8.1. Normative References

[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.

[2] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M.
Carney, "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", RFC 3315, July 2003.

[3] Woundy, R. and K. Kinnear, "Dynamic Host Configuration Protocol
(DHCP) Leasequery", RFC 4388, February 2006.

[4] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host
Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.

8.2. Informative References

[5] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997.

[6] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.

[7] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998.

Brzozowski, et al. Standards Track [Page 20]

RFC 5007 DHCPv6 Leasequery September 2007

[8] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet
address for transmission on Ethernet hardware", STD 37,
RFC 826, November 1982.

[9] Kent, S. and K. Seo, "Security Architecture for the Internet
Protocol", RFC 4301, December 2005.

[10] Droms, R., "DHCPv6 Relay Agent Assignment Notification (RAAN)
Option", Work in Progress, November 2006.

[11] CableLabs, "Data-Over-Cable Service Interface Specifications:
DOCSIS 3.0, MAC and Upper Layer Protocols Interface
Specification, CM-SP-MULPIv3.0-I04-070518", May 2007, available
at http://www.cablemodem.com/.

[12] SCTE Data Standards Subcommittee, "Data-Over-Cable Service
Interface Specifications: DOCSIS 1.0 Baseline Privacy Interface
Specification SCTE 22-2 2002", 2002, available at
http://www.scte.org/standards/.

[13] CableLabs, "Data-Over-Cable Service Interface Specifications:
Baseline Privacy Plus Interface Specification CM-SP-BPI+_I12-
050812", August 2005, available at http://www.cablemodem.com/.

Brzozowski, et al. Standards Track [Page 21]

RFC 5007 DHCPv6 Leasequery September 2007

Authors' Addresses

John Jason Brzozowski
Comcast Cable
1800 Bishops Gate Boulevard
Mt. Laurel, NJ 08054
USA

Phone: +1 856 324 2671
EMail: [email protected]

Kim Kinnear
Cisco Systems, Inc.
1414 Massachusetts Ave.
Boxborough, MA 01719
USA

Phone: +1 978 936 0000
EMail: [email protected]

Bernard Volz
Cisco Systems, Inc.
1414 Massachusetts Ave.
Boxborough, MA 01719
USA

Phone: +1 978 936 0000
EMail: [email protected]

Shengyou Zeng
Cisco Systems, Inc.
1414 Massachusetts Ave.
Boxborough, MA 01719
USA

Phone: +1 978 936 0000
EMail: [email protected]

Brzozowski, et al. Standards Track [Page 22]

RFC 5007 DHCPv6 Leasequery September 2007

Full Copyright Statement

Copyright (C) The IETF Trust (2007).

This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.

This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.

Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.

The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
[email protected].

Brzozowski, et al. Standards Track [Page 23]