DHC Working Group Kim Kinnear
Internet Draft Bernie Volz
Intended Status: Standards Track Neil Russell
Expires: May 3, 2009 Mark Stapp
Cisco Systems, Inc.
D. Rao
B. Joshi
P. Kurapati
Infosys Technologies Ltd.
November 3, 2008
Bulk DHCPv4 Lease Query
<draft-kinnear-dhc-dhcpv4-bulk-leasequery-01.txt>
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
The Dynamic Host Configuration Protocol for IPv4 (DHCPv4) has been
extended with a Leasequery capability that allows a requestor to
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request information about DHCPv4 bindings. That mechanism is limited
to queries for individual bindings. In some situations individual
binding queries may not be efficient, or even possible. This
document expands on the DHCPv4 Leasequery protocol to allow for bulk
transfer of DHCPv4 address binding data via TCP.
Table of Contents
1. Introduction................................................. 3
2. Terminology.................................................. 4
3. Motivation................................................... 6
4. Design Goals................................................. 8
4.1. Information Acquisition before Data Starts................. 8
4.2. Lessen Negative Caching.................................... 8
4.3. Antispoofing in 'Fast Path'................................ 8
4.4. Minimize data transmission................................. 8
5. Protocol Overview............................................ 9
6. Interaction Between UDP Leasequery and Bulk Leasequery....... 10
7. Message and Option Definitions............................... 11
7.1. Message Framing for TCP.................................... 11
7.2. New or Changed Options..................................... 12
7.3. Connection and Transmission Parameters..................... 20
8. Requestor Behavior........................................... 20
8.1. Connecting and General Processing.......................... 20
8.2. Forming a Bulk Leasequery.................................. 21
8.3. Processing Bulk Replies.................................... 23
8.4. Processing Time Values in Leasequery messages.............. 25
8.5. Querying Multiple Servers.................................. 27
8.6. Making Sense Out of Multiple Responses Concerning a Single. 27
8.7. Multiple Queries to a Single Server over One Connection.... 28
8.8. Closing Connections........................................ 29
9. Server Behavior.............................................. 30
9.1. Accepting Connections...................................... 30
9.2. Replying to a Bulk Leasequery.............................. 30
9.3. Building a Single Reply for Bulk Leasequery................ 34
9.4. Multiple or Parallel Queries............................... 35
9.5. Closing Connections........................................ 36
10. Security Considerations..................................... 36
11. IANA Considerations......................................... 37
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12. Acknowledgements............................................ 38
13. References.................................................. 38
13.1. Normative References...................................... 38
13.2. Informative References.................................... 39
14. Authors' Addresses.......................................... 39
15. Full Copyright Statement.................................... 41
16. Intellectual Property....................................... 41
17. Acknowledgment.............................................. 41
18. Appendix -- Why a New Leasequery is Required................ 42
1. Introduction
The DHCPv4 protocol [RFC2131] [RFC2132] specifies a mechanism for the
assignment of IPv4 address and configuration information to IPv4
nodes. DHCPv4 servers maintain authoritative binding information.
+--------+
| DHCPv4 | +--------------+
| Server |-...-| DSLAM |
| | | Relay Agent |
+--------+ +--------------+
| |
+------+ +------+
|Modem1| |Modem2|
+------+ +------+
| | |
+-----+ +-----+ +-----+
|Host1| |Host2| |Host3|
+-----+ +-----+ +-----+
Figure 1: Example DHCPv4 configuration
DHCPv4 relay agents receive DHCPv4 messages and frequently append a
relay agent information option [RFC3046] before relaying them to the
configured DHCPv4 servers (see Figure 1). In this process, some
relay agents also glean the lease information sent by the server and
maintain this locally. This information is used for a variety of
purposes, including prevention of spoofing attempts from the DHCPv4
clients and to install routes. When a relay agent reboots, this
information is frequently lost.
The DHCPv4 Leasequery capability [RFC4388] extends the basic DHCPv4
capability to allow an external entity, such as a relay agent, to
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query a DHCPv4 server to recover lease state information about a
particular IP address or client in near real-time.
The existing query types in Leasequery are typically data driven; the
relay agent initiates the Leasequery when it receives data traffic
from or to the client. This approach may not scale well when there
are thousands of clients connected to the relay agent or when the
relay agent has a need to rebuild its internal data store prior to
processing traffic in one direction or another.
Different query types are needed where a relay agent can query the
server without waiting for the traffic from or for the clients, as
well as a different transmission technique more conducive to the
transmission of large quantities of data.
This document extends the DHCPv4 Leasequery protocol to add support
for queries that address these additional requirements. There may be
many thousands of DHCPv4 bindings returned as the result of a single
request, so TCP [RFC4614] is specified for efficiency of data
transfer. We define several additional query types, each of which
could return multiple responses, in order to meet a variety of
requirements.
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 "absolute time"
A 32-bit quantity containing the number of seconds since Jan 1,
1970.
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
DHCPv4 relay agent functionality.
o "active binding"
An IP address with an active binding refers to an IP address
which is currently associated with a DHCPv4 client where that
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DHCPv4 client has the right to use the IP address.
o "Bulk Leasequery"
Requesting and receiving the existing DHCPv4 address binding
information in an efficient manner.
o "clock skew"
The difference between the absolute time on a DHCPv4 server and
the absolute time on the system where a requestor of a Bulk
Leasequery is executing is termed the "clock skew" for that Bulk
Leasequery connection. It is not absolutely constant but is
likely to vary only slowly. It is possible that, when both
systems run NTP, that the clock skew is zero, and this is not
only acceptable, but desired.
While it is easy to think that this can be calculated precisely
after one message is received by a requestor from a DHCPv4
server, a more accurate value is derived from continuously
examining the instantaneous value developed from each message
received from a DHCPv4 server and using it to make small
adjustments to the existing value held in the requestor.
o "DHCPv4 client"
A DHCPv4 client is an Internet host using DHCPv4 to obtain
configuration parameters such as a network address.
o "DHCPv4 relay agent"
A DHCPv4 relay agent is a third-party agent that transfers BOOTP
and DHCPv4 messages between clients and servers residing on
different subnets, per [RFC951] and [RFC1542].
o "DHCPv4 server"
A DHCPv4 server is an Internet host that returns configuration
parameters to DHCPv4 clients.
o "downstream"
Refers to a direction away from the central part of a network
and toward the edge. In a DHCPv4 context, typically refers to a
network direction which is away from the DHCPv4 server.
o "IP address"
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In this document, the term "IP address" refers to an IPv4 IP
address.
o "IP address binding"
The information that a DHCPv4 server keeps regarding the
relationship between a DHCPv4 client and an IPv4 IP address.
This includes the identity of the DHCPv4 client and the
expiration time, if any, of any lease that client has on a
particular IPv4 address. In some contexts, this may include
information on IP addresses that are currently associated with
DHCPv4 clients, and in others it may also include IP addresses
with no current association to a DHCPv4 client.
o "MAC address"
In the context of a DHCPv4 message, a MAC address consists of
the fields: hardware type "htype", hardware length "hlen", and
client hardware address "chaddr".
o "upstream"
Refers to a direction toward the central part of a network and
away from the edge. In a DHCPv4 context, typically refers to a
network direction which is toward the DHCPv4 server.
o "stable storage"
Stable storage is used to hold information concerning IP address
bindings (among other things) so that this information is not
lost in the event of a failure which requires restart of the
network element. DHCPv4 servers are typically expected to have
high speed access to stable storage, while relay agents and
access concentrators usually do not have access to stable
storage, although they may have periodic access to such storage.
o "xid"
Transaction-id. The term "xid" refers to the DHCPv4 field
containing the transaction-id of the message.
3. Motivation
Consider a typical DSLAM working also as a DHCPv4 relay agent (see
Figure 1). Typically, both a "fast path" and a "slow path" exist in
many network elements, including DSLAMs. Fast path processing is
done in a network processor or in an ASIC (Application Specific
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Integrated Circuit). Slow path processing is done in a normal
processor. As much as possible, regular data handling code should be
in the fast path. Slow path processing should be reduced as it may
become a bottleneck.
For a DSLAM having multiple DSL ports, multiple IP addresses may be
assigned using DHCPv4 to a single port and the number of DHCPv4
clients on a port may be unknown. The DSLAM may also not know the
network portions of the IP addresses that are assigned to its DHCPv4
clients.
