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RFC 7513

 
 
 

Source Address Validation Improvement (SAVI) Solution for DHCP

Part 2 of 3, p. 17 to 45
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5.  Binding State Table (BST)

   The Binding State Table, which may be implemented centrally in the
   switch or distributed among its ports, is used to contain the
   bindings between the IP addresses assigned to the attachments and the
   corresponding binding anchors of the attachments.  Note that in this
   description, there is a binding entry for each IPv4 or IPv6 address
   associated with each binding anchor, and there may be several of each
   such address, especially if the port is extended using a protected
   non-SAVI device.  Each binding entry has six fields:

   o  Binding Anchor (listed as "Anchor" in subsequent figures): the
      binding anchor, i.e., one or more physical and/or link-layer
      properties of the attachment.

   o  IP Address (listed as "Address" in subsequent figures): the IPv4
      or IPv6 address assigned to the attachment by DHCP.

   o  State: the state of the binding.  Possible values of this field
      are listed in Sections 6.2 and 7.3.

   o  Lifetime: the remaining seconds of the binding.  Internally, this
      MAY be stored as the timestamp value at which the lifetime
      expires.

   o  Transaction ID (TID): the Transaction ID [RFC2131] [RFC3315] of
      the corresponding DHCP transaction.  The TID field is used to

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      associate DHCP Server-to-Client messages with corresponding
      binding entries.

   o  Timeouts: the number of timeouts that expired in the current state
      (only used in the Data Snooping Process; see Section 7).

   The IA is not present in the BST for three reasons:

   o  The lease of each address in one IA is assigned separately.

   o  When the binding is set up based on data snooping, the IA cannot
      be recovered from the leasequery protocol.

   o  DHCPv4 does not define an IA.

   An example of such a table is shown in Figure 4.

    +---------+----------+-----------+-----------+--------+----------+
    | Anchor  | Address  | State     | Lifetime  | TID    | Timeouts |
    +---------+----------+-----------+-----------+--------+----------+
    | Port_1  | IP_1     | BOUND     |  65535    | TID_1  |     0    |
    +---------+----------+-----------+-----------+--------+----------+
    | Port_1  | IP_2     | BOUND     |  10000    | TID_2  |     0    |
    +---------+----------+-----------+-----------+--------+----------+
    | Port_2  | IP_3     | INIT_BIND |      1    | TID_3  |     0    |
    +---------+----------+-----------+-----------+--------+----------+

                   Figure 4: Example Binding State Table

6.  DHCP Snooping Process

   This section specifies the process of setting up bindings based on
   DHCP snooping.  This process is illustrated using a state machine.

6.1.  Rationale

   The rationale of the DHCP Snooping Process is that if a DHCP client
   is legitimately using a DHCP-assigned address, the DHCP address
   assignment procedure that assigns the IP address to the client must
   have been performed via the client's point of attachment.  This
   assumption works when the SAVI device is always on the path(s) from
   the DHCP client to the DHCP server(s)/relay(s).  Without considering
   the movement of DHCP clients, the SAVI device should be the cut
   vertex whose removal will separate the DHCP client and the remaining
   network containing the DHCP server(s)/relay(s).  For most of the
   networks whose topologies are simple, it is possible to deploy this
   SAVI function at proper devices to meet this requirement.

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   However, if there are multiple paths from a DHCP client to the DHCP
   server and the SAVI device is only on one of them, there is an
   obvious failure case: the SAVI device may not be able to snoop the
   DHCP procedure.  Host movement may also make this requirement
   difficult to meet.  For example, when a DHCP client moves from one
   attachment to another attachment in the same network, it may fail to
   reinitialize its interface or send a Confirm message because of
   incomplete protocol implementation.  Thus, there can be scenarios in
   which only performing this DHCP Snooping Process is insufficient to
   set up bindings for all the valid DHCP addresses.  These exceptions
   and the solutions are discussed in Section 7.

6.2.  Binding States Description

   The following binding states are present in this process and the
   corresponding state machine:

   NO_BIND: No binding has been set up.

