DHCPv6 Active Leasequery

The DHCPv6 protocol specifies a mechanism for the assignment of IPv6 address and configuration information to IPv6 nodes. IPv6 Prefix Delegation for DHCPv6 (PD) specifies a mechanism for DHCPv6 delegation of IPv6 prefixes and related data. DHCPv6 servers maintain authoritative information including binding information for delegated IPv6 prefixes. Requirements exist for external entities to keep up to date on the correspondence between DHCPv6 clients and their bindings. These requirements often stem from regulatory requirements placed on service providers by governmental agencies. These entities need to keep up with the current binding activity of the DHCPv6 server. Keeping up with these binding activity is termed "active" leasequery. The DHCPv6 Bulk Leasequery capability can be used to recover useful information from a DHCPv6 server when some external entity starts up. This entity could be one which is directly involved in the DHCPv6 client - server transactions (e.g., a relay agent), or it could be an external process which needs information present in the DHCPv6 server's lease state database. The Active Leasequery capability documented here is designed to allow an entity not directly involved in DHCPv6 client - server transactions to nevertheless keep current with the state of the DHCPv6 lease state information in real-time.

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 . DHCPv6 terminology is defined in . Terminology specific to DHCPv6 Active Leasequery can be found below: "Absolute Time" A 32-bit quantity containing the number of seconds since January 1, 2000. "Active Leasequery" Keeping up to date in real-time (or near real-time) with DHCPv6 binding activity. "Bulk Leasequery" Requesting and receiving the existing DHCPv6 binding information in an efficient manner. "catch-up information, catch-up phase" If a DHCPv6 Active Leasequery requestor sends OPTION_LQ_START_TIME option in a ACTIVELEASEQUERY message, the DHCPv6 server will attempt to send the requestor the information that changed since the time specified in the OPTION_LQ_START_TIME option. The binding information sent to satisfy this request is the catch-up information, and the period while it is being sent is the catch-up phase. "clock skew" The difference between the absolute time on a DHCPv6 server and the absolute time on the system where a requestor of an Active or Bulk Leasequery is executing is termed the "clock skew" for that Active or Bulk Leasequery connection. It is not absolutely constant but is likely to vary only slowly. While it is easy to think that this can be calculated precisely after one packet is received by a requestor from a DHCPv6 server, a more accurate value is derived from continuously examining the instantaneous value developed from each packet received from a DHCPv6 server and using it to make small adjustments to the existing value held in the requestor. "Transaction ID" An opaque value used to match responses with queries initiated by an Active Leasequery client.

The Active Leasequery mechanism is modeled on the existing DHCPv6 Bulk Leasequery ; most differences arise from the long term nature of the TCP connection required for Active Leasequery. In addition, a DHCPv6 server which supports Active Leasequery MUST support Bulk Leasequery as well. An Active Leasequery client opens a TCP connection to a DHCPv6 Server, using the DHCPv6 port 547. Note that this implies that the Leasequery client has server IP address(es) available via configuration or some other means, and that it has unicast IP reachability to the DHCPv6 server. No relaying for Active Leasequery is specified. After establishing a connection, the client sends an ACTIVELEASEQUERY message over the connection. In response, the server sends updates to the requestor using LEASEQUERY-REPLY and LEASEQUERY-DATA messages. This response procedure is identical to , except that in case of Active Leasequery server sends updates whenever some activity occurs to change binding state - thus the need for long lived connection. Active Leasequery is designed to provide continuous updates of DHCPv6 IPv6 binding activity to an external entity. Active Leasequery has features which allow this external entity to lose its connection and then reconnect and receive the latest information concerning any IPv6 bindings changed while it was not connected. These capabilities are designed to allow the Active Leasequery requestor to efficiently become current with respect to the lease state database after it has been restarted or the machine on which it is running has been reinitialized. It is easy to define a protocol which works when the requestor is always connected to the DHCPv6 server. Since that isn't sufficiently robust, much of the mechanism in this document is designed to deal efficiently with situations that occur when the Active Leasequery requestor becomes disconnected from the DHCPv6 server from which it is receiving updates and then becomes reconnected to that server. Central to this approach, if the Active Leasequery requestor loses service, it is allowed to specify the time of its most recent update in a subsequent Active Leasequery request and the DHCPv6 server will determine whether or not data was missed while the Active Leasequery requestor was not connected. The DHCPv6 server processing the Active Leasequery request may limit the amount of data saved, and methods exist for the DHCPv6 server to inform the Active Leasequery requestor that more data was missed than could be saved. In this situation, the Active Leasequery requestor would issue a Bulk Leasequery to recover information not available through an Active Leasequery. DHCPv6 servers are not required to keep any data corresponding to data missed on a Active Leasequery connection, but will typically choose to keep data corresponding to some recent activity available for subsequent queries by a DHCPv6 Active Leasequery client whose connection was temporarily interrupted. An Active Leasequery requestor would typically use Bulk Leasequery to initialize its database with all current data when that database contains no binding information. In addition, it would use Bulk Leasequery to recover missed information in the event that its connection with the DHCPv6 server was lost for a longer time than the DHCPv6 server would keep track of the specific changes to the IPv6 binding information. The messages sent by the server in response to an Active Leasequery request SHOULD be identical to the messages sent by the server to a Bulk Leasequery request regarding the way the data is encoded into the Active Leasequery responses. In addition, the actions taken by the Active Leasequery requestor to interpret the responses to an Active Leasequery request SHOULD be identical to the way that the requestor interprets the responses to a Bulk Leasequery request. Thus, the handling of OPTION_CLIENT_DATA and additional options discussed in the Bulk Leasequery specification are to be followed when implementing Active Leasequery.