The DSLAM gleans IP address or other information from DHCP
negotiations for antispoofing and for other purposes. The
antispoofing itself is done in the fast path. The DSLAM keeps track
of only one list of IP addresses: the list of IP addresses that are
assigned by a DHCPv4 server. Traffic for all other IP addresses is
dropped. If a client starts its data transfer after its DHCPv4
negotiations are gleaned by the DSLAM, 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 Leasequery scenario after a DSLAM loses its
gleaned information (for example, because of reboot).
After a deep analysis, we found that the three existing query types
supported by [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. That
results in increased outage time for DHCPv4 clients.
o result in excessive negative caching consuming lot of resources
under a spoofing attack.
o result in antispoofing being done in the slow path instead of
the fast path.
o do not support an Access Concentrator which periodically uploads
its internal table to some form of stable storage
The deeper analysis, which led to the above conclusions, itself
appears as an Appendix to this document.
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4. Design Goals
The goal of this document is to provide a lightweight mechanism for
an Access Concentrator or other network element to retrieve IP
address binding information available in the DHCPv4 server. The
mechanism should also allow an Access Concentrator to retrieve
consolidated IP address binding information for the entire access
concentrator or for a single connection/circuit.
4.1. Information Acquisition before Data Starts
The existing data driven approach required by [RFC4388] means that
the Leasequeries can only be performed after an Access Concentrator
receives data. To implement antispoofing, packets need to be dropped
until it gets the lease information from DHCPv4 server. If an Access
Concentrator finishes the Leasequeries before it starts receiving
data, then there is no need to drop legitimate packets. In this way,
outage time may be reduced.
4.2. Lessen Negative Caching
If Leasequeries result in negative caches, then that puts additional
overhead on the access concentrator. The negative caches not only
consume precious resources, they also need to be managed. Hence they
should be avoided as much as possible. The Leasequeries should
reduce the need for negative caching as far as possible.
4.3. Antispoofing in 'Fast Path'
If Antispoofing is not done in fast path, it will become a bottleneck
and may lead to denial of service of the access concentrator. The
Leasequeries should make it possible to do antispoofing in fast path.
4.4. Minimize data transmission
It may be that a network element is able to periodically save its
entire list of assigned IP addresses to some form of stable storage.
In this case, it will wish to recover all of the updates to this
information without duplicating the information it has recovered from
its own stable storage.
Bulk Leasequery allows specification of a query-start-time as well as
a query-end-time. Use of query-times allows a network element that
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periodically commits information to stable storage to recover just
what it lost since the last commit.
5. Protocol Overview
The Bulk Leasequery mechanism is modeled on the existing individual
Leasequery protocol in [RFC4388] as well as related work on DHCPv6
Bulk Leasequery [DHCPv6Bulk]. A Bulk Leasequery requestor opens a TCP
connection to a DHCPv4 Server, using the DHCPv4 port 67. Note that
this implies that the Leasequery requestor has server IP address(es)
available via configuration or some other means, and that it has
unicast IP reachability to the DHCPv4 server. No relaying of Bulk
Leasequery messages is specified.
After establishing a connection, the requestor sends a
DHCPBULKLEASEQUERY message over the connection.
The server uses the message type and additional data in the DHCPv4
DHCPBULKLEASEQUERY message to identify any relevant bindings.
In order to support some query types, servers may have to maintain
additional data structures or otherwise be able to locate bindings
that have been requested by the Leasequery requestor.
The Bulk Leasequery mechanism is designed to provide an external
entity with information concerning existing DHCPv4 IPv4 address
bindings managed by the DHCPv4 server. When complete, the DHCPv4
server will send a DHCPLEASEQUERYDONE message. If a connection is
lost while processing a Bulk Leasequery, the Bulk Leasequery must be
retried as there is no provision for determining the extent of data
already received by the requestor for a Bulk Leasequery.
Bulk Leasequery supports queries by MAC address, and Client
Identifier in a way similar to [RFC4388]. The Bulk Leasequery
protocol also adds several new queries.
o Query by Relay Identifier
This query asks a server for the bindings associated with a
specific relay agent; the relay agent is identified by a DUID
carried in a Relay-ID sub-option [RelayId]. Relay agents can
include this sub-option while relaying messages to DHCPv4
servers. Servers can retain the Relay-ID and associate it with
bindings made on behalf of the relay agent's clients. The
bindings returned are only those for DHCPv4 clients with a
currently active binding.
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o Query by Remote ID
This query asks a server for the bindings associated with a
Relay Agent Remote-ID sub-option [RFC3046] value. The bindings
returned are only those for DHCPv4 clients with a currently
active binding.
o Query for All Configured IP Addresses
This query asks a server for information concerning all IP
addresses configured in that DHCPv4 server, by specifying no
other type of query. In this case, the bindings returned are for
all configured IP addresses, whether or not they contain a
currently active binding to a DHCPv4 client, since one point of
this type of query is to update an existing database with
changes after a particular point in time.
Any of the above queries can be qualified by the specification of a
query-start-time or a query-end-time (or both). In the event these
times are used as qualifiers they indicate that a binding should be
included if it changed on or after the query-start-time and on or
before the query-end-time.
In addition, any of the above queries can be qualified by the
specification of a vpn-id option [VpnId] to select the VPN on which
the query should be processed. The vpn-id option is also extended to
allow queries across all available VPNs. By default, only the default
VPN is used to satisfy the query.
6. Interaction Between UDP Leasequery and Bulk Leasequery
Bulk Leasequery can be seen as an extension of the existing UDP
Leasequery protocol [RFC4388]. This section clarifies the
relationship between the two protocols.
Only the DHCPBULKLEASEQUERY request is supported over the Bulk
Leasequery connection. No other DHCPv4 requests are supported. The
Bulk Leasequery connection is not an alternative DHCPv4 communication
option for clients seeking other DHCPv4 services.
Two of the query-types introduced in the UDP Leasequery protocol can
be used in the Bulk Leasequery protocol -- query by MAC address and
query by client-id.
One change in behavior for these existing queries is required when
Bulk Leasequery is used. [RFC4388], in sections 6.1, 6.4.1, and
6.4.2 specifies the use of an associated-ip option in DHCPLEASEACTIVE
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messages in cases where multiple bindings were found. When Bulk
Leasequery is used, this mechanism is not necessary; a server
returning multiple bindings simply does so directly as specified in
this document. The associated-ip option MUST NOT appear in Bulk
Leasequery replies.
The contents of the reply messages are similar between the existing
UDP Leasequery protocol and the Bulk Leasequery protocol, though more
information is returned in the Bulk Leasequery messages and, as
discussed above, the associated-ip option MUST NOT be used.
7. Message and Option Definitions
7.1. Message Framing for TCP
The use of TCP for the Bulk Leasequery protocol permits multiple
messages to be sent from one end of the connection to the other
without requiring a request/response paradigm as does UDP DHCPv4
[RFC2131]. The receiver needs to be able to determine the size of
each message it receives. Two octets containing the message size in
network byte-order are prepended to each DHCPv4 message sent on a
Bulk Leasequery TCP connection. The two message-size octets 'frame'
each DHCPv4 message.
The maximum message size is 65535 octets.
DHCPv4 message framed for TCP:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| message-size | op (1) | htype (1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| hlen (1) | hops (1) | .... |
+---------------+---------------+ +
| |
. remainder of DHCPv4 message,
. from Figure 1 of [RFC2131] .
. .
. (variable) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
message-size the number of octets in the message that
follows, as a 16-bit integer in network
byte-order.
All other fields are as specified in DHCPv4 [RFC2131].
Figure 2: Format of a DHCPv4 message in TCP
The intent in using this format is that code which currently knows
how to deal with sending or receiving a message in [RFC2131] format
will easily be able to deal with the message contained in the TCP
framing.
7.2. New or Changed Options
The existing messages DHCPLEASEUNASSIGNED and DHCPLEASEACTIVE are
used as the value of the dhcp-message-type option to indicate an IP
address which is currently not leased or currently leased to a DHCPv4
client, respectively [RFC4388].
Additional options have also been defined to enable the Bulk
Leasequery protocol to communicate useful information to the
requestor.
7.2.1. dhcp-message-type
The dhcp-message-type option (option 53) from Section 9.6 of
[RFC2132] requires new values. The values of these message types are
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shown below in an extension of the table from Section 9.6 of
[RFC2132]:
Value Message Type
----- ------------
14 DHCPBULKLEASEQUERY
15 DHCPLEASEQUERYDONE
7.2.2. dhcp-message
The dhcp-message option (option 56) from Section 9.9 of [RFC2132]
requires additional definition for use in the context of a
DHCPBULKLEASEQUERY.