   INIT_BIND: A potential binding has been set up.

   BOUND: The binding has been set up.

6.3.  Events

   This section describes events in this process and the corresponding
   state machine transitions.  The DHCP message categories (e.g., DHCPv4
   Discover) defined in Section 3 are used extensively in the
   definitions of events and elsewhere in the state machine definition.
   If an event will trigger the creation of a new binding entry, the
   binding entry limit on the binding anchor MUST NOT be exceeded.

6.3.1.  Timer Expiration Event

   EVE_ENTRY_EXPIRE: The lifetime of a binding entry expires.

6.3.2.  Control Message Arriving Events

   EVE_DHCP_REQUEST: A DHCPv4 Request or a DHCPv6 Request message is
   received.

   EVE_DHCP_CONFIRM: A DHCPv6 Confirm message is received.

   EVE_DHCP_REBOOT: A DHCPv4 Reboot message is received.

   EVE_DHCP_REBIND: A DHCPv4 Rebind or a DHCPv6 Rebind message is
   received.

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   EVE_DHCP_RENEW: A DHCPv4 Renew or a DHCPv6 Renew message is received.

   EVE_DHCP_SOLICIT_RC: A DHCPv6 Solicitation message with the Rapid
   Commit option is received.

   EVE_DHCP_REPLY: A DHCPv4 ACK or a DHCPv6 Reply message is received.

   EVE_DHCP_DECLINE: A DHCPv4 Decline or a DHCPv6 Decline message is
   received.

   EVE_DHCP_RELEASE: A DHCPv4 Release or a DHCPv6 Release message is
   received.

   EVE_DHCP_LEASEQUERY: A successful DHCPv6 LEASEQUERY-REPLY (refer to
   Section 4.3.3 of [RFC5007]) is received.

   Note: the events listed here do not cover all the DHCP messages in
   Section 3.  The messages that do not really determine address usage
   (DHCPv4 Discover, DHCPv4 Inform, DHCPv6 Solicit without Rapid Commit,
   DHCPv6 Information-Request, DHCPv4 Offer, DHCPv6 Advertise, and
   DHCPv6 Reconfigure) and that are not necessary to snoop (DHCPv4
   Negative Acknowledgment (NAK); refer to Section 6.4.2.3) are not
   included.  Note also that DHCPv4 DHCPLEASEQUERY is not used in the
   DHCP Snooping Process to avoid confusion with Section 7.  Also, since
   the LEASEQUERY should have been originated by the SAVI device itself,
   the destination check should verify that the message is directed to
   this SAVI device, and it should not be forwarded once it has been
   processed here.

   Moreover, only if a DHCP message can pass the following checks, the
   corresponding event is regarded as a valid event:

   o  Attribute check: the DHCP Server-to-Client messages and
      LEASEQUERY-REPLY should be from attachments with the DHCP-Trust
      attribute; the DHCP Client-to-Server messages should be from
      attachments with the DHCP-Snooping attribute.

   o  Destination check: the DHCP Server-to-Client messages should be
      destined to attachments with the DHCP-Snooping attribute.  This
      check is performed to ensure the binding is set up on the SAVI
      device that is nearest to the destination client.

   o  Binding anchor check: the DHCP Client-to-Server messages that may
      trigger modification or removal of an existing binding entry must
      have a matching binding anchor with the corresponding entry.

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   o  TID check: the DHCP Server-to-Client/Client-to-Server messages
      that may cause modification of existing binding entries must have
      a matched TID with the corresponding entry.  Note that this check
      is not performed on LEASEQUERY and LEASEQUERY-REPLY messages as
      they are exchanged between the SAVI devices and the DHCP servers.
      Besides, this check is not performed on DHCP Renew/Rebind
      messages.

   o  Binding limitation check: the DHCP messages must not cause new
      binding setup on an attachment whose binding entry limitation has
      been reached (refer to Section 11.5).

   o  Address check: the source address of the DHCP messages should pass
      the check specified in Section 8.2.