Active Leasequery can be seen as an extension of the Bulk Leasequery protocol . The format of packets returned to an Active Leasequery requestor are identical to that defined for the Bulk Leasequery protocol . Applications which employ Active Leasequery to keep a database up to date with respect to the DHCPv6 server's lease state database will usually use an initial Bulk Leasequery to bring their database into equivalence with that of the DHCPv6 server, and then use Active Leasequery to keep that database current with respect to the DHCPv6 server's lease state database. There are several differences between the Active and Bulk Leasequery protocols. Active Leasequery defines a new message (ACTIVELEASEQUERY) to send Active Leasequery request to DHCPv6 server. An Active Leasequery connection sends all available updates to the requestor, based on OPTION_LQ_QUERY option (see ). An Active Leasequery connection does not ever "complete", though the DHCPv6 server may drop the connection for a variety of reasons associated with some sort of exception condition.

This document extends to the capabilities of DHCPv6 Bulk Leasequery protocol by defining new options. More details about these options are specified in .

The use of TCP for the Active Leasequery protocol permits one or more DHCPv6 messages to be sent at a time. The receiver needs to be able to determine how large each message is. The same message framing technique used for DHCPv6 Bulk Leasequery is used for Active Leasequery as well. The intent in using the same format is that code which currently knows how to deal with a message returned from DHCPv6 Bulk Leasequery will be able to deal with the message held inside of the TCP framing.

The LEASEQUERY-REPLY message is defined in . The LEASEQUERY-DATA and LEASEQUERY-DONE messages are defined in . In a Active Leasequery exchange, a single LEASEQUERY-REPLY message is used to indicate the success or failure of a query, and to carry data that do not change in the context of a single query and answer, such as the Server-ID and Client-ID options. If a query is successful, only a single LEASEQUERY-REPLY message MUST appear. If the server is returning binding data, the LEASEQUERY-REPLY also contains the first client's binding data in an OPTION_CLIENT_DATA option. Additional binding data is returned using LEASEQUERY-DATA message as explained in DHCPv6 Bulk Leasequery . In case of failure query, single LEASEQUERY-REPLY message is returned without any binding data.

The new message type (ACTIVELEASEQUERY) is designed to assist requestor keeping up to date in real-time (or near real-time) with DHCPv6 bindings. It asks the server to return DHCPv6 bindings activity that occurs subsequent to the receipt of the Active Leasequery request. An ACTIVELEASEQUERY request MUST contain a transaction-id, and that transaction-id MUST BE locally unique to the TCP connection to the DHCPv6 server. While sending Active Leasequery request, requestor MAY include OPTION_LQ_START_TIME option in ACTIVELEASEQUERY request. In this case, DHCPv6 server returns all the bindings changed on or after the OPTION_LQ_START_TIME. If the requestor is interested in receiving all binding updates from DHCPv6 server, it MUST NOT include OPTION_LQ_QUERY option in ACTIVELEASEQUERY message. But if the requestor is only interested in specific binding updates, it MAY include OPTION_LQ_QUERY option along with query-types defined in and . Other DHCPv6 options used in LEASEQUERY message (as specified in ) can also be used in ACTIVELEASEQUERY request.