The format of the NVT ASCII message in the dhcp-message option is
specified to have the first three characters appear in a constrained
format. The first three characters MUST be numeric (base 10)
characters.
Encoded in these first three characters is the decimal number
corresponding to a variety of status codes defined below.
The motivation for this constraint of the existing dhcp-message
option is to reduce the number of top-level options used by this
document.
The status code returned in the dhcp-message option allows greater
detail to be returned regarding the status of a DHCPBULKLEASEQUERY
request. While specified in the Bulk Leasequery document, this
additional specification of the DHCPv4 dhcp-message option may well
be valuable in other circumstances. In those circumstances its scope
should be explicitly defined.
This option has two possible scopes when used with Bulk Leasequery,
depending on the context in which it appears. It refers to the
information in a single Leasequery reply if the value of the dhcp-
message-type is DHCPLEASEACTIVE or DHCPLEASEUNASSIGNED. It refers to
the message stream related to an entire request if the value of the
dhcp-message-type is DHCPLEASEQUERYDONE.
The code for this option is 56. The length of this option is at least
3 octets.
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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-code | option-len | left-number | middle-number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| right-number | status-message (if any) ... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code 56.
option-len 3 + length of status-message (which may be 0).
left-number NVT ASCII encoded characters representing the
middle-number base-10 value of the status code, taken
right-number from the table below.
status-message An optional NVT ASCII encoded text string
suitable for display to an end user, which
MUST NOT be null-terminated. It SHOULD
start with an NVT ASCII space.
Name status-code Description
---- ----------- -----------
Success 000 Success. Also signaled by absence of
dhcp-message option.
UnspecFail 001 Failure, reason unspecified.
QueryTerminated 002 Indicates that the server is unable to
perform a query or has prematurely terminated
the query for some reason (which should be
communicated in the text message).
MalformedQuery 003 The query was not understood.
NotAllowed 004 The query or request was understood but was
not allowed in this context.
A dhcp-message option MAY appear in the options field of a DHCPv4
message. If the dhcp-message option does not appear, it is assumed
that the operation was successful. The dhcp-message option SHOULD
NOT appear in a message which is successful unless there is some text
string that needs to be communicated to the requestor.
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7.2.3. base-time
The base-time option is the current time the message was created to
be sent by the DHCPv4 server to the requestor of the Bulk Leasequery.
This MUST be an absolute time. All of the other time based options in
the reply message are relative to this time, including the dhcp-
lease-time [RFC2132] and client-last-transaction-time [RFC4388].
This time is in the context of the DHCPv4 server.
This is an integer in network byte order.
The code for this option is TBD. The length of this option is 4
octets.
DHCPv4 Server
Code Len Base Time
+-----+-----+-----+-----+-----+-----+
| TBD | 4 | t1 | t2 | t3 | t4 |
+-----+-----+-----+-----+-----+-----+
7.2.4. start-time-of-state
The start-time-of-state option allows the receiver to determine the
time at which the IP address transitioned into its current state.
This MUST NOT be an absolute time. This MUST NOT be an absolute
number of seconds since Jan 1, 1970. Instead, this MUST be an
integer number of seconds in the past from the time specified in the
base-time option in the same message that the IP address transitioned
into its current state. In the same way that the IP Address Lease
Time option (option 51) encodes a lease time which is a number of
seconds into the future from the time the message was sent, this
option encodes a value which is a number of seconds into the past
from the base-time option included in the same message.
This is an integer in network byte order.
The code for this option is TBD. The length of this option is 4
octets.
Seconds in the past
Code Len from base-time
+-----+-----+-----+-----+-----+-----+
| TBD | 4 | t1 | t2 | t3 | t4 |
+-----+-----+-----+-----+-----+-----+
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7.2.5. query-start-time
The query-start-time option allows the requestor to specify a start
query time to the DHCPv4 server. If specified, only bindings that
have changed on or after the query-start-time should be included in
the response to the query.
This MUST be an absolute time.
This MUST be a time in the context of the DHCPv4 server. In the
absence of information to the contrary, the requestor SHOULD assume
that the time context of the DHCPv4 server is identical to the time
context of the requestor.
It SHOULD NOT be a time in the context of the requestor.
This is an integer in network byte order.
The code for this option is TBD. The length of this option is 4
octets.
DHCPv4 Server
Code Len query-start-time
+-----+-----+-----+-----+-----+-----+
| TBD | 4 | t1 | t2 | t3 | t4 |
+-----+-----+-----+-----+-----+-----+
7.2.6. query-end-time
The query-end-time option allows the requestor to specify an end
query time to the DHCPv4 server. If specified, only bindings that
have changed on or before the query-end-time should be included in
the response to the query.
This MUST be an absolute time.
This MUST be a time in the context of the DHCPv4 server. In the
absence of information to the contrary, the requestor SHOULD assume
that the time context of the DHCPv4 server is identical to the time
context of the requestor.
It SHOULD NOT be a time in the context of the requestor.
This is an integer in network byte order.
The code for this option is TBD. The length of this option is 4
octets.
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DHCPv4 Server
Code Len query-end-time
+-----+-----+-----+-----+-----+-----+
| TBD | 4 | t1 | t2 | t3 | t4 |
+-----+-----+-----+-----+-----+-----+
7.2.7. dhcp-state
The dhcp-state option allows greater detail to be returned than
allowed by the DHCPLEASEACTIVE and DHCPLEASEUNASSIGNED message types.
The code for this option is TBD. The length of this option is 1
octet.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Length | State |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code The suboption code (TBD).
Length The suboption length, 1 octet.
State The State of the IP address.
Value State
----- -----
1 AVAILABLE Address is available to local DHCPv4 server
2 ACTIVE Address is assigned to a DHCPv4 client
3 EXPIRED Lease has expired
4 RELEASED Lease has been released by DHCPv4 client
5 ABANDONED Server or client flagged address as unusable
6 RESET Lease was freed by some external agent
7 REMOTE Address is available to a remote DHCPv4 server
8 TRANSITIONING Address is moving between states
Note that some of these states may be transient and may not appear in
normal use. A DHCPv4 server MUST implement at least the AVAILABLE
and ACTIVE states, and SHOULD implement at least the ABANDONED and
RESET states.
The dhcp-state option SHOULD contain ACTIVE when it appears in a
DHCPLEASEACTIVE message. A DHCPv4 server MAY choose to not send a
dhcp-state option in a DHCPLEASEACTIVE message, and a requestor
SHOULD assume that the dhcp-state is ACTIVE if no dhcp-state option
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appears in a DHCPLEASEACTIVE message.
The reference to local and remote relate to possible use in an
environment that includes multiple servers cooperating to provide an
increased availability solution. In this case, an IP address with
the state of AVAILABLE is available to the local server, while one
with the state of REMOTE is available to a remote server. Usually,
an IP address which is AVAILABLE on one server would be REMOTE on any
remote server. The TRANSITIONING state is also likely to be useful
in multiple server deployments, where sometimes one server must
interlock a state change with one or more other servers. Should a
Bulk Leasequery need to send information concerning the state of the
IP address during this period, it SHOULD use the TRANSITIONING state,
since the IP address is likely to be neither ACTIVE or AVAILABLE.
There is no requirement for the state of an IP address to transition
in a well defined way from state to state. To put this another way,
you cannot draw a simple state transition graph for the states of an
IP address and the requestor of a Leasequery MUST NOT depend on one
certain state always following a particular previous state. In
general, every state can (at times) follow every other state.
7.2.8. data-source
The data-source option contains information about the source of the
data in a DHCPLEASEACTIVE or a DHCPLEASEUNASSIGNED message. It is
used when there are two or more servers who might have information
about a particular IP address binding. Frequently two servers work
together to provide an increased availability solution for the DHCPv4
service, and in these cases, both servers will respond to Bulk
Leasequery requests for the same IP address.
The data contained in this option will allow an external process to
better discriminate between the information provided by each of the
servers servicing this IPv4 address.
The code for this option is TBD. The length of this option is 1
octet.
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0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code The suboption code (TBD).
Length The suboption length, 1 octet.
Flags The Source information for this message.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| MBZ |R|
+-+-+-+-+-+-+-+-+
R: REMOTE flag
remote = 1
local = 0
MBZ: MUST BE ZERO (reserved for future use)
The REMOTE flag is used to indicate where the most recent change of
state (or other interesting change) concerning this IPv4 address took
place. If the value is local, then the change took place on the
server from which this message was transmitted. If the value is
remote, then the change took place on some other server, and was made
known to the server from which this message was transmitted.