   On receiving a DHCP message without triggering a valid event, the
   state will not change, and the actions will not be performed.  Note
   that if a message does not trigger a valid event but it can pass the
   checks in Section 8.2, it MUST be forwarded.

6.4.  The State Machine of DHCP Snooping Process

   This section specifies state transitions and their corresponding
   actions.

6.4.1.  Initial State: NO_BIND

6.4.1.1.  Event: EVE_DHCP_REQUEST - A DHCPv4 Request or a DHCPv6 Request
          message is received

   The SAVI device MUST forward the message.

   The SAVI device will generate an entry in the BST.  The Binding
   Anchor field is set to the binding anchor of the attachment from
   which the message is received.  The State field is set to INIT_BIND.
   The Lifetime field is set to be MAX_DHCP_RESPONSE_TIME.  The TID
   field is set to the TID of the message.  If the message is DHCPv4
   Request, the Address field can be set to the address to request,
   i.e., the 'requested IP address'.  An example of the entry is
   illustrated in Figure 5.

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   +--------+-------+---------+-----------------------+-----+----------+
   | Anchor |Address| State   | Lifetime              | TID | Timeouts |
   +--------+-------+---------+-----------------------+-----+----------+
   | Port_1 |       |INIT_BIND|MAX_DHCP_RESPONSE_TIME | TID |     0    |
   +--------+-------+---------+-----------------------+-----+----------+

       Figure 5: Binding Entry in BST on Initialization Triggered by
                   Request/Rapid Commit/Reboot Messages

   Resulting state: INIT_BIND - A potential binding has been set up.

6.4.1.2.  Event: EVE_DHCP_REBOOT - A DHCPv4 Reboot message is received

   The SAVI device MUST forward the message.

   The SAVI device will generate an entry in the BST.  The Binding
   Anchor field is set to the binding anchor of the attachment from
   which the message is received.  The State field is set to INIT_BIND.
   The Lifetime field is set to be MAX_DHCP_RESPONSE_TIME.  The TID
   field is set to the TID of the message.  If the message is DHCPv4
   Reboot, the Address field can be set to the address to request, i.e.,
   the 'requested IP address'.  An example of the entry is illustrated
   in Figure 5.

   Resulting state: INIT_BIND - A potential binding has been set up.

6.4.1.3.  Event: EVE_DHCP_SOLICIT_RC - A DHCPv6 Solicitation message
          with the Rapid Commit option is received

   The SAVI device MUST forward the message.

   The SAVI device will generate an entry in the BST.  The Binding
   Anchor field is set to the binding anchor of the attachment from
   which the message is received.  The State field is set to INIT_BIND.
   The Lifetime field is set to be MAX_DHCP_RESPONSE_TIME.  The TID
   field is set to the TID of the message.  An example of the entry is
   illustrated in Figure 5.

   Resulting state: INIT_BIND - A potential binding has been set up.

6.4.1.4.  Event: EVE_DHCP_CONFIRM - A DHCPv6 Confirm message is received

   The SAVI device MUST forward the message.

   The SAVI device will generate corresponding entries in the BST for
   each address in each Identity Association (IA) option of the Confirm
   message.  The Binding Anchor field is set to the binding anchor of
   the attachment from which the message is received.  The State field

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   is set to INIT_BIND.  The Lifetime field is set to be
   MAX_DHCP_RESPONSE_TIME.  The TID field is set to the TID of the
   message.  The Address field is set to the address(es) to confirm.  An
   example of the entries is illustrated in Figure 6.

   +--------+-------+---------+-----------------------+-----+----------+
   | Anchor |Address| State   | Lifetime              | TID | Timeouts |
   +--------+-------+---------+-----------------------+-----+----------+
   | Port_1 | Addr1 |INIT_BIND|MAX_DHCP_RESPONSE_TIME | TID |    0     |
   +--------+-------+---------+-----------------------+-----+----------+
   | Port_1 | Addr2 |INIT_BIND|MAX_DHCP_RESPONSE_TIME | TID |    0     |
   +--------+-------+---------+-----------------------+-----+----------+

    Figure 6: Binding Entry in BST on Confirm-Triggered Initialization

   Resulting state: INIT_BIND - A potential binding has been set up.