New options (OPTION_LQ_BASE_TIME, OPTION_LQ_START_TIME and OPTION_LQ_END_TIME) are defined as an extension to DHCPv6 Bulk Leasequery . DHCPv6 server sends OPTION_LQ_BASE_TIME option in Active or Bulk Leasequery response if requestor ask for the same in Active or Bulk Leasequery request. OPTION_LQ_START_TIME can be used in Active or Bulk Leasequery request made to DHCPv6 server. OPTION_LQ_END_TIME can be used in Bulk Leasequery request made to DHCPv6 server. The reply messages for Active Leasequery uses the options defined in , and .

The OPTION_LQ_BASE_TIME option is the current time the message was created to be sent by the DHCPv6 server to the requestor of the Active or 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 OPTION_CLT_TIME . This time is in the context of the DHCPv6 server who placed this option in a message. This is an unsigned integer in network byte order. The code for this option is TBD. The length of this option is 4 octets.

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_BASE_TIME | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | base-time | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code OPTION_LQ_BASE_TIME (TBD). option-len 4. base-time DHCPv6 Server Base Time.

The OPTION_LQ_START_TIME option specifies a query start time to the DHCPv6 server. If specified, only bindings that have changed on or after the OPTION_LQ_START_TIME should be included in the response to the query. The requestor MUST determine the OPTION_LQ_START_TIME using lease information it has received from the DHCPv6 server. This MUST be an absolute time in the DHCPv6 server's context (see ). Typically (though this is not a requirement) the OPTION_LQ_START_TIME option will contain the value most recently received in a OPTION_LQ_BASE_TIME option by the requestor, as this will indicate the last successful communication with the DHCPv6 server. This is an unsigned integer in network byte order. The code for this option is TBD. The length of this option is 4 octets.

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_START_TIME | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | query-start-time | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code OPTION_LQ_START_TIME (TBD). option-len 4. query-start-time DHCPv6 Server Query Start Time.

The OPTION_LQ_END_TIME option specifies a query end time to the DHCPv6 server. If specified, only bindings that have changed on or before the OPTION_LQ_END_TIME should be included in the response to the query. This option MAY be used in Bulk Leasequery request. But it MUST NOT be used in Active Leasequery request. The requestor MUST determine the OPTION_LQ_END_TIME based on lease information it has received from the DHCPv6 server. This MUST be an absolute time in the context of the DHCPv6 server. In the absence of information to the contrary, the requestor SHOULD assume that the time context of the DHCPv6 server is identical to the time context of the requestor (see ). This is an unsigned integer in network byte order. The code for this option is TBD. The length of this option is 4 octets.

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_END_TIME | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | query-end-time | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code OPTION_LQ_END_TIME (TBD). option-len 4. query-end-time DHCPv6 Server Query End Time.

Active Leasequery uses the same port configuration as DHCPv6 Bulk Leasequery . It also uses the other transmission parameters (BULK_LQ_DATA_TIMEOUT and BULK_LQ_MAX_CONNS) as defined in . This section presents a table of values used to control Active Leasequery behavior, including recommended defaults. Implementations MAY make these values configurable. However, configuring too-small timeout values may lead to harmful behavior both to this application as well as to other traffic in the network. As a result, timeout values smaller than the default values are NOT RECOMMENDED.

Parameter Default Description ---------------------------------------------------------------------- ACTIVE_LQ_RCV_TIMEOUT 120 secs Active Leasequery receive timeout ACTIVE_LQ_SEND_TIMEOUT 120 secs Active Leasequery send timeout ACTIVE_LQ_IDLE_TIMEOUT 60 secs Active Leasequery idle timeout

While the information communicated by a DHCPv6 Bulk Leasequery is taken directly from the DHCPv6 server's lease state database, the information communicated by an Active Leasequery is real-time information. As such, it is the information which is currently associated with a particular binding in the DHCPv6 server's lease state database. This is of significance, because if the Active Leasequery requestor runs slowly or the requestor disconnects from the DHCPv6 server and then reconnects with a OPTION_LQ_START_TIME (signalling a catch-up operation), the information communicated to the Active Leasequery requestor is only the most current information from the DHCPv6 server's lease state database. The requestor of an Active Leasequery MUST NOT assume that every lease state change is communicated across an Active Leasequery connection. Even if the Active Leasequery requestor remains connected, the DHCPv6 server is only required to transmit information about a binding that is current when the packet is created and handed off to the TCP stack to send to the requestor. If the TCP connection blocks and the DHCPv6 server is waiting to send information down the connection, when the connection becomes available to be written the DHCPv6 server MAY create the packet to send at this time. The current state of the binding will be sent, and any transition in state or other information that occurred while the TCP connection was blocked will be lost. Thus, the Active Leasequery protocol does not allow the requestor to build a complete history of every activity on every lease. An effective history of the important state changes for a lease can be created if the parameters of the DHCPv6 server are tuned to take into account the requirements of an Active Leasequery requestor. For instance, the period after the expiration or release of a binding could be configured long enough (say several minutes, well more than the receive timeout), so that an Active Leasequery requestor would never miss any changes in the binding.