If this option was requested and it doesn't appear, the the requestor
SHOULD consider that the data-source was local.
7.2.9. Virtual Subnet Selection Type and Information
All of the (sub)options defined in [VpnId] carry identical payloads,
consisting of a type and additional VSS (Virtual Subnet Selection)
information. The existing table is extended (see below) with a new
type 254 to allow specification of a type code which indicates that
all VPN's are to be used to process the Bulk Leasequery.
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Type VSS Information format:
---- -----------------------
0 NVT ASCII VPN identifier
1 RFC2685 VPN-ID
2-253 Not Allowed
NEW -> 254 All VPN's (wildcard).
255 Global, default VPN.
7.3. Connection and Transmission Parameters
DHCPv4 servers that support Bulk Leasequery SHOULD listen for
incoming TCP connections on the DHCPv4 server port 67.
Implementations MAY offer to make the incoming port configurable, but
port 67 MUST be the default. Requestors SHOULD make TCP connections
to port 67, and MAY offer to make the destination server port
configurable.
This section presents a table of values used to control Bulk
Leasequery behavior, including recommended defaults. Implementations
MAY make these values configurable.
Parameter Default Description
------------------------------------------
BULK_LQ_CONN_TIMEOUT 30 secs Leasequery connection timeout
BULK_LQ_QUERY_TIMEOUT 30 secs Leasequery query timeout
BULK_LQ_MAX_CONNS 10 Max Leasequery TCP connections
BULK_LQ_MAX_CONN_RETRY 60 secs Max Leasequery retry timeout
BULK_LQ_DATA_TIMEOUT 30 secs Leasequery data timeout
8. Requestor Behavior
8.1. Connecting and General Processing
A requestor attempts to establish a TCP connection to a DHCPv4 server
in order to initiate a Leasequery exchange. The requestor SHOULD be
prepared to abandon the connection attempt after
BULK_LQ_CONN_TIMEOUT. If the attempt fails, the requestor MAY retry.
Retries MUST use an exponential backoff timer, increasing the
interval between attempts up to BULK_LQ_MAX_CONN_RETRY.
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If Bulk Leasequery is terminated prematurely by a DHCPLEASEQUERYDONE
with a dhcp-message status-code of QueryTerminated or by the failure
of the connection over which it was being submitted, the requestor
MAY retry the request after the creation of a new connection.
Retries MUST use an exponential backoff timer, increasing the
interval between attempts up to BULK_LQ_MAX_CONN_RETRY.
Messages from the DHCPv4 server come as multiple responses to a
single DHCPBULKLEASEQUERY message. Thus, each DHCPBULKLEASEQUERY
request MUST have a xid (transaction-id) unique on the connection on
which it is sent, and all of the messages which come as a response to
it all contain the same xid as the request. It is the xid which
allows the data-streams of two different DHCPBULKLEASEQUERY requests
to be demultiplexed by the requestor.
A requestor MAY send a DHCPBULKLEASEQUERY request to a DHCPv4 server
and immediately close the transmission side of its TCP connection,
and then read the resulting response messages from the DHCPv4 server.
This is not required, and the usual approach is to leave both sides
of the TCP connection up until at least the conclusion of the Bulk
Leasequery.
8.2. Forming a Bulk Leasequery
Bulk Leasequery is designed to create a connection which will
transfer the state of some subset (or possibly all) of the IP address
bindings to the requestor from DHCPv4 server. The DHCPv4 server
will send all of the requested IPv4 address bindings across this
connection with minimal delay after it receives the request. In this
context, "all IP address binding information" means information about
all IPv4 addresses configured within the DHCPv4 server which meet the
specified query criteria. For some query criteria, this may include
IP address binding information for IP addresses which may not now
have or ever had have an association with a specific DHCPv4 client.
To form the Bulk query, a DHCPv4 request is constructed with a dhcp-
message-type of DHCPBULKLEASEQUERY. The query SHOULD have a dhcp-
parameter-request-list to inform the DHCPv4 server which DHCPv4
options are of interest to the requestor sending the
DHCPBULKLEASEQUERY message. The dhcp-parameter-request-list in a
DHCPBULKLEASEQUERY message SHOULD contain the codes for base-time,
dhcp-lease-time, start-time-of-state, and client-last-transaction-
time.
A DHCPBULKLEASEQUERY request is constructed of one of a series of
primary queries and the optional addition of one or more qualifiers
to those primary queries.
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The possible primary queries are listed below. Each
DHCPBULKLEASEQUERY request MUST consist of only one of these primary
queries.
o Query by MAC address
In a Query by MAC address, the chaddr, htype, and hlen of the
DHCPv4 packet are filled in with the values requested.
o Query by Client-Id
In a Query by Client-Id, the dhcp-client-id option containing
the requested value is included in the DHCPBULKLEASEQUERY
request.
o Query by Remote-Id
In a Query by Remote-Id, the remote-id sub-option of the relay-
agent-information option containing the requested value is
included in the DHCPBULKLEASEQUERY request.
o Query by Relay-Id
In a Query by Relay-Id, the relay-id sub-option [RelayId] of the
relay-agent-information option containing the requested value is
included in the DHCPBULKLEASEQUERY request.
o Query for All Configured IP Addresses
A Query for All Configured IP addresses is signaled by the
absence of any other primary query.
There are three qualifiers which can be applied to any of the above
primary queries. These qualifiers can appear individually or
together in any combination, but only one of each can appear.
o Query Start Time
Inclusion of the query-start-time option specifies that only IP
address bindings which have changed on or after the time specified
in the query-start-time option should be returned.
o Query End Time
Inclusion of the query-end-time option specifies that only IP
address bindings which have changed on or before the time specified
in the query-end-time option should be returned.
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o VPN Id
If no vpn-id option appears in the DHCPBULKLEASEQUERY, the default
VPN is used to search to satisfy the query specified by the
DHCPBULKLEASEQUERY. Using the vpn-id option [VpnId] allows the
requestor to specify a single VPN other than the default VPN. In
addition, the vpn-id option has been extended as part of this
document to allow specification that all configured VPN's be
searched in order to satisfy the query specified in the
DHCPBULKLEASEQUERY.
In all cases, any message returned from a DHCPBULKLEASEQUERY
request containing information about an IP address for other than
the default VPN MUST contain a vpn-id option in the message.
Both of the query-start-time and query-end-time options (if they
appear) MUST be in the time context of the DHCPv4 server to which the
Bulk Leasequery is directed. In the absence of information to the
contrary, the requestor SHOULD assume that the time context on the
DHCPv4 server is identical to the time context on the requestor. In
the event that previous operations have determined that the time
context on the DHCPv4 server to which the Bulk Leasequery is
addressed differs from the time context of the requestor, the time
context of the DHCPv4 server MUST be used.
Use of the query-start-time or the query-end-time options or both can
serve to reduce the amount of data transferred over the TCP
connection by a considerable amount.
If the TCP connection becomes blocked while the requestor is sending
its query, the requestor SHOULD be prepared to terminate the
connection after BULK_LQ_QUERY_TIMEOUT. We make this recommendation
to allow requestors to control the period of time they are willing to
wait before abandoning a connection, independent of notifications
from the TCP implementations they may be using.
8.3. Processing Bulk Replies
The requestor attempts to read a DHCPv4 Leasequery message from the
TCP connection. If the stream of replies becomes blocked, the
requestor SHOULD be prepared to terminate the connection after
BULK_LQ_DATA_TIMEOUT, and MAY begin retry processing if configured to
do so.
A single Bulk Leasequery can and usually will result in a large
number of replies. The requestor MUST be prepared to receive more
than one reply with an xid matching a single DHCPBULKLEASEQUERY
message from a single DHCPv4 server. If the xid in the received
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message does not match an outstanding DHCPBULKLEASEQUERY message, the
requestor MUST close the TCP connection.
If a response message does not contain a DHCPv4 server-identifier
option (option 54), then the server-identifier option from the
previous message should be used. Thus, the DHCPv4 server MUST send
the server-identifier option in the first response message, and MAY
send it in subsequent response message for the same request.
The response messages generated by a DHCPBULKLEASEQUERY request are:
o DHCPLEASEQUERYDONE
A response of DHCPLEASEQUERYDONE indicates that the server has
completed its response to the query, and that no more messages
will be sent in response to the DHCPBULKLEASEQUERY. More details
will sometimes be available in the received dhcp-message option
in the DHCPLEASEQUERYDONE message. If there is no dhcp-message
option in the DHCPLEASEQUERYDONE message, then the query
completed successfully.