6.4.1.5.  Events That Cannot Happen in the NO_BIND State

   o  EVE_ENTRY_EXPIRE: The lifetime of a binding entry expires

   o  EVE_DHCP_REBIND: A DHCPv4 Rebind or a DHCPv6 Rebind message is
      received

   o  EVE_DHCP_RENEW: A DHCPv4 Renew or a DHCPv6 Renew message is
      received

   o  EVE_DHCP_REPLY: A DHCPv4 ACK or a DHCPv6 Reply message is received

   o  EVE_DHCP_DECLINE: A DHCPv4 Decline or a DHCPv6 Decline message is
      received

   o  EVE_DHCP_RELEASE: A DHCPv4 Release or a DHCPv6 Release message is
      received

   o  EVE_DHCP_LEASEQUERY: A successful DHCPv6 LEASEQUERY-REPLY is
      received

   These cannot happen because they are each something that happens
   AFTER a binding has been created.

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6.4.2.  Initial State: INIT_BIND

6.4.2.1.  Event: EVE_DHCP_REPLY - A DHCPv4 ACK or a DHCPv6 Reply message
          is received

   The message MUST be forwarded to the corresponding client.

   If the message is DHCPv4 ACK, the Address field of the corresponding
   entry (i.e., the binding entry whose TID is the same as the message)
   is set to the address in the message (i.e., 'yiaddr' in DHCPv4 ACK).
   The Lifetime field is set to the sum of the lease time in the ACK
   message and MAX_DHCP_RESPONSE_TIME.  The State field is changed to
   BOUND.

   If the message is DHCPv6 Reply, note the following cases:

   1.  If the status code is not "Success", no modification of
       corresponding entries will be made.  Corresponding entries will
       expire automatically if no "Success" Reply is received during the
       lifetime.  The entries are not removed immediately because the
       client may be able to use the addresses whenever a "Success"
       Reply is received ("If the client receives any Reply messages
       that do not indicate a NotOnLink status, the client can use the
       addresses in the IA and ignore any messages that indicate a
       NotOnLink status" [RFC3315]).

   2.  If the status code is "Success", the SAVI device checks the IA
       options in the Reply message.

       A.  If there are IA options in the Reply message, the SAVI device
           checks each IA option.  When the first assigned address is
           found, the Address field of the binding entry with a matched
           TID is set to the address.  The Lifetime field is set to the
           sum of the lease time in the Reply message and
           MAX_DHCP_RESPONSE_TIME.  The State field is changed to BOUND.
           If there is more than one address assigned in the message,
           new binding entries are set up for the remaining address
           assigned in the IA options.  An example of the entries is
           illustrated in Figure 8.  SAVI devices do not specially
           process IA options with a NoAddrsAvail status because there
           should be no address contained in such IA options.

       B.  Otherwise, the DHCP Reply message is in response to a Confirm
           message.  The state of the binding entries with a matched TID
           is changed to BOUND.  Because [RFC3315] does not require the
           lease time of addresses to be contained in the Reply message,
           the SAVI device SHOULD send a LEASEQUERY [RFC5007] message
           querying by IP address to the All_DHCP_Servers multicast

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           address [RFC3315] or a list of configured DHCP server
           addresses.  The LEASEQUERY message is generated for each IP
           address if multiple addresses are confirmed.  The lifetime of
           corresponding entries is set to 2*MAX_LEASEQUERY_DELAY.  If
           there is no response message after MAX_LEASEQUERY_DELAY, send
           the LEASEQUERY message again.  An example of the entries is
           illustrated in Figure 7.  If the SAVI device does not send
           the LEASEQUERY message, a preconfigured lifetime
           DHCP_DEFAULT_LEASE MUST be set on the corresponding entry.
           (Note: it is RECOMMENDED to use T1 configured on DHCP servers
           as the DHCP_DEFAULT_LEASE.)