A Requestor attempts to establish a TCP connection to a DHCPv6 Server in order to initiate a Active Leasequery exchange. If the attempt fails, the Requestor MAY retry. If an Active Leasequery is terminated prematurely by a LEASEQUERY-DONE with a DHCPv6 status code (carried in an OPTION_STATUS_CODE option) 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. Messages from the DHCPv6 server come as multiple responses to a single ACTIVELEASEQUERY message. Thus, each ACTIVELEASEQUERY request MUST have an xid (transaction-id) unique on the connection on which it is sent, and all of the messages which come as a response to it contain the same xid as the request. It is the xid which allows the data-streams of two or more different ACTIVELEASEQUERY requests to be de-multiplexed by the requestor. A requestor MAY send a ACTIVELEASEQUERY request to a DHCPv6 server and immediately close the transmission side of its TCP connection, and then read the resulting response messages from the DHCPv6 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 Active Leasequery.

The Active Leasequery is designed to create a long lived connection between the requestor and the DHCPv6 server processing the active query. The DHCPv6 server will send binding information back across this connection with minimal delay after it learns of the binding information. It will learn about bindings either because it makes the bindings itself or because it has received information about a binding from another server. To form the Active Leasequery, a DHCPv6 request is constructed with a message type of ACTIVELEASEQUERY. The DHCPv6 request MUST contain a transaction-id, and that transaction-id MUST BE locally unique to the TCP connection to the DHCPv6 server. An important capability of the Active Leasequery is the ability of the requestor to specify that some recent data be sent immediately to the requestor in parallel with the transmission of the ongoing binding information in more or less real time. This capability is used in order to allow an Active Leasequery requestor to recover missed information in the event that it temporarily loses connectivity with the DHCPv6 server processing a previous Active Leasequery. Note that until all of the recent data (catch-up data) has been received, the requestor MUST NOT keep track of the base-time (OPTION_LQ_BASE_TIME) received in Leasequery reply messages to use later in a subsequent Active Leasequery request. This capability is enabled by the transmission of a 4 octet OPTION_LQ_BASE_TIME option with each Leasequery reply sent as the result of a previous Active Leasequery. The requestor will typically keep track of the highest base-time received from a particular DHCPv6 server over an Active Leasequery connection, and in the event that the requestor finds it necessary (for whatever reason) to reestablish an Active Leasequery connection to that DHCPv6 server, the requestor will place this highest base-time value into a OPTION_LQ_START_TIME option in the new Active Leasequery request. If the requestor doesn't wish to request an update of information missed when it was not connected to the DHCPv6 server, then it does not include the OPTION_LQ_START_TIME option in the Active Leasequery request. If the TCP connection becomes blocked or stops being writable while the requestor is sending its query, the requestor SHOULD be prepared to terminate the connection after BULK_LQ_DATA_TIMEOUT. We make this recommendation to allow requesters 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.