Note that a query which returned no data, that is a
DHCPBULKLEASEQUERY request followed by a DHCPLEASEQUERYDONE
response, is considered a successful query in that no errors
occurred during the processing. It is not considered an error
to have no information to return to a DHCPBULKLEASEQUERY
request.
o DHCPLEASEACTIVE
A Bulk Leasequery will generate DHCPLEASEACTIVE messages
containing binding data for bound IP addresses which match the
specified query criteria. The IP address which is bound to a
DHCPv4 client will appear in the ciaddr field of the
DHCPLEASEACTIVE message. The message may contain a non-zero
chaddr, htype, and hlen and possibly additional options.
o DHCPLEASEUNASSIGNED
Some queries will also generate DHCPLEASEUNASSIGNED messages for
IP addresses which match the query criteria. These messages
indicate that the IP address was not currently bound to any
DHCPv4 client. The IP address to which this message refers will
appear in the ciaddr field of the DHCPLEASEUNASSIGNED message.
A DHCPLEASEUNASSGINED message MAY also contain information about
the last DHCPv4 client that was bound to this IP address. The
message may contain a non-zero chaddr, htype, and hlen and
possibly additional options.
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o DHCPLEASEUNKNOWN
The DHCPLEASEUNKNOWN message MUST NOT appear in a response to a
Bulk Leasequery.
The requestor MUST NOT assume that there is any inherent order in the
IP address binding information that is sent in response to a
DHCPBULKLEASEQUERY. While the base-time will tend to increase
monotonically (as it is the current time on the DHCPv4 server), the
actual time that any IP address binding information changed is
unrelated to the base-time.
The DHCPLEASEQUERYDONE message always ends a successful
DHCPBULKLEASEQUERY request and any unsuccessful DHCPBULKLEASEQUERY
requests not terminated by a dropped connection. After receiving
DHCPLEASEQUERYDONE from a server, the requestor MAY close the TCP
connection to that server if no other DHCPBULKLEASEQUERY is
outstanding on that TCP connection.
The DHCPv4 Leasequery protocol [RFC4388] uses the associated-ip
option as an indicator that multiple bindings were present in
response to a single DHCPv4 client based query. For Bulk Leasequery,
a separate message is returned for each binding, and so the
associated-ip option is not used.
8.4. Processing Time Values in Leasequery messages
Bulk Leasequery requests may be made to a DHCPv4 server whose
absolute time may not be synchronized with the local time of the
requestor. Thus, there are at least two time contexts in even the
simplest Bulk Leasequery response, and in the situation where
multiple DHCPv4 servers are queried, the situation becomes even more
complex.
If the requestor of a Bulk Leasequery is saving the data returned in
some form, it has a requirement to store a variety of time values,
and some of these will be time in the context of the requestor and
some will be time in the context of the DHCPv4 server.
When receiving a DHCPLEASEACTIVE or DHCPLEASEUNASSIGNED message from
the DHCPv4 server, the message will contain a base-time option. The
time contained in this base-time option is in the context of the
DHCPv4 server. As such, it is an ideal time to save and use as input
to a DHCPBULKLEASEQUERY in the query-start-time or query-end-time
options, should the requestor need to ever issue a DHCPBULKLEASEQUERY
message using those options as part of the query.
In addition to saving the base-time for possible future use in a
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query-start-time option, the base-time is used as part of the
conversion of the other times in the Leasequery message to values
which are meaningful in the context of the requestor.
The requestor SHOULD use the base-time values received in Bulk
Leasequery messages to develop a value which represents the clock
skew between the DHCPv4 server and the requestor. In theory this
clock skew would simply be the difference between the first base-time
value and the current time on the requestor when the message
containing the base-time value was received. However, there may be
transmission delays at the beginning or end or along the TCP
connection, and so the actual clock skew may not be the same as any
individual difference between a base-time value and the current time
of the requestor.
Moreover, in systems whose clocks are synchronized, perhaps using
NTP, the clock skew will usually be zero, which is not only
acceptable, but desired.
The requestor SHOULD smooth the value which it uses as the clock skew
by continuously examining the instantaneous value developed from the
base-time of each message received from a DHCPv4 server and using
this instantaneous value of clock skew to make small adjustments to
the existing value of the clock skew. Thus, the clock skew will vary
only slowly and one slow message will not completely distort a large
number of future time calculations.
Given the value of the clock skew on the requestor, the requestor
SHOULD bring all of the times in the DHCPLEASEACTIVE and
DHCPLEASEUNASSIGNED messages into the context of the requestor.
Except for the base-time value, the times in the Leasequery message
are all relative to the base-time. These relative times SHOULD first
be converted into absolute times in the context of the DHCPv4 server
using the base-time value. Once this stage is complete, the absolute
times that result SHOULD be brought into the context of the requestor
by applying the calculated clock skew to each of the absolute times.
After all of this processing, the times are in the context of the
requestor.
An alternative might appear to be to leave all of the times in the
context of the DHCPv4 server, and if the requestor is dealing with
only one DHCPv4 server at a time, this is an accurate and effective
approach. However, if the requestor is dealing with DHCPLEASEACTIVE
and DHCPLEASEUNASSIGNED messages from two or more different DHCPv4
servers, then in order to make any sense of them, the times from each
server SHOULD be converted into the time of the requestor.
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Since various transmission and processing delays may occur, a time
converted into the requestor's context may be accurate to only a few
seconds, at best. This is rarely an issue in the larger context of
the use of the information derived from a Bulk Leasequery request.
However, time comparison is an important factor in determining which
update to the address binding information for a particular IPv4
address is the most recent and therefore worth remembering. The next
section discusses the issue of comparing two updates in some detail,
but a key aspect of that comparison is a comparison of the times in
the two messages.
The requestor SHOULD consider times converted into its context as
effectively equivalent if they are within a small number of seconds
of each other. The precise number depends on the particular
implementation involved, but 4 to 8 seconds is probably a good
starting point. Thus, if two times are 3 seconds apart after
conversion to the requestor's context they should be considered the
same for purposes of comparison with each other.
8.5. Querying Multiple Servers
A Bulk Leasequery requestor MAY be configured to attempt to connect
to and query from multiple DHCPv4 servers in parallel. The DHCPv4
Leasequery specification [RFC4388] includes a discussion about
reconciling binding data received from multiple DHCPv4 servers.
In addition, the algorithm in the Section 8.6 should be used.
8.6. Making Sense Out of Multiple Responses Concerning a Single IPv4
Address
Any requestor of an Bulk Leasequery MUST be prepared for multiple
responses to arrive for a particular IPv4 address from multiple
different DHCPv4 servers. The following algorithm SHOULD be used to
decide if the information just received is more up to date (i.e.,
better) than the best existing information. In the discussion below,
the information that is received from a DHCPv4 server about a
particular IPv4 address is termed a "record". The times used in the
algorithm below SHOULD have been converted into the requestor's
context and the time comparisons SHOULD be performed in a manner
consistent with the information in Section 8.4.
o If both the existing and the new record contain client-last-
transaction-time information, the record with the later client-
last-transaction-time is considered better.
o If one of the records contains client-last-transaction-time
information and the other one doesn't, then compare the client-
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last-transaction-time in the record that contains it against the
other record's start-time-of-state. The record with the later
time is considered better.
o If neither record contains client-last-transaction-time
information, compare their start-time-of-state information. The
record with the later start-time-of-state is considered better.
o If none of the comparisons above yield a clear answer as to
which record is later, then compare the value of the REMOTE flag
from the data-source option for each record.
If the values of the REMOTE flag are different between the two
records, the record with the REMOTE flag value of local is
considered better.
The above algorithm does not necessarily determine which record is
better. In the event that the algorithm is inconclusive with regard
to a record which was just received by the requestor, the requestor
SHOULD use additional information in the two records to make a
determination as to which record is better.
8.7. Multiple Queries to a Single Server over One Connection
Bulk Leasequery requestors may need to make multiple queries in order
to recover binding information. A requestor MAY use a single
connection to issue multiple queries to a server willing to support
them. Each query MUST have a unique xid.
A server MAY process more than one query at a time. A server that
will not support more than one query at a time on a single connection
MUST return a DHCPLEASEQUERYDONE message containing a dhcp-message
option with a status-code of NotAllowed to the unsupported queries.