   Note: the SAVI devices do not check if the assigned addresses are
   duplicated because in SAVI-DHCP scenarios, the DHCP servers are the
   only source of valid addresses.  However, the DHCP servers should be
   configured to make sure no duplicated addresses are assigned.

   +--------+-------+-------+------------------------+-----+----------+
   | Anchor |Address| State | Lifetime               | TID | Timeouts |
   +--------+-------+-------+------------------------+-----+----------+
   | Port_1 | Addr1 | BOUND | 2*MAX_LEASEQUERY_DELAY | TID |    0     |
   +--------+-------+-------+------------------------+-----+----------+
   | Port_1 | Addr2 | BOUND | 2*MAX_LEASEQUERY_DELAY | TID |    0     |
   +--------+-------+-------+------------------------+-----+----------+

      Figure 7: From INIT_BIND to BOUND on DHCP Reply in Response to
                                  Confirm

   Transition
   +--------+-------+-------+------------------------+-----+----------+
   | Anchor |Address| State | Lifetime               | TID | Timeouts |
   +--------+-------+-------+------------------------+-----+----------+
   | Port_1 | Addr1 | BOUND |Lease time+             | TID |    0     |
   |        |       |       |MAX_DHCP_RESPONSE_TIME  |     |          |
   +--------+-------+-------+------------------------+-----+----------+
   | Port_1 | Addr2 | BOUND |Lease time+             | TID |    0     |
   |        |       |       |MAX_DHCP_RESPONSE_TIME  |     |          |
   +--------+-------+-------+------------------------+-----+----------+

      Figure 8: From INIT_BIND to BOUND on DHCP Reply in Response to
                                  Request

   Resulting state: BOUND - The binding has been set up.

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6.4.2.2.  Event: EVE_ENTRY_EXPIRE - The lifetime of a binding entry
          expires

   The entry MUST be deleted from the BST.

   Resulting state: An entry that has been deleted from the BST may be
   considered to be in the "NO_BIND" state - No binding has been set up.

6.4.2.3.  Events That Are Ignored in INIT_BIND

   If no DHCP Server-to-Client messages that assign addresses or confirm
   addresses are received, corresponding entries will expire
   automatically.  Thus, other DHCP Server-to-Client messages (e.g.,
   DHCPv4 NAK) are not specially processed.

   As a result, the following events, should they occur, are ignored
   until either a DHCPv4 ACK or a DHCPv6 Reply message is received or
   the lifetime of the binding entry expires.

   o  EVE_DHCP_REQUEST: A DHCPv4 Request or a DHCPv6 Request message is
      received

   o  EVE_DHCP_CONFIRM: A DHCPv6 Confirm message is received

   o  EVE_DHCP_REBOOT: A DHCPv4 Reboot message is received

   o  EVE_DHCP_REBIND: A DHCPv4 Rebind or a DHCPv6 Rebind message is
      received

   o  EVE_DHCP_RENEW: A DHCPv4 Renew or a DHCPv6 Renew message is
      received

   o  EVE_DHCP_SOLICIT_RC: A DHCPv6 Solicitation message with the Rapid
      Commit option is received

   o  EVE_DHCP_DECLINE: A DHCPv4 Decline or a DHCPv6 Decline message is
      received

   o  EVE_DHCP_RELEASE: A DHCPv4 Release or a DHCPv6 Release message is
      received

   o  EVE_DHCP_LEASEQUERY: A successful DHCPv6 LEASEQUERY-REPLY is
      received

   In each case, the message MUST be forwarded.

   Resulting state: INIT_BIND - A potential binding has been set up.

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6.4.3.  Initial State: BOUND

6.4.3.1.  Event: EVE_ENTRY_EXPIRE - The lifetime of a binding entry
          expires

   The entry MUST be deleted from the BST.

   Resulting state: An entry that has been deleted from the BST may be
   considered to be in the "NO_BIND" state - No binding has been set up.

6.4.3.2.  Event: EVE_DHCP_DECLINE - A DHCPv4 Decline or a DHCPv6 Decline
          message is received

   The message MUST be forwarded.