The Requestor attempts to read a DHCPv6 LEASEQUERY-REPLY message from the TCP connection. If the stream of replies becomes blocked, the Requestor SHOULD be prepared to terminate the connection after ACTIVE_LQ_RCV_TIMEOUT, and MAY begin retry processing if configured to do so. The requestor examines the LEASEQUERY-REPLY message, and determines how to proceed. Message validation rules are specified in DHCPv6 Leasequery and DHCPv6 Bulk Leasequery . If the reply contains an DHCPv6 status code (carried in an OPTION_STATUS_CODE option), the requestor follows the recommendations in . Note that an Active Leasequery request specifically requests the DHCPv6 server to create a long-lived connection which may not have data transferring continuously during its lifetime. Therefore the DHCPv6 server will send a LEASEQUERY-DATA message without binding data (OPTION_CLIENT_DATA) every ACTIVE_LQ_IDLE_TIMEOUT seconds (default 60) in order for the requestor to know that the connection remains alive. This approach is followed only when connection is idle (i.e. server has no binding data to send). During normal binding data exchange, receiving of LEASEQUERY-DATA message by requestor itself signifies that connection is active. Note that the default for ACTIVE_LQ_RCV_TIMEOUT is 120 seconds, twice the value of the ACTIVE_LQ_IDLE_TIMEOUT's default of 60 seconds which drives the DHCPv6 server to send messages. Thus ACTIVE_LQ_RCV_TIMEOUT controls how sensitive the requestor is to be to delays by the DHCPv6 server in sending updates or LEASEQUERY-DATA messages. A single Active Leasequery can and usually will result in a large number of replies. The Requestor MUST be prepared to receive more than one reply with transaction-ids matching a single ACTIVELEASEQUERY message from a single DHCPv6 server. An Active Leasequery has two regimes -- during the catch-up phase, if any, and after any catch-up phase. During the catch-up phase (if one exists), the data returned in the OPTION_LQ_BASE_TIME option in a LEASEQUERY-REPLY or LEASEQUERY-DATA message may appear to be ordered, but the most recent change in the lease state data being returned is not related to the OPTION_LQ_BASE_TIME option value in the messages. Another way to say this is that the ordering of the updates sent by the DHCPv6 server during the catch-up phase is independent of the ordering in the changes in the lease state data. The OPTION_LQ_BASE_TIME option from messages during this phase MUST NOT be saved and used in a subsequent ACTIVELEASEQUERY message's OPTION_LQ_START_TIME option as it does not represent the extent of progress of the catch-up activity. After the catch-up phase, or during the entire series of messages received as the response to a Active Leasequery request with no OPTION_LQ_START_TIME (and therefore no catch-up phase), the OPTION_LQ_BASE_TIME option of the most recent message SHOULD be saved as a record of the most recent time that data was received. This base-time (in the context of the DHCPv6 server) can be used in a subsequent Active Leasequery message's OPTION_LQ_START_TIME after a loss of the Active Leasequery connection. The LEASEQUERY-DONE message MAY unilaterally terminate a successful Active Leasequery request which is currently in progress in the event that the DHCPv6 server determines that it cannot continue processing a ACTIVELEASEQUERY request. For example, when a server is requested to shut down it SHOULD send a LEASEQUERY-DONE message with a DHCPv6 status code of QueryTerminated and include OPTION_LQ_BASE_TIME option in the message. This SHOULD be the last message on that connection, and once the message has been transmitted, the server should close the connection. After receiving LEASEQUERY-DONE with a QueryTerminated status from a server, the Requestor MAY close the TCP connection to that server.