Alternatively, a server that will not support more than one query at
a time on a single connection MAY chose to simply read one query and
only read any subsequent queries after processing of the current
query is complete.
A server that is willing to do so MAY interleave replies to the
multiple queries within the stream of reply messages it sends.
Requestors need to be aware that replies for multiple queries may be
interleaved within the stream of reply messages. Requestors that are
not able to process interleaved replies (based on xid) MUST NOT send
more than one query over a single connection prior to the completion
of the previous query. Requestors should be aware that servers are
not required to process more than one query over a connection at a
time, and that servers are likely to limit the rate at which they
process queries from any one requestor.
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8.7.1. Example
This example illustrates what a series of queries and responses might
look like. This is only an example - there is no requirement that
this sequence must be followed, or that requestors or servers must
support parallel queries.
In the example session, the client sends four queries after
establishing a connection. Query 1 returns no results; query 2
returns 3 messages and the stream of replies concludes before the
client issues any new query. Query 3 and query 4 overlap, and the
server interleaves its replies to those two queries.
Requestor Server
--------- ------
DHCPBULKLEASEQUERY xid 1 ----->
<----- DHCPLEASEQUERYDONE xid 1
DHCPBULKLEASEQUERY xid 2 ----->
<----- DHCPLEASEACTIVE xid 2
<----- DHCPLEASEACTIVE xid 2
<----- DHCPLEASEACTIVE xid 2
<----- DHCPLEASEQUERYDONE xid 2
DHCPBULKLEASEQUERY xid 3 ----->
DHCPBULKLEASEQUERY xid 4 ----->
<----- DHCPLEASEACTIVE xid 4
<----- DHCPLEASEACTIVE xid 4
<----- DHCPLEASEACTIVE xid 3
<----- DHCPLEASEACTIVE xid 4
<----- DHCPLEASEUNASSIGNED xid 3
<----- DHCPLEASEACTIVE xid 4
<----- DHCPLEASEACTIVE xid 3
<----- DHCPLEASEQUERYDONE xid 3
<----- DHCPLEASEACTIVE xid 4
<----- DHCPLEASEQUERYDONE xid 4
8.8. Closing Connections
Either the requestor or DHCPv4 server MAY close the TCP connection at
any time. The requestor MAY choose to retain the connection if it
intends to issue additional queries or if other queries are currently
using the connection. Note that this requestor behavior does not
guarantee that the connection will be available for additional
queries: the server might decide to close the connection based on its
own configuration.
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9. Server Behavior
9.1. Accepting Connections
Servers that implement DHCPv4 Bulk Leasequery listen for incoming TCP
connections. Port numbers are discussed in Section 7.3. Servers
MUST be able to limit the number of currently accepted and active
connections. The value BULK_LQ_MAX_CONNS SHOULD be the default;
implementations MAY permit the value to be configurable. Connections
SHOULD be accepted and, if the number of connections is over
BULK_LQ_MAX_CONNS, they SHOULD be closed immediately.
Servers MAY restrict Bulk Leasequery connections and
DHCPBULKLEASEQUERY messages to certain requestors. Connections not
from permitted requestors SHOULD be closed immediately, to avoid
server connection resource exhaustion. Servers MAY restrict some
requestors to certain query types. Servers MAY reply to queries that
are not permitted with the DHCPLEASEQUERYDONE message with a dhcp-
message status of NotAllowed, or MAY simply close the connection.
If the TCP connection becomes blocked while the server is accepting a
connection or reading a query, it SHOULD be prepared to terminate the
connection after an BULK_LQ_QUERY_TIMEOUT. We make this
recommendation to allow servers to control the period of time they
are willing to wait before abandoning an inactive connection,
independent of the TCP implementations they may be using.
9.2. Replying to a Bulk Leasequery
If the connection becomes blocked while the server is attempting to
send reply messages, the server SHOULD be prepared to terminate the
TCP connection after BULK_LQ_DATA_TIMEOUT.
Every Bulk Leasequery request MUST be terminated by sending a final
DHCPLEASEQUERYDONE message if such a message can be sent. The
DHCPLEASEQUERYDONE message MUST have a dhcp-message status if the
termination was other than successful, and SHOULD NOT contain a
dhcp-message status if the termination was successful.
If the DHCPv4 server encounters an error during processing of the
DHCPBULKLEASEQUERY message, either during initial processing or later
during the message processing, it SHOULD send a DHCPLEASEQUERYDONE
containing a status dhcp-message option. It MAY close the connection
after this error is signaled, but that is not required.
If the server does not find any bindings satisfying a query, it MUST
send a DHCPLEASEQUERYDONE. It SHOULD NOT include a dhcp-message
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option with a Success status unless there is a useful string to
include in the dhcp-message option. Otherwise, the server sends each
binding's data in a DHCPLEASEACTIVE or DHCPLEASEUNASSIGNED message.
The response to a DHCPBULKLEASEQUERY may involve examination of
multiple DHCPv4 IP address bindings maintained by the DHCPv4 server.
The Bulk Leasequery protocol does not require any ordering of the IP
addresses returned in DHCPLEASEACTIVE or DHCPLEASEUNASSIGNED
messages.
A Bulk Leasequery response MUST contain no more than one message for
each configured IP address in the DHCPv4 server. In addition, a Bulk
Leasequery may well take significant time between the beginning and
end of the processing of all of the messages required to satisfy the
Bulk Leasequery query. During this time, the state of some of the IP
addresses sent early in the response may change prior to the
completion of the entire response to the Bulk Leasequery. This is
normal and expected -- there is no requirement for the entire
response to a Bulk Leasequery to represent an instantaneous snapshot
of the state of the IP address bindings of a DHCPv4 server. Quite
the contrary -- as the cursor moves through the IP addresses in
whatever order is convenient to the DHCPv4 server, the state of IP
addresses already examined can change and a DHCPv4 server MUST NOT
try to examine IP addresses already scanned in an attempt to "keep
up" with the ongoing state changes of all of the IP addresses. To do
so would make it difficult to meet the requirement to send only one
message per IP address in response to a Bulk Leasequery and would
also make it difficult to know when to finish the Bulk Leasequery.
If the ciaddr, yiaddr, or siaddr is non-zero in a DHCPBULKLEASEQUERY
request, the request must be terminated immediately by a
DHCPLEASEQUERYDONE message with a dhcp-message status of
MalformedQuery.
Any DHCPBULKLEASEQUERY which has more than one of the following
primary query types specified MUST be terminated immediately by a
DHCPLEASEQUERYDONE message with a dhcp-message status code of
NotAllowed.
The allowable queries in a DHCPBULKLEASEQUERY message are processed
as follows. Note that the descriptions of the primary queries below
must constrained by the actions of any of the three qualifiers
described subsequently as well.
The following table discusses how to process the various queries.
For information on how to identify the query, see the information in
Section 8.2.
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o Query by MAC address
Every IP address which has a current binding to a DHCPv4 client
which matches the chaddr, htype, and hlen in the
DHCPBULKLEASEQUERY request MUST be returned in a DHCPLEASEACTIVE
message.
o Query by Client-Id
Every IP address which has a current binding to a DHCPv4 client
which matches the client-id option in the DHCPBULKLEASEQUERY
request MUST be returned in a DHCPLEASEACTIVE message.
o Query by Remote-Id
Every IP address which has a current binding to a DHCPv4 client
which matches the remote-id sub-option of the relay-agent-
information option in the DHCPBULKLEASEQUERY request MUST be
returned in a DHCPLEASEACTIVE message.
o Query by Relay-Id
Every IP address which has a current binding to a DHCPv4 client
which matches the relay-id sub-option of the relay-agent-
information option in the DHCPBULKLEASEQUERY request MUST be
returned in a DHCPLEASEACTIVE message.
o Query for All Configured IP Addresses
A Query for All Configured IP addresses is signaled by the
absence of any other primary query. That is, if there is no
value in the chaddr, hlen, htype, no client-id option, no
remote-id sub-option or relay-id sub-option of the relay-agent-
information option, then the request is a query for information
concerning all configured IP addresses. In this case, every
configured IP address which has a current binding to a DHCPv4
client MUST be returned in a DHCPLEASEACTIVE message. In
addition, every configured IP address which does not have a
current binding to a DHCPv4 client MUST be returned in a
DHCPLEASEUNASSIGNED message.
In this form of query, each configured IP address MUST be
returned at most one time. If the absence of qualifiers which
restrict the number of IP addresses returned, every configured
IP address MUST be returned exactly once.
