Internet Engineering Task Force (IETF) D. Raghuvanshi Request for Comments: 7653 K. Kinnear Updates: 5460 D. Kukrety Category: Standards Track Cisco Systems, Inc. ISSN: 2070-1721 October 2015
DHCPv6 Active Leasequery
Abstract
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) has been extended with a Leasequery capability that allows a requestor to request information about DHCPv6 bindings. That mechanism is limited to queries for DHCPv6 binding data updates prior to the time the DHCPv6 server receives the Leasequery request. Continuous update of an external requestor with Leasequery data is sometimes desired. This document expands on the DHCPv6 Leasequery protocol and allows for active transfer of real-time DHCPv6 binding information data via TCP. This document also updates DHCPv6 Bulk Leasequery (RFC 5460) by adding new options.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7653.
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Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
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Table of Contents
1. Introduction ....................................................4 2. Terminology .....................................................4 3. Protocol Overview ...............................................6 4. Interaction between Active Leasequery and Bulk Leasequery .......8 5. Extension to DHCPv6 Bulk Leasequery .............................8 6. Message and Option Definitions ..................................9 6.1. Message Framing for TCP ....................................9 6.2. Messages ...................................................9 6.2.1. ACTIVELEASEQUERY ....................................9 6.2.2. STARTTLS ...........................................10 6.2.3. Response Messages ..................................10 6.3. Options ...................................................10 6.3.1. OPTION_LQ_BASE_TIME ................................10 6.3.2. OPTION_LQ_START_TIME ...............................11 6.3.3. OPTION_LQ_END_TIME .................................12 6.4. Connection and Transmission Parameters ....................12 7. Information Communicated by Active Leasequery ..................13 8. Requestor Behavior .............................................14 8.1. General Processing ........................................14 8.2. Initiating a Connection ...................................14 8.3. Forming an Active Leasequery ..............................15 8.4. Processing Active Replies .................................16 8.4.1. Processing Replies from a Request Containing an OPTION_LQ_START_TIME ...............................18 8.5. Processing Time Values in Leasequery Messages .............20 8.6. Examples ..................................................21 8.6.1. Query Failure ......................................21 8.6.2. Data Missing on Server .............................21 8.6.3. Successful Query ...................................21 8.7. Closing Connections .......................................22 9. Server Behavior ................................................22 9.1. Accepting Connections .....................................22 9.2. Rejecting Connections .....................................24 9.3. Replying to an Active Leasequery ..........................24 9.4. Multiple or Parallel Queries ..............................26 9.5. Closing Connections .......................................26 10. Security Considerations .......................................27 11. IANA Considerations ...........................................28 12. References ....................................................28 12.1. Normative References .....................................28 12.2. Informative References ...................................29 Acknowledgments ...................................................30 Authors' Addresses ................................................30
The DHCPv6 protocol [RFC3315] specifies a mechanism for the assignment of IPv6 address and configuration information to IPv6 nodes. IPv6 Prefix Delegation for DHCPv6 [RFC3633] 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 entities need to keep up with the current binding activity of the DHCPv6 server. Keeping up with this binding activity is termed "active" leasequery.
The DHCPv6 Bulk Leasequery [RFC5460] capability can be used to recover useful information from a DHCPv6 server when some external entity starts up. This entity could be one that is directly involved in the DHCPv6 client-server transactions (e.g., a relay agent), or it could be an external process that 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.
This document updates DHCPv6 Bulk Leasequery [RFC5460] by adding new options, as described in Section 6.2.1. For DHCPv6 servers supporting Bulk Leasequery and not Active Leasequery, Section 9.2 specifies the mechanism to reject incoming Active Leasequery requests.
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].
DHCPv6 terminology is defined in [RFC3315]. Terminology specific to DHCPv6 Active Leasequery can be found below:
o absolute time
A 32-bit unsigned quantity containing the number of seconds since midnight (UTC), January 1, 2000, modulo 2^32.