   First, the SAVI device gets all the addresses ("Requested IP address"
   in DHCPv4 Decline, "ciaddr" in DHCPv4 Release, and addresses in all
   the IA options of DHCPv6 Decline/Release) to decline/release in the
   message.  Then, the corresponding entries MUST be removed.

   Resulting state in each relevant BST entry: An entry that has been
   deleted from the BST may be considered to be in the "NO_BIND" state -
   No binding has been set up.

6.4.3.3.  Event: EVE_DHCP_RELEASE - A DHCPv4 Release or a DHCPv6 Release
          message is received

   The message MUST be forwarded.

   First, the SAVI device gets all the addresses ("Requested IP address"
   in DHCPv4 Decline, "ciaddr" in DHCPv4 Release, and addresses in all
   the IA options of DHCPv6 Decline/Release) to decline/release in the
   message.  Then, the corresponding entries MUST be removed.

   Resulting state in each relevant BST entry: An entry that has been
   deleted from the BST may be considered to be in the "NO_BIND" state -
   No binding has been set up.

6.4.3.4.  Event: EVE_DHCP_REBIND - A DHCPv4 Rebind or a DHCPv6 Rebind
          message is received

   The message MUST be forwarded.

   In such a case, a new TID will be used by the client.  The TID field
   of the corresponding entries MUST be set to the new TID.  Note that
   the TID check will not be performed on such messages.

   Resulting state: BOUND: The binding has been set up.

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6.4.3.5.  Event: EVE_DHCP_RENEW - A DHCPv4 Renew or a DHCPv6 Renew
          message is received

   The message MUST be forwarded.

   In such a case, a new TID will be used by the client.  The TID field
   of the corresponding entries MUST be set to the new TID.  Note that
   the TID check will not be performed on such messages.

   Resulting state: BOUND: The binding has been set up.

6.4.3.6.  Event: EVE_DHCP_REPLY - A DHCPv4 ACK or a DHCPv6 Reply message
          is received

   The message MUST be forwarded.

   The DHCP Reply messages received in current states should be in
   response to DHCP Renew/Rebind.

   If the message is DHCPv4 ACK, the SAVI device updates the binding
   entry with a matched TID, with the Lifetime field set to be the sum
   of the new lease time and MAX_DHCP_RESPONSE_TIME, leaving the entry
   in the BOUND state.

   If the message is DHCPv6 Reply, the SAVI device checks each IA
   Address option in each IA option.  For each:

   1.  If the IA entry in the REPLY message has the status "NoBinding",
       there is no address in the option, and no operation on an address
       is performed.

   2.  If the valid lifetime of an IA Address option is 0, the binding
       entry with a matched TID and address is removed, leaving it
       effectively in the NO_BIND state.

   3.  Otherwise, set the Lifetime field of the binding entry with the
       matched TID and address to be the sum of the new valid lifetime
       and MAX_DHCP_RESPONSE_TIME, leaving the entry in the BOUND state.

   Resulting state: NO_BIND or BOUND, as specified.

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6.4.3.7.  Event: EVE_DHCP_LEASEQUERY - A successful DHCPv6
          LEASEQUERY_REPLY is received

   The message MUST be forwarded.

   The message should be in response to the LEASEQUERY message sent in
   Section 6.4.2.  The related binding entry can be determined based on
   the address in the IA Address option in the LEASEQUERY-REPLY message.
   The Lifetime field of the corresponding binding entry is set to the
   sum of the lease time in the LEASEQUERY-REPLY message and
   MAX_DHCP_RESPONSE_TIME.

   Resulting state: BOUND: The binding has been set up.

6.4.3.8.  Events Not Processed in the State BOUND

   The following events are ignored if received while the indicated
   entry is in the BOUND state.  Any required action will be the result
   of the next message in the client/server exchange.

   o  EVE_DHCP_REQUEST: A DHCPv4 Request or a DHCPv6 Request message is
      received

   o  EVE_DHCP_CONFIRM: A DHCPv6 Confirm message is received

   o  EVE_DHCP_REBOOT: A DHCPv4 Reboot message is received

   o  EVE_DHCP_SOLICIT_RC: A DHCPv6 Solicitation message with the Rapid
      Commit option is received

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6.4.4.  Table of State Machine

   The main state transits are listed as follows.  Note that not all the
   details are specified in the table and the diagram.