There are three qualifiers which can be applied to any of the above
primary queries. These qualifiers can appear individually or
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together in any combination, but only one of each can appear.
o Query Start Time
If a query-start-time option appears in the DHCPBULKLEASEQUERY
request, only IP address bindings which have changed on or after
the time specified in the query-start-time option should be
returned.
o Query End Time
If a query-end-time option appears in the DHCPBULKLEASEQUERY
request, only IP address bindings which have changed on or before
the time specified in the query-end-time option should be returned.
o VPN Id
If no vpn-id option appears in the DHCPBULKLEASEQUERY, the default
VPN is used to satisfy the query. A vpn-id option [VpnId] value
other than the wildcard value (254) allows the requestor to specify
a single VPN other than the default VPN. In addition, the vpn-id
option has been extended as part of this document to allow
specification of a type 254 which indicates that all configured
VPN's be searched in order to satisfy the primary query.
In all cases, if the information returned in a DHCPLEASEACTIVE or
DHCPLEASEUNASSIGNED message is for other than the default a vpn-id
option MUST appear in the packet.
The query-start-time and query-end-time qualifiers are used to
constrain the amount of data returned by a Bulk Leasequery request by
returning only IP addresses whose address bindings have changed in
some way during the time window specified by the query-start-time and
query-end-time.
A DHCPv4 server SHOULD consider an address binding to have changed
during a specified time window if either the client-last-
transaction-time or the start-time-of-state of the address binding
changed during that time window.
A DHCPv4 server MAY always compare the address binding information
for an IP address against a time window if it follows the following
guidelines. If there is no query-start-time, then the DHCPv4 server
MUST assume the query-start-time is equivalent to a time prior to any
time that resides in any IP address binding. If there is no query-
end-time, the DHCPv4 server MUST assume that the query-end-time is
equivalent to a time that is later than any time that resides in any
IP address binding.
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Even if the query-start-time or query-end-time option value is being
used to limit the amount of data flow from the DHCPv4 server to the
requestor, there is no requirement placed on the DHCPv4 server to
return address binding data in any order and certainly not in any
order based on time.
When the DHCPv4 server has no additional information to send to the
requestor, it will send a DHCPLEASEQUERYDONE message.
9.3. Building a Single Reply for Bulk Leasequery
The DHCPv4 Leasequery [RFC4388] specification describes the initial
construction of DHCPLEASEQUERY reply messages using the
DHCPLEASEACTIVE and DHCPLEASEUNASSIGNED message types in Section
6.4.2. All of the reply messages in Bulk Leasequery are similar to
the reply messages for an IP address query. Message transmission and
framing for TCP is described in this document in Section 7.1.
[RFC2131] and [RFC4388] specify that every response message MUST
contain the server-identifier option. However, that option will be
the identical for every response from a particular DHCPBULKLEASEQUERY
request. Thus, the DHCPv4 server MUST include the server-identifier
option in the first message sent in response to a DHCPBULKLEASEQUERY.
It MAY include the server-identifier in later messages as well, but
there is no requirement for it to do so.
The message type of DHCPLEASEACTIVE or DHCPLEASEUNASSIGNED is based
on the value of the dhcp-state option. If the dhcp-state option
value is ACTIVE, then the message type is DHCPLEASEACTIVE, otherwise
the message type is DHCPLEASEUNASSIGNED.
In addition to the basic message construction described in [RFC4388],
the following guidelines exist:
1. If the dhcp-state option code appears in the dhcp-parameter-
request-list, the DHCPv4 server SHOULD include a dhcp-state
option whose value corresponds most closely to the state held
by the DHCPv4 server for the IP address associated with this
reply. If the state is ACTIVE and the message being returned
in DHCPLEASEACTIVE then the DHCPv4 server MAY choose to not
send the dhcp-state option. The requestor SHOULD assume that
any DHCPLEASEACTIVE message arriving without a requested dhcp-
state option has a dhcp-state of ACTIVE.
2. If the base-time option code appears in the dhcp-parameter-
request-list, the DHCPv4 server MUST include a base-time
option, which is the current time in the DHCPv4 server's
context and the time from which the start-time-of-state, dhcp-
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lease-time, client-last-transaction-time, and other duration-
style times are based upon.
3. If the start-time-of-state option code appears in the dhcp-
parameter-request-list, the DHCPv4 server MUST include a
start-time-of-state option whose value represents the time at
which the dhcp-state option's state became valid.
4. If the dhcp-lease-time option code appears in the dhcp-
parameter-request-list, the DHCPv4 server MUST include a dhcp-
lease-time option for any state that has a time-out value
associated with it, and not just appear in a DHCPLEASEACTIVE
message. Thus, the EXPIRED state which is sent in a
DHCPLEASEUNASSIGNED message would have a dhcp-lease-time option
in the message if the EXPIRED state represented a grace-period
and would be changing state after the grace-period expired.
5. If the data-source option code appears in the dhcp-parameter-
request-list, the DHCPv4 server MUST include the data-source
option in any situation where any of the bits would be non-
zero. Thus, in the absence of the data-source option, the
assumption is that all of the flags were zero.
6. If the client-last-transaction-time option code appears in the
dhcp-parameter-request-list, The DHCPv4 server MUST include the
client-last-transaction-time option in any situation where the
information is available.
7. If there is a dhcp-parameter-request-list in the initial
DHCPBULKLEASEQUERY request, then it should be used for all of
the replies generated by that request. Some options can be
sent from a DHCPv4 client to the server or from the DHCPv4
server to a DHCPv4 client. Option 125 is such an option. If
the option code for one of these options appears in the dhcp-
parameter-request-list, it SHOULD result in returning the value
of the option sent by the DHCPv4 client to the server if one
exists.
Note that there may be other requirements for a reply to a
DHCPBULKLEASEQUERY request discussed in Section 9.2.
9.4. Multiple or Parallel Queries
As discussed in Section 8.3, requestors may want to leverage an
existing connection if they need to make multiple queries. Servers
MAY support reading and processing multiple queries from a single
connection. A server MUST NOT read more query messages from a
connection than it is prepared to process simultaneously.
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This MAY be a feature that is administratively controlled. Servers
that are able to process queries in parallel SHOULD offer
configuration that limits the number of simultaneous queries
permitted from any one requestor, in order to control resource use if
there are multiple requestors seeking service.
9.5. Closing Connections
The server MAY close its end of the TCP connection after sending its
last message, a DHCPLEASEQUERYDONE message in response to a query.
Alternatively, the server MAY retain the connection and wait for
additional queries from the requestor. The server SHOULD be prepared
to limit the number of connections it maintains, and SHOULD be
prepared to close idle connections to enforce the limit.
The server MUST close its end of the TCP connection if it encounters
an error sending data on the connection. The server MUST close its
end of the TCP connection if it finds that it has to abort an in-
process request. A server aborting an in-process request SHOULD
attempt to signal that to its requestors by using the QueryTerminated
status code in the dhcp-message option in a DHCPLEASEQUERYDONE
message, including a message string indicating details of the reason
for the abort. If the server detects that the requesting end of the
connection has been closed, the server MUST close its end of the
connection after it has finished processing any outstanding requests.
The server MUST send a DHCPLEASEQUERYDONE message at the end of the
data returned from a Bulk Leasequery request.
10. Security Considerations
The "Security Considerations" section of [RFC2131] details the
general threats to DHCPv4. The DHCPv4 Leasequery specification
[RFC4388] describes recommendations for the Leasequery protocol,
especially with regard to relayed LEASEQUERY messages, mitigation of
packet-flooding DOS attacks, restriction to trusted requestors, and
use of IPsec [RFC4301].
The use of TCP introduces some additional concerns. Attacks that
attempt to exhaust the DHCPv4 server's available TCP connection
resources, such as SYN flooding attacks, can compromise the ability
of legitimate requestors to receive service. Malicious requestors
who succeed in establishing connections, but who then send invalid
queries, partial queries, or no queries at all also can exhaust a
server's pool of available connections. We recommend that servers
offer configuration to limit the sources of incoming connections,
that they limit the number of accepted connections and the number of
in-process queries from any one connection, and that they limit the
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period of time during which an idle connection will be left open.
11. IANA Considerations
IANA is requested to assign the following new values for this
document. See Section 7.2 for details.