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o Active Leasequery
Keeping up to date in real time (or near real time) with DHCPv6 binding activity.
o Bulk Leasequery
Requesting and receiving information about all or some of the existing DHCPv6 binding information in an efficient manner, as defined by [RFC5460].
o blocked TCP connection
A TCP connection is considered blocked if the underlying TCP transport will not accept new messages to be sent without blocking the thread that is attempting to send the message.
o binding change/update
Any change in the DHCPv6 binding state. This also includes expiration or deletion of the binding.
o catch-up information
If a DHCPv6 Active Leasequery requestor sends an OPTION_LQ_START_TIME option in an 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.
o catch-up phase
The period while catch-up information is being sent is the catch- up phase.
o 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 message is received by a requestor from a DHCPv6 server, a more accurate value is derived from continuously examining the instantaneous value developed from each message received from a DHCPv6 server
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and using it to make small adjustments to the existing value held in the requestor.
o DHCPv6 binding state
Data stored on the DHCPv6 server related to binding.
o requestor
The node that sends LEASEQUERY messages to one or more servers to retrieve information on the bindings for a client.
o transaction-id
An opaque value used to match responses with queries initiated by an Active Leasequery requestor.
The Active Leasequery mechanism is modeled on the existing DHCPv6 Bulk Leasequery [RFC5460]; most differences arise from the long-term nature of the TCP [RFC7414] connection required for Active Leasequery. A DHCPv6 server that supports Active Leasequery MUST support Bulk Leasequery [RFC5460] as well.
An Active Leasequery requestor opens a TCP connection to a DHCPv6 server, using the DHCPv6 port 547. 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 DHCPv6 server. No relaying for Active Leasequery is specified.
After establishing a connection, the requestor 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 similar to the procedure specified in [RFC5460], except that in the case of Active Leasequery, the server sends updates whenever some activity occurs to change the binding state -- thus the need for a long-lived connection. Additionally, the Active Leasequery server SHOULD provide a mechanism to control which data is allowed to be included in the OPTION_CLIENT_DATA messages sent to the requestor. See Section 9.3.
Active Leasequery has features that 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.
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These features 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 that 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 reconnects 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 data was missed (i.e., not all data could be saved). In this situation, the Active Leasequery requestor should issue a Bulk Leasequery [RFC5460] to recover information not available through an Active Leasequery.
DHCPv6 servers are not required to keep any data corresponding to data missed on an Active Leasequery connection but will typically choose to keep data corresponding to some recent activity available for subsequent queries by a DHCPv6 Active Leasequery requestor whose connection was temporarily interrupted. In other words, DHCPv6 servers supporting catch-up are required to have some mechanism to keep/save historic information of bindings.
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
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discussed in the Bulk Leasequery specification [RFC5460] are to be followed when implementing Active Leasequery, with the exception that a server responding to an Active Leasequery request SHOULD be able to be configured to prevent specific data items from being included in the OPTION_CLIENT_DATA option even if they were requested by inclusion in the OPTION_ORO option.
4. Interaction between Active Leasequery and Bulk Leasequery
Active Leasequery is an extension of the Bulk Leasequery protocol [RFC5460]. The format of messages returned to an Active Leasequery requestor is identical to that defined for the Bulk Leasequery protocol [RFC5460].
Applications that employ Active Leasequery to keep a database up to date with respect to the DHCPv6 server's lease state database should 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 requests to the DHCPv6 server. An Active Leasequery connection sends all available updates to the requestor, based on the OPTION_LQ_QUERY option (see Section 6.2.1).
An Active Leasequery connection does not ever "complete", though the DHCPv6 server can close the connection for a variety of reasons associated with some sort of exception condition.
This document extends the capabilities of the DHCPv6 Bulk Leasequery protocol [RFC5460] by defining new options (OPTION_LQ_BASE_TIME, OPTION_LQ_START_TIME, and OPTION_LQ_END_TIME). The DHCPv6 server sends the OPTION_LQ_BASE_TIME option in a Bulk Leasequery response if the requestor asked for the same in the Bulk Leasequery request. OPTION_LQ_START_TIME and OPTION_LQ_END_TIME can be used in a Bulk Leasequery request made to the DHCPv6 server. More details about these options are specified in Section 6.3.