   State       Event             Action                       Next State
   ---------------------------------------------------------------------
   NO_BIND     RQ/RC/CF/RE       Generate entry                INIT_BIND

   INIT_BIND   RPL               Record lease time                 BOUND
                                 (send leasequery if no lease)

   INIT_BIND   EVE_ENTRY_EXPIRE  Remove entry                    NO_BIND

   BOUND       RLS/DCL           Remove entry                    NO_BIND

   BOUND       EVE_ENTRY_EXPIRE  Remove entry                    NO_BIND

   BOUND       RPL               Set new lifetime                  BOUND

   BOUND       LQR               Record lease time                 BOUND

                     Figure 9: State Transition Table

   RQ:  EVE_DHCP_REQUEST
   RC:  EVE_DHCP_SOLICIT_RC
   CF:  EVE_DHCP_CONFIRM
   RE:  EVE_DHCP_REBOOT
   RPL: EVE_DHCP_REPLY
   RLS: EVE_DHCP_RELEASE
   DCL: EVE_DHCP_DECLINE
   LQR: EVE_DHCP_LEASEQUERY

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                               +-------------+
                               |             |
                      /--------+   NO_BIND   |<--------\
                      |  ----->|             |         |
                      |  |     +-------------+         |EVE_DHCP_RELEASE
   EVE_DHCP_REQUEST   |  |                             |EVE_DHCP_DECLINE
   EVE_DHCP_CONFIRM   |  |EVE_ENTRY_EXPIRE             |EVE_ENTRY_EXPIRE
   EVE_DHCP_SOLICIT_RC|  |                             |
   EVE_DHCP_REBOOT    |  |                             |
                      |  |                             |
                      |  |                             |
                      v  |                             |
              +-------------+                      +------------+
              |             |    EVE_DHCP_REPLY   |            |
              |  INIT_BIND  --------------------->|    BOUND   |<-\
              |             |                     |            |  |
              +-------------+                     +------------+  |
                                                         |        |
                                                         \--------/
                                               EVE_DHCP_REPLY
                                               EVE_DHCP_LEASEQUERY

                       Figure 10: Diagram of Transit

7.  Data Snooping Process

7.1.  Scenario

   The rationale of the DHCP Snooping Process specified in Section 6 is
   that if a DHCP client's use of a DHCP address is legitimate, the
   corresponding DHCP address assignment procedure must have been
   finished during the attachment of the DHCP client.  This is the case
   when the SAVI device is continuously on the path(s) from the DHCP
   client to the DHCP server(s)/relay(s).  However, there are two cases
   in which this does not work:

   o  Multiple paths: there is more than one feasible link-layer path
      from the client to the DHCP server/relay, and the SAVI device is
      not on every one of them.  The client may get its address through
      one of the paths that does not pass through the SAVI device, but
      packets from the client can travel on paths that pass through the
      SAVI device, such as when the path through the link-layer network
      changes.  Because the SAVI device could not snoop the DHCP packet
      exchange procedure, the DHCP Snooping Process cannot set up the
      corresponding binding.

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   o  Dynamic path: there is only one feasible link-layer path from the
      client to the DHCP server/relay, but the path is dynamic due to
      topology change (for example, some link becomes broken due to
      failure or some planned change) or link-layer path change.  This
      situation also covers the local-link movement of clients without
      the address confirm/reconfiguration process.  For example, a host
      changes its attached switch port in a very short time.  In such
      cases, the DHCP Snooping Process will not set up the corresponding
      binding.

   The Data Snooping Process can avoid the permanent blocking of
   legitimate traffic in case one of these two exceptions occurs.  This
   process is performed on attachments with the Data-Snooping attribute.
   Data packets without a matching binding entry may trigger this
   process to set up bindings.

   Snooping data traffic introduces a considerable burden on the
   processor and ASIC