If the Active Leasequery was requested with a OPTION_LQ_START_TIME, the DHCPv6 server will attempt to send information about all bindings that changed since the time specified in the OPTION_LQ_START_TIME. This is the catch-up phase of the Active Leasequery processing. The DHCPv6 server MAY also begin immediate updates over the same connection of real-time binding information changes. Thus, the catch-up phase may run in parallel with the normal updates generated by the Active Leasequery request. A DHCPv6 server MAY keep only a limited amount of time ordered information available to respond to an Active Leasequery request containing a OPTION_LQ_START_TIME. Thus, it is possible that the time specified in the OPTION_LQ_START_TIME represents a time not covered by the time ordered information kept by the DHCPv6 server. If this should occur, and there is not enough data saved in the DHCPv6 server to satisfy the request specified by the OPTION_LQ_START_TIME option, the DHCPv6 server will reply immediately with a LEASEQUERY-REPLY message with a DHCPv6 status code of DataMissing with a base-time option equal to the server's current time. This will signal the end of the catch-up phase, and the only updates that will subsequently be received on this connection are the real-time updates from the Active Leasequery request. If there is enough data saved to satisfy the request, then LEASEQUERY-REPLY (with OPTION_STATUS_CODE of Success or reply without OPTION_STATUS_CODE option) and LEASEQUERY-DATA messages will begin arrive from the DHCPv6 server. Some of these messages will be related to the OPTION_LQ_START_TIME request and be part of the catch-up phase. Some of these messages will be real-time updates of binding changes taking place in the DHCPv6 server. In general, there is no way to determine the source of each message. Until the catch-up phase is complete, the latest base-time value received from a DHCPv6 server processing an Active Leasequery request cannot be reset from the incoming messages because to do so would compromise the ability to recover lost information if the Active Leasequery were to terminate prior to the completion of the catch-up phase. The requestor will know that the catch-up phase is complete when the DHCPv6 server will transmit a LEASEQUERY-DATA message with the DHCPv6 status code of CatchUpComplete. Once this message is transmitted, all additional LEASEQUERY-DATA messages will relate to real-time ("new") binding changes in the DHCPv6 server. As discussed in , the requestor SHOULD keep track of the latest base-time option value received over a particular connection, to be used in a subsequent Active Leasequery request -- but only if the catch-up phase is complete. Prior to the completion of the catch-up phase, if the connection should go away or if the requestor receives a LEASEQUERY-DONE message, then when it reconnects it MUST use the base-time value from the previous connection and not any base-time value received from the recently closed connection. In the event that there was enough data available to the DHCPv6 server to begin to satisfy the request implied by the OPTION_LQ_START_TIME option, but during the processing of that data the server found that it was unable to continue (perhaps there was barely enough, the connection is very slow, and the aging algorithm causes the saved data to become unavailable) the DHCPv6 server will terminate the catch-up phase of processing immediately by sending a LEASEQUERY-DATA message with a DHCPv6 status code of DataMissing and with a base-time option of the current time. The requestor MUST NOT assume that every individual state change of every binding during the period from the time specified in the OPTION_LQ_START_TIME and the present is replicated in an Active Leasequery reply message. The requestor MAY assume that at least one Active Leasequery reply message will exist for every binding which had one or more changes of state during the period specified by the OPTION_LQ_START_TIME and the current time. The last message for each binding will contain the state at the current time, and there may be one or more messages concerning a single binding during the catch-up phase of processing. If a binding changed state multiple times during the time that the requestor was not connected (that is, during the time from the OPTION_LQ_START_TIME and the present), then only the current binding information will be sent during the catch-up phase. However, the requestor MUST NOT assume that every intermediate state change that occurred during the period from the OPTION_LQ_START_TIME to the present will be represented by an individual Leasequery message. If the LEASEQUERY-REPLY or LEASEQUERY-DATA message containing a DHCPv6 status code of DataMissing is received and the requestor is interested in keeping its database up to date with respect to the current state of bindings in the DHCPv6 server, then the requestor SHOULD issue a Bulk Leasequery request to recover the information missing from its database. This Bulk Leasequery request should include a OPTION_LQ_START_TIME, set to be the same as its OPTION_LQ_START_TIME previously included in the ACTIVELEASEQUERY responses from the DHCPv6 server, and a OPTION_LQ_END_TIME equal to the OPTION_LQ_BASE_TIME returned by the DHCPv6 server in the LEASEQUERY-REPLY or LEASEQUERY-DATA message with the DHCPv6 status code of DataMissing. In the event that the requestor receives a LEASEQUERY-REPLY or LEASEQUERY-DATA message with a DHCPv6 status code of DataMissing, it is a reasonable assumption that it is interested in keeping its database up to date with respect to the DHCPv6 server's internal binding database or it would not have included the OPTION_LQ_START_TIME in the ACTIVELEASEQUERY message. Typically, the requestor would have one connection open to a DHCPv6 server for a Active Leasequery request and possibly one additional connection open for a Bulk Leasequery request to the same DHCPv6 server to fill in the data that might have been missed prior to the initiation of the Active Leasequery. The Bulk Leasequery connection would typically run to completion and be closed, leaving one Active Leasequery connection open to a single DHCPv6 server. Alternatively, both requests could be issued over a single connection.

Active or Bulk Leasequery requests may be made to a DHCPv6 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 Active or Bulk Leasequery response. If the requestor of a Active or 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 DHCPv6 server. When receiving a Active or Bulk Leasequery reply message from the DHCPv6 server, the message will contain a OPTION_LQ_BASE_TIME option. The time contained in this OPTION_LQ_BASE_TIME option is in the context of the DHCPv6 server. As such, it is an ideal time to save and use as input to an Active or Bulk Leasequery message in the OPTION_LQ_START_TIME or OPTION_LQ_END_TIME option, should the requestor need to ever issue an Active or Bulk Leasequery message using these option as part of a later query, since these option requires a time in the context of the DHCPv6 server. In addition to saving the OPTION_LQ_BASE_TIME for possible future use in OPTION_LQ_START_TIME or OPTION_LQ_END_TIME option, the OPTION_LQ_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. In systems whose clocks are synchronized, perhaps using NTP, the clock skew will usually be zero, which is not only acceptable, but desired.

These examples illustrate what a series of queries and responses might look like. These are only examples -- there are no requirement that these sequence must be followed.

This example illustrates the message flows in case DHCPv6 server identifies that it can not accept and/or process Active Leasequery request from the client. This could be because of various reasons (i.e. UnknownQueryType, MalformedQuery, NotConfigured, NotAllowed).

Client Server ------ ------ ACTIVELEASEQUERY xid 1 -----> <----- LEASEQUERY-REPLY xid 1 (w/error)

This example illustrates the message flows in case DHCPv6 server identifies that it does not have enough data saved to satisfy the request specified by the OPTION_LQ_START_TIME option. In this case the DHCPv6 server will reply immediately with a LEASEQUERY-REPLY message with a DHCPv6 status code of DataMissing with a base-time option equal to the server's current time. This will signal the end of the catch-up phase, and the only updates that will subsequently be received on this connection are the real-time updates from the Active Leasequery request.