The use of TCP for the Active Leasequery protocol permits one or more DHCPv6 messages to be sent in response to a single Active Leasequery request. The receiver needs to be able to determine how large each message is. The same message framing technique used for DHCPv6 Bulk Leasequery [RFC5460] is used for Active Leasequery as well.
The intent in using the same format is that code that currently knows how to deal with a message returned from DHCPv6 Bulk Leasequery [RFC5460] will be able to deal with the message held inside of the TCP framing.
When using Transport Layer Security (TLS), once TLS negotiation completes, the connection will be encrypted and is now protected from eavesdropping, and normal Active Leasequery messages are sent and received using the TLS application data protocol services (see Section 10 of [RFC5246]).
The new message type (ACTIVELEASEQUERY) is designed for keeping the requestor up to date in real time (or near real time) with DHCPv6 bindings. It asks the server to return DHCPv6 binding 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 on the TCP connection on which it is sent to the DHCPv6 server.
When sending an ACTIVELEASEQUERY request, the requestor MAY include the OPTION_LQ_START_TIME option in the ACTIVELEASEQUERY request. In this case, the 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 the DHCPv6 server, it MUST NOT include the OPTION_LQ_QUERY option in the ACTIVELEASEQUERY message. But if the requestor is only interested in specific binding updates, it MAY include an OPTION_LQ_QUERY option along with a query-types defined in [RFC5007] and [RFC5460].
Other DHCPv6 options used in the LEASEQUERY message (as specified in [RFC5460]) can also be used in the ACTIVELEASEQUERY message.
The new message type (STARTTLS) is designed for establishment of a TLS connection between a requestor and a DHCPv6 server. The STARTTLS message SHOULD be sent without any options. Any options received in a STARTTLS message SHOULD be ignored.
More details about this message are specified in Section 8.2.
The LEASEQUERY-REPLY message is defined in [RFC5007]. The LEASEQUERY-DATA and LEASEQUERY-DONE messages are defined in [RFC5460].
In an 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, the DHCPv6 server MUST respond to it with exactly one LEASEQUERY-REPLY message. 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 a LEASEQUERY-DATA message as explained in DHCPv6 Bulk Leasequery [RFC5460]. In case of a query failure, a single LEASEQUERY-REPLY message is returned without any binding data.
New options (OPTION_LQ_BASE_TIME, OPTION_LQ_START_TIME, and OPTION_LQ_END_TIME) are defined as an extension to DHCPv6 Bulk Leasequery [RFC5460]. The reply messages for Active Leasequery use these options along with the options defined in [RFC3315], [RFC5007], and [RFC5460].
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 if the requestor asked for the same in an Active or Bulk Leasequery request. This MUST be an absolute time (i.e., seconds since midnight January 1, 2000 UTC). All of the other time-based options in the reply message are relative to this time, including OPTION_CLT_TIME [RFC5007]. This time is in the context of the DHCPv6 server that placed this option in a message.
This is an unsigned integer in network byte order.
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. This option MAY be used in Active or Bulk Leasequery requests made to a DHCPv6 server.
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 Section 8.5).
Typically (though this is not a requirement), the OPTION_LQ_START_TIME option will contain the value most recently received in an 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 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 a Bulk Leasequery request, but it MUST NOT be used in an 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 Section 8.5).
This is an unsigned integer in network byte order.
Active Leasequery uses the same port configuration as DHCPv6 Bulk Leasequery [RFC5460]. It also uses the other transmission parameters (BULK_LQ_DATA_TIMEOUT and BULK_LQ_MAX_CONNS) as defined in [RFC5460].
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 and to other traffic in the network. As a result, timeout values smaller than the default values SHOULD NOT be used.
While the information communicated by a DHCPv6 Bulk Leasequery [RFC5460] 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 that 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 an OPTION_LQ_START_TIME option (signaling 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 message 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 message 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
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the receive timeout), so that an Active Leasequery requestor would be less likely to miss any changes in the binding.