1. A dhcp-message-type of 14 for DHCPBULKLEASEQUERY.
2. A dhcp-message-type of 15 for DHCPLEASEQUERYDONE.
3. An option code of TBD for base-time.
4. An option code of TBD for start-time-of-state.
5. An option code of TBD for query-start-time.
6. An option code of TBD for query-end-time.
7. An option code of TBD for data-source.
8. An option code of TBD for dhcp-state.
9. Values for dhcp-state:
State
-----
1 AVAILABLE
2 ACTIVE
3 EXPIRED
4 RELEASED
5 ABANDONED
6 RESET
7 REMOTE
8 TRANSITIONING
10.Values for status code in a constrained dhcp-message option
(option 53):
Name status-code
---- -----------
Success 000
UnspecFail 001
QueryTerminated 002
MalformedQuery 003
NotAllowed 004
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11.Addtional type field values for the Virtual Subnet Selection
Type and Information [VpnId]:
Type VSS Information format:
0 NVT ASCII VPN identifier
1 RFC2685 VPN-ID
2-253 Not Allowed
NEW -> 254 All VPN's. (wildcard)
255 Global, default VPN.
12. Acknowledgements
This draft is a collaboration between the authors of draft-dtv-dhc-
dhcpv4-bulk-leasequery-00.txt and draft-kkinnear-dhc-dhcpv4-bulk-
leasequery-00.txt. Both documents acknowledged that significant text
as well as ideas were borrowed in whole or in part from the DHCPv6
Bulk Leasequery draft [DHCPv6Bulk].
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997.
[RFC2132] Alexander, S., Droms, R., "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
[RFC3046] Patrick, M., "DHCP Relay Agent Information Option", RFC
3046, January 2001.
[RFC4301] Kent, S., K. Seo, "Security Architecture for the Internet
Protocol", RFC4301, December 2005.
[RFC4388] Woundy, R., K. Kinnear, "Dynamic Host Configuration
Protocol (DHCP) Leasequery", RFC 4388, February 2006.
[RelayId] Stapp, M., "The DHCPv4 Relay Agent Identifier Suboption",
draft-ietf-dhc-relay-id-suboption-04.txt, September 2008.
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[VpnId] Kinnear, K., R. Johnson, M. Stapp and J. Kumarasamy, "Virtual
Subnet Selection Options for DHCPv4 and DHCPv6" draft-ietf-dhc-
vpn-option-09.txt, July 2008.
13.2. Informative References
[RFC951] Croft, B., Gilmore, J., "Bootstrap Protocol (BOOTP)", RFC
951, September 1985.
[RFC1542] Wimer, W., "Clarifications and Extensions for the Bootstrap
Protocol", RFC 1542, October 1993.
[RFC4614] Duke, M., R. Braden, W. Eddy, and E. Blanton, "A Roadmap
for Transmission Control Protocol (TCP) Specification Documents",
RFC 4614, September 2006.
[DHCPv6Bulk] Stapp, M., "DHCPv6 Bulk Leasequery", draft-ietf-dhc-
dhcpv6-bulk-leasequery-04.txt, October 2008.
14. Authors' Addresses
Kim Kinnear
Cisco Systems
1414 Massachusetts Ave.
Boxborough, Massachusetts 01719
Phone: (978) 936-0000
EMail: kkinnear@cisco.com
Bernie Volz
Cisco Systems
1414 Massachusetts Ave.
Boxborough, Massachusetts 01719
Phone: (978) 936-0000
EMail: volz@cisco.com
Neil Russell
Cisco Systems
1414 Massachusetts Ave.
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Boxborough, Massachusetts 01719
Phone: (978) 936-0000
EMail: nrussell@cisco.com
Mark Stapp
Cisco Systems
1414 Massachusetts Ave.
Boxborough, Massachusetts 01719
Phone: (978) 936-0000
EMail: mjs@cisco.com
Ramakrishna Rao DTV
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/
Pavan Kurapati
Infosys Technologies Ltd.
44 Electronics City, Hosur Road
Bangalore 560 100
India
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EMail: pavan_kurapati@infosys.com
URI: http://www.infosys.com/
15. Full Copyright Statement
Copyright (C) The IETF Trust (2008).
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.
16. 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
ietf-ipr@ietf.org.
17. Acknowledgment
Funding for the RFC Editor function is provided by the IETF
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Administrative Support Activity (IASA).
18. Appendix -- Why a New Leasequery is Required
The three existing query types supported by [RFC4388] do not provide
effective and efficient antispoofing for the scenario discussed in
Section 3.
o Query by Client Identifier
Query by Client Identifier is not possible because the DSLAM would
need to glean the client-identifier. This is not possible since if
we are using a Leasequery, it is because the gleaned information was
lost. On the other hand, we can query by client-identifier when
client sends a DHCPv4 request, but then there may not be any need for
Leasequery as such -- regular gleaning may be enough.
o Query by IP Address
[RFC4388] suggests that it is preferable to use Query by IP Address
when getting downstream traffic.
Query by IP address is not very useful because because downstream
traffic may not exist for the clients on a DSL port. (In most
Internet applications, downstream traffic exists only when a client
sends upstream traffic). In other words, the client will be denied
service until it gets downstream traffic, which may never come.
Query by IP address may be used for upstream traffic. Then whenever
an upstream packet comes whose IP address is unknown to the DSLAM, a
lease query may be initiated. A related question is what to do with
that upstream traffic itself until lease query response comes? If
the traffic is dropped, we may be dropping legitimate traffic. If
the traffic is forwarded, we may be forwarding spoofed packets. Once
the lease response comes, subsequent traffic is handled depending on
the response. If a DHCPLEASEACTIVE response comes, the DSLAM will
accept the traffic. If a DHCPLEASEUNASSIGNED response comes, the
DSLAM will drop the traffic corresponding to the IP address. If a
DHCPLEASEUNKNOWN response comes the DSLAM may drop the traffic
corresponding to the IP address but will have to periodically send
the lease query for that IP address again (additional overhead). The
process is triggered whenever an unknown IP address comes.
Note that the DSLAM needs to keep track of 4 lists of IP addresses:
(1) 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 got DHCPLEASEUNKNOWN
responses; (4) All other IP addresses.
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This approach may be acceptable if only legitimate traffic is
received. Consider the case when someone sends packets that uses
spoofed IP addresses. In that case, lease response will be
DHCPLEASEUNASSIGNED or DHCPLEASEUNKNOWN. [RFC4388] suggests usage of
negative caching in this regard (which involves additional
resources).
In a spoofing type of attack, negative caching information may grow
considerably if attacker varies the source IP address. For each such
new source IP address, traffic will come to slow path, a new lease
query needs to be initiated, response will be processed, and negative
caching needs to be done. That will mean using many resources for
negative caching.
[RFC4388] suggests that if the DSLAM knows the network 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 queries may be
avoided. But as indicated before, that information may not always be
available to DSLAMs.
Effectively, antispoofing support involves considerable slow path
processing and considerable resources tied for negative caching.
[RFC4388] says that DHCPv4 server should be protected from being
flooded with too many Leasequery requests and DSLAM also should not
send too many lease query messages at a time. This would mean that
legitimate requestors may be excessively delayed getting their
information in the face of antispoofing attacks.
It is concluded that antispoofing is neither effective nor efficient
with this query type.
o Query by MAC Address
Query by MAC address can also be used in a way similar to query by IP
address described above. Indeed, query by MAC address may be better
than query by IP address in one sense because of the possible
presence of the associated-ip option in lease responses. (Note that
associated-ip option does not appear in responses for query by IP
address). With associated-ip option DSLAM can get information not
only about the IP address/MAC address that triggered the Leasequery
but also about other IP addresses that are associated with the
original MAC address. That way, when traffic that uses the other IP
addresses comes along, DSLAM is already prepared to deal with them.
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
query by IP address. For a query by MAC address, only two types of
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responses are possible: DHCPLEASEUNKNOWN and DHCPLEASEACTIVE;
DHCPLEASEUNASSIGNED is not supported. This is particularly
troublesome when a DHCPv4 server indeed has definitive information
that no IP addresses are associated with the specified MAC address in
the Leasequery, but it is forced to respond with DHCPLEASEUNKNOWN
instead of DHCPLEASEUNASSIGNED. As we have seen above, unlike
DHCPLEASEUNASSIGNED, DHCPLEASEUNKNOWN requires periodic querying with
DHCPv4 server, an additional overhead.
Moreover, query by MAC address also shares all other issues we
discussed above for query by IP address.
We conclude that existing Leasequery types are not appropriate to
achieve effective and efficient antispoofing in the environment
discussed.
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