Client Server ------ ------ ACTIVELEASEQUERY xid 2 -----> <----- LEASEQUERY-REPLY xid 2 (w/error) <----- LEASEQUERY-DATA xid 2 <----- LEASEQUERY-DATA xid 2 <----- LEASEQUERY-DATA xid 2

This example illustrates the message flows in case of successful query processing by DHCPv6 server. In this case the DHCPv6 server will reply immediately with a LEASEQUERY-REPLY message (with OPTION_STATUS_CODE of Success or reply without OPTION_STATUS_CODE option), followed by binding data in LEASEQUERY-DATA messages. In case, DHCPv6 server wants to abort in-process request and terminate the connection due to some reason, it sends LEASEQUERY-DONE with error code present in OPTION_STATUS_CODE option.

Client Server ------ ------ ACTIVELEASEQUERY xid 3 -----> <----- LEASEQUERY-REPLY xid 3 <----- LEASEQUERY-DATA xid 3 <----- LEASEQUERY-DATA xid 3 <----- LEASEQUERY-DATA xid 3 <----- LEASEQUERY-DATA xid 3 <----- LEASEQUERY-DONE xid 3 (w/error)

The Requestor or DHCPv6 Leasequery server MAY close its end of the TCP connection at any time. The Requestor MAY choose to retain the connection if it intends to issue additional queries. Note that this client 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.

A DHCPv6 server which supports Active Leasequery MUST support DHCPv6 Bulk Leasequery as well.

Servers that implement DHCPv6 Active Leasequery listen for incoming TCP connections. Approach used in accepting (or rejecting) the client connection is same as specified in DHCPv6 Bulk Leasequery .

The DHCPv6 Leasequery specification describes the initial construction of LEASEQUERY-REPLY messages. Use of the LEASEQUERY-REPLY and LEASEQUERY-DATA messages to carry multiple bindings is described in DHCPv6 Bulk Leasequery . Message transmission and framing for TCP is described in . 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 ACTIVE_LQ_SEND_TIMEOUT. This timeout governs how much congestion the DHCPv6 server is prepared to tolerate over any Active Leasequery connection. The default is two minutes, which means that if more than two minutes goes by without the requestor reading enough information to unblock the TCP connection, the DHCPv6 server will drop the TCP connection. If the DHCPv6 server encounters an error during initial processing of the ACTIVELEASEQUERY message, it SHOULD send a LEASEQUERY-REPLY message containing an error code of some kind in a DHCPv6 status code option. It SHOULD close the connection after this error is signalled. If the DHCPv6 server encounters an error during later processing of the ACTIVELEASEQUERY message, it SHOULD send a LEASEQUERY-DONE containing an error code of some kind in a DHCPv6 status code option. It SHOULD close the connection after this error is signalled. If the server finds any bindings satisfying a query, it sends each binding's data in a reply message. The first reply message is a LEASEQUERY-REPLY. The binding data is carried in an OPTION_CLIENT_DATA option, as specified in . The server returns subsequent bindings in LEASEQUERY-DATA messages, which can avoid redundant data (such as the requestor's Client-ID). Every reply to a Active Leasequery request MUST contain the information specified in replies to a DHCPv6 Bulk Leasequery request . If an Active Leasequery or Bulk Leasequery request contains OPTION_LQ_BASE_TIME option code present in OPTION_ORO, the DHCPv6 server MUST include OPTION_LQ_BASE_TIME option in every reply for this request. The value for base-time option is current absolute time in the DHCPv6 server's context. If an Active Leasequery request contains a OPTION_LQ_START_TIME option, it indicates that the requestor would like the DHCPv6 server to send it not only messages that correspond to DHCPv6 binding activity that occurs subsequent to the receipt of the Active Leasequery request, but also messages that correspond to DHCPv6 binding activity that occurred prior to the Active Leasequery request. If OPTION_LQ_END_TIME option appears in a Active Leasequery request, the DHCPv6 server should send a LEASEQUERY-REPLY message with a DHCPv6 status code of MalformedQuery and terminate the connection. In order to implement a meaningful response to this query, the DHCPv6 server MAY keep track of the binding activity and associate changes with particular base-time values from the messages. Then, when requested to do so by a Active Leasequery request containing a OPTION_LQ_START_TIME option, the DHCPv6 server can respond with replies for all binding activity occurring on that OPTION_LQ_START_TIME or later times. These replies based on the OPTION_LQ_START_TIME MAY be interleaved with the messages generated due to current binding activity. Once the transmission of the DHCPv6 Leasequery messages associated with the OPTION_LQ_START_TIME option are complete, a LEASEQUERY-DATA message MUST be sent with a DHCPv6 status code value of CatchUpComplete. The DHCPv6 server SHOULD, but is not required to, keep track of a limited amount of previous binding activity. The DHCPv6 server MAY choose to only do this in the event that it has received at least one Active Leasequery request in the past, as to do so will almost certainly entail some utilization of resources which would be wasted if there are no Active Leasequery clients for this DHCPv6 server. The DHCPv6 server SHOULD make the amount of previous binding activity it retains configurable. There is no requirement on the DHCPv6 server to retain this information over a server restart (or even to retain such information at all). Unless there is an error or some requirement to cease processing a Active Leasequery request yielding a LEASEQUERY-DONE message, such as a server shutdown, there will be no LEASEQUERY-DONE message at the conclusion of the Active Leasequery processing because that processing will not conclude but will continue until either the client or the server drops the connection.