A requestor attempts to establish a TCP connection to a DHCPv6 server in order to initiate an Active Leasequery exchange. If the attempt fails, the requestor MAY retry. Retries should not be more frequent than one every ACTIVE_LQ_IDLE_TIMEOUT. See Section 6.4.
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. Retries should not be more frequent than one every ACTIVE_LQ_IDLE_TIMEOUT. See Section 6.4.
Messages from the DHCPv6 server come as multiple responses to a single ACTIVELEASEQUERY message. Thus, each ACTIVELEASEQUERY request MUST have a transaction-id unique on the connection on which it is sent, and all of the messages that come as a response to it contain the same transaction-id as the request.
A requestor SHOULD be able to operate in either insecure or secure mode. This MAY be a feature that is administratively controlled.
When operating in insecure mode, the requestor SHOULD proceed to send an ACTIVELEASEQUERY message after the establishment of a TCP connection.
When operating in secure mode, the requestor MUST attempt to negotiate a TLS [RFC5246] connection over the TCP connection. If this negotiation fails, the requestor MUST close the TCP connection. The recommendations in [RFC7525] SHOULD be followed when negotiating this connection.
A requestor requests the establishment of a TLS connection by sending the STARTTLS message to the DHCPv6 server as the first message over the TCP connection. This message indicates to the DHCPv6 server that a TLS connection over this TCP connection is desired. There are four possibilities after the requestor sends the STARTTLS message to the DHCPv6 server:
1. No response from the DHCPv6 server.
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2. The DHCPv6 server closes the TCP connection after it receives the STARTTLS message.
3. The DHCPv6 server responds with a REPLY [RFC3315] message with a DHCPv6 status code of TLSConnectionRefused.
4. The DHCPv6 server responds with a REPLY [RFC3315] message without a DHCPv6 status code, indicating success.
In any of the first three possibilities, the DHCPv6 server can be assumed to not support TLS. In this case, the requestor MUST close the TCP connection.
In the final possibility, where the DHCPv6 server has responded with a REPLY message without a DHCPv6 status code in response to the requestor's STARTTLS message, the requestor SHOULD initiate the exchange of the messages involved in a TLS handshake [RFC5246]. During the TLS handshake, the requestor MUST validate the DHCPv6 server's digital certificate.
If the handshake exchange yields a functioning TLS connection, then the requestor SHOULD transmit an ACTIVELEASEQUERY request over that TLS connection and use that TLS connection for all further interactions in which it engages with the DHCPv6 server over this TCP connection.
If the handshake exchange does not yield a functioning TLS connection, then the requestor MUST close the TCP connection.
Active Leasequery is designed to create a long-lived connection between the requestor and the DHCPv6 server processing the active query. The DHCPv6 server SHOULD send binding information back across this connection with minimal delay after it learns of the binding information. It learns about bindings either because it makes the bindings itself or because it has received information about a binding from another server.
An important capability of 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.
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This capability is enabled by the transmission of an OPTION_LQ_BASE_TIME option with each Leasequery reply sent as the result of a previous Active Leasequery. The requestor SHOULD 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 SHOULD place this highest base-time value into an OPTION_LQ_START_TIME option in the new Active Leasequery request.
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.
If the requestor doesn't wish to request an update of information missed when it was not connected to the DHCPv6 server, then it SHOULD 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 terminate the connection after BULK_LQ_DATA_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.
The requestor attempts to read a DHCPv6 LEASEQUERY-REPLY message from the TCP connection. If the stream of replies becomes blocked, the requestor SHOULD 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 [RFC5007] and DHCPv6 Bulk Leasequery [RFC5460]. If the reply contains a DHCPv6 status code (carried in an OPTION_STATUS_CODE option), the requestor should follow the recommendations in [RFC5007].
Note that the connection resulting from accepting an Active Leasequery request may be long-lived and may not have data transferring continuously during its lifetime. Therefore, the DHCPv6 server SHOULD 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.,
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server has no binding data to send). During a normal exchange of binding data, receiving a LEASEQUERY-DATA message 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 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. If the Active Leasequery was requested with an OPTION_LQ_START_TIME option, the Active Leasequery starts out in the catch-up phase. See Section 8.4.1 for information on processing during the catch-up phase, as well as how to determine when the catch-up phase is complete.
The updates sent by the DHCPv6 server during the catch-up phase are not in the order that the lease state data was updated. Therefore, the OPTION_LQ_BASE_TIME option from messages during this phase MUST NOT be saved and used to compute the subsequent ACTIVELEASEQUERY message's OPTION_LQ_START_TIME option.
After the catch-up phase, or during the entire series of messages received as the response to an 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 that is currently in progress in the event that the DHCPv6 server determines that it cannot continue processing an Active Leasequery 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 the OPTION_LQ_BASE_TIME option in the message. This MUST be the last message on that connection, and once the message has been transmitted, the server MUST close the connection.
After receiving LEASEQUERY-DONE with a QueryTerminated status from a server, the requestor MAY close the TCP connection to that server.
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8.4.1. Processing Replies from a Request Containing an OPTION_LQ_START_TIME
If the Active Leasequery was requested with an OPTION_LQ_START_TIME option, 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 send information about real-time binding updates over the same connection. Thus, the catch-up phase can 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 an OPTION_LQ_START_TIME option. Thus, it is possible that the time specified in the OPTION_LQ_START_TIME option represents a time not covered by the time-ordered information kept by the DHCPv6 server. In such case, when 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 the OPTION_STATUS_CODE option) and LEASEQUERY-DATA messages will begin to 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.
The updates sent by the DHCPv6 server during the catch-up phase are not in the order that the binding data was updated. Therefore, 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 (and used in a subsequent Active Leasequery's query-start-time option), 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 transmits a LEASEQUERY-DATA message with the DHCPv6 status code of CatchUpComplete (or a LEASEQUERY-REPLY message with a
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DHCPv6 status code of DataMissing, as discussed above). 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 Section 8.4, 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 (during transmission, the aging algorithm causes [some of] 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 that 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 can be one or more messages concerning a single binding during the catch-up phase of processing.
Bindings can change multiple times while the requestor is not connected (that is, during the time from the OPTION_LQ_START_TIME to the present). The requestor will only receive information about the current state of the binding, not information about each state change that occurred during the period from the OPTION_LQ_START_TIME to the present.
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 an OPTION_LQ_START_TIME option with the same value as the
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OPTION_LQ_START_TIME option previously included in the Active Leasequery responses from the DHCPv6 server and an OPTION_LQ_END_TIME option equal to the OPTION_LQ_BASE_TIME option returned by the DHCPv6 server in the LEASEQUERY-REPLY or LEASEQUERY-DATA message with the DHCPv6 status code of DataMissing.
Typically, the requestor would have one connection open to a DHCPv6 server for an 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.
8.5. Processing Time Values in Leasequery Messages
Active or Bulk Leasequery requests can 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 an Active or Bulk Leasequery is saving the data returned in some form, it has a requirement to store a variety of time values; 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 an Active or Bulk Leasequery reply message from the DHCPv6 server, the message will contain an 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 options should the requestor need to ever issue an Active or Bulk Leasequery message using these options as part of a later query, since these options require a time in the context of the DHCPv6 server.
In addition to saving the OPTION_LQ_BASE_TIME for possible future use in the OPTION_LQ_START_TIME or OPTION_LQ_END_TIME options, the OPTION_LQ_BASE_TIME option is used as part of the conversion of the other times in the Leasequery message to values that are meaningful in the context of the requestor.
In systems whose clocks are synchronized, perhaps using the Network Time Protocol (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 is no requirement that these sequences must be followed.
This example illustrates the message flows in case the DHCPv6 server identifies that it cannot accept and/or process an Active Leasequery request from the requestor. This could be because of various reasons (i.e., UnknownQueryType, MalformedQuery, NotConfigured, NotAllowed, and NotSupported).
This example illustrates the message flows in case the 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.
This example illustrates the message flows in case of successful query processing by the 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
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LEASEQUERY-DATA messages. In case the DHCPv6 server wants to abort an in-process request and terminate the connection due to some reason, it sends LEASEQUERY-DONE with an error code present in the OPTION_STATUS_CODE option.