Requesters may want to use 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. Typically, a requestor of a Active Leasequery would not need to send a second Active Leasequery while the first is still active. However, sending an Active Leasequery and a Bulk Leasequery over the same connection would be possible and reasonable. But it is RECOMMENDED to use different connection in case of parallel Active and Bulk Leasequeries. 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 requesters seeking service.

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 clients by using the QueryTerminated status code in the DHCPv6 status code option in a LEASEQUERY-DONE message. If the server detects that the client end has been closed, the server MUST close its end of the connection after it has finished processing any outstanding requests from the client. 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 "Security Considerations" section of details the general threats to DHCPv6. The DHCPv6 Leasequery specification describes recommendations for the Leasequery protocol, especially with regard to relayed Leasequery messages, mitigation of packet-flooding denial-of-service (DoS) attacks, restriction to trusted clients, and use of IPsec . The use of TCP introduces some additional concerns. Attacks that attempt to exhaust the DHCPv6 server's available TCP connection resources, such as SYN flooding attacks, can compromise the ability of legitimate clients to receive service. Malicious clients 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 period of time during which an idle connection will be left open. There are two specific issues regarding Active Leasequery security that deserve explicit mention. The first is preventing information that Active Leasequery can provide from reaching clients who are not authorized to receive such information. The second is ensuring that authorized clients of the Active Leasequery capability receive accurate information from the Server (and that this information is not disrupted in transit). To prevent information leakage to unauthorized clients Servers SHOULD restrict Active Leasequery connections and ACTIVELEASEQUERY messages to certain requestors, either through explicit configuration of the Server itself or by employing external network elements to provide such restrictions. In particular, the typical DHCPv6 client SHOULD NOT be allowed to receive a response to an Active Leasequery request, and some technique MUST exist to allow prevention of such access in any environment where Active Leasequery is deployed. Connections not from permitted requestors SHOULD be closed immediately, to avoid server connection resource exhaustion or alternatively, simply not be allowed to reach the server at all. Servers SHOULD have the capability to restrict certain requestors to certain query types. Servers MAY reply to queries that are not permitted with the LEASEQUERY-DONE message with a status-code option status of NotAllowed, or MAY simply close the connection. To prevent disruption and malicious corruption of Active Leasequery data flows between the server and authorized clients these data flows SHOULD transit only secured networks. These data flows are typically infrastructure oriented, and there is usually no reason to have them flowing over networks where such attacks are likely. In the rare cases where these data flows might need to be sent through unsecured networks, they MUST sent over connections secured through means external to the DHCPv4/DHCPv6 server and its client(s) (e.g., through VPN's). Authentication for DHCP Messages MUST NOT be used to attempt to secure transmission of the messages described in this document.

IANA is requested to assign new DHCPv6 Option Codes in the registry maintained in http://www.iana.org/assignments/dhcpv6-parameters: OPTION_LQ_BASE_TIME OPTION_LQ_START_TIME OPTION_LQ_END_TIME IANA is requested to assign new values in the registry of DHCPv6 Status Codes maintained in http://www.iana.org/assignments/dhcpv6-parameters: DataMissing CatchUpComplete IANA is requested to assign value for the following new DHCPv6 Message type in the registry maintained in http://www.iana.org/assignments/dhcpv6-parameters: ACTIVELEASEQUERY

Many of the ideas in this document were originally proposed by Kim Kinnear, Bernie Volz, Mark Stapp and John Brzozowski. Many of the concept and content, present in this document, are based on DHCPv4 Active Leasequery.