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 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.
DHCPv6 servers that implement DHCPv6 Active Leasequery listen for incoming TCP connections. The approach used in accepting the requestor's connection is the same as specified in DHCPv6 Bulk Leasequery [RFC5460], with the exception that support for Active Leasequery MUST NOT be enabled by default and MUST require an explicit configuration step to be performed before it will operate.
DHCPv6 servers SHOULD be able to operate in either insecure or secure mode. This MAY be a mode that is administratively controlled, where the server will require a TLS connection to operate or will only operate without a TLS connection. In either case, operation in insecure mode MUST NOT be the default, even if operation in secure mode is not supported. Operation in insecure mode MUST always require an explicit configuration step, separate from the configuration step required to enable support for Active Leasequery.
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When operating in insecure mode, the DHCPv6 server simply waits for the requestor to send the Active Leasequery request after the establishment of a TCP connection. If it receives a STARTTLS message, it MUST respond with a REPLY [RFC3315] message with a DHCPv6 status code of TLSConnectionRefused.
When operating in secure mode, DHCPv6 servers MUST support TLS [RFC5246] to protect the integrity and privacy of the data transmitted over the TCP connection. When operating in secure mode, DHCPv6 servers MUST be configurable with regard to which requestors they will communicate. The certificate presented by a requestor when initiating the TLS connection is used to distinguish between acceptable and unacceptable requestors.
When operating in secure mode, the DHCPv6 server MUST begin to negotiate a TLS connection with a requestor who asks for one and MUST close the TCP connections that are not secured with TLS or for which the requestor's certificate is deemed unacceptable. The recommendations in [RFC7525] SHOULD be followed when negotiating a TLS connection.
A requestor will request a TLS connection by sending a STARTTLS as the first message over a newly created TCP connection. If the DHCPv6 server supports TLS connections and has not been configured to not allow them on this link, the DHCPv6 server MUST respond to this STARTTLS message by sending a REPLY [RFC3315] message without a DHCPv6 status code back to the requestor. This indicates to the requestor that the DHCPv6 server will support the negotiation of a TLS connection over this existing TCP connection.
If for some reason the DHCPv6 server cannot support a TLS connection or has been configured to not support a TLS connection, then it SHOULD send a REPLY message with a DHCPv6 status code of TLSConnectionRefused back to the requestor.
In the event that the DHCPv6 server sends a REPLY message without a DHCPv6 status code option included (which indicates success), the requestor is supposed to initiate a TLS handshake [RFC5246] (see Section 8.2). During the TLS handshake, the DHCPv6 server MUST validate the requestor's digital certificate. In addition, the digital certificate presented by the requestor is used to decide if this requestor is allowed to perform an Active Leasequery. If this requestor's certificate is deemed unacceptable, the server MUST abort the creation of the TLS connection.
All TLS connections established between a requestor and a DHCPv6 server for the purposes of supporting Active Leasequery MUST be mutually authenticated.
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If the TLS handshake is not successful in creating a TLS connection, the server MUST close the TCP connection.
Servers that do not implement DHCPv6 Active and Bulk Leasequery SHOULD NOT listen for incoming TCP connections for these requests.
If the DHCPv6 server supporting Bulk Leasequery and not Active Leasequery receives an Active Leasequery request, it SHOULD send a LEASEQUERY-REPLY with a DHCPv6 status code of NotSupported. It SHOULD close the TCP connection after this error is signaled.
The DHCPv6 Leasequery [RFC5007] 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 [RFC5460]. Message transmission and framing for TCP is described in Section 6.1.
If the connection becomes blocked while the server is attempting to send reply messages, the server SHOULD terminate the TCP connection after ACTIVE_LQ_SEND_TIMEOUT. This timeout governs for how long the DHCPv6 server is prepared to wait for the requestor to read and process enough information to unblock the TCP 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 SHOULD close the TCP connection.
If the DHCPv6 server encounters an error during the 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 signaled.
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 signaled.
If the server finds any bindings satisfying a query, it SHOULD send 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 [RFC5007]. The server SHOULD send subsequent bindings in LEASEQUERY-DATA messages, which can avoid redundant data (such as the requestor's Client-ID).
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Every reply to an Active Leasequery request MUST contain the information specified in replies to a DHCPv6 Bulk Leasequery request [RFC5460], with the exception that a server implementing Active Leasequery SHOULD be able to be configured to prevent specific data items from being sent to the requestor even if these data items were requested in the OPTION_ORO option.
Some servers can be configured to respond to a DHCPv6 Leasequery [RFC5007] and DHCPv6 Bulk Leasequery [RFC5460] for an IPv6 binding that is reserved in such a way that it appears that the IPv6 binding is leased to the DHCP client for which it is reserved. These servers SHOULD also respond to an Active Leasequery request with the same information as they would to a Bulk Leasequery request when they first determine that the IPv6 binding is reserved to a DHCP client.
If an Active Leasequery or Bulk Leasequery request contains the OPTION_LQ_BASE_TIME option code present in OPTION_ORO, the DHCPv6 server MUST include the OPTION_LQ_BASE_TIME option in every reply for this request. The value for the base-time option is the current absolute time in the DHCPv6 server's context.
If an Active Leasequery request contains an 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 the OPTION_LQ_END_TIME option appears in an 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 an 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.
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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 that would be wasted if there are no Active Leasequery requestors 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 requestor or the server closes the connection.
Every Active Leasequery request MUST be made on a single TCP connection where there is no other request active at the time the request is made.
Typically, a requestor of an 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 in parallel would be possible and reasonable. In case of parallel Active and Bulk Leasequeries, the requestor MUST use different TCP connections.
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.
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
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status code in the DHCPv6 status code option in a LEASEQUERY-DONE message. If the server detects that the requestor end has been closed, the server MUST close its end of the connection.
The server SHOULD limit the number of connections it maintains and SHOULD close idle connections to enforce the limit.
The Security Considerations section of [RFC3315] details the general threats to DHCPv6. The DHCPv6 Leasequery specification [RFC5007] 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 requestors, and use of IPsec [RFC4301].
The use of TCP introduces some additional concerns. Attacks that attempt to exhaust the DHCPv6 server's available TCP connection resources 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 can also exhaust a server's pool of available connections.
When operating in secure mode, TLS [RFC5246] is used to secure the connection. The recommendations in [RFC7525] SHOULD be followed when negotiating a TLS connection.
Servers SHOULD offer configuration parameters to limit the sources of incoming connections through validation and use of the digital certificates presented to create a TLS connection. They SHOULD also limit the number of accepted connections and limit the period of time during which an idle connection will be left open.
The data acquired by using an Active Leasequery is subject to the same potential abuse as the data held by the DHCPv6 server from which it was acquired and SHOULD be secured by mechanisms as strong as those used for the data held by that DHCPv6 server. The data acquired by using an Active Leasequery SHOULD be deleted as soon as possible after the use for which it was acquired has passed.
Authentication for DHCP messages [RFC3315] MUST NOT be used to attempt to secure transmission of the messages described in this document.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, "Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May 2015, <http://www.rfc-editor.org/info/rfc7525>.
Some of the concepts and content present in this document are based on DHCPv4 Active Leasequery, which was originally proposed by Kim Kinnear, Bernie Volz, Mark Stapp, and Neil Russell.
Useful review comments were provided by Scott Bradner, Francis Dupont, and Stephen Farrell. The privacy protections were substantially upgraded due to these comments and discussions.
Authors' Addresses
Dushyant Raghuvanshi Cisco Systems, Inc. Cessna Business Park Varthur Hobli, Outer Ring Road Bangalore, Karnataka 560037 India
Phone: +91 80 4426-7372 Email: draghuva@cisco.com
Kim Kinnear Cisco Systems, Inc. 1414 Massachusetts Avenue Boxborough, Massachusetts 01719 United States
Phone: +1 978 936-0000 Email: kkinnear@cisco.com
Deepak Kukrety Cisco Systems, Inc. Cessna Business Park Varthur Hobli, Outer Ring Road Bangalore, Karnataka 560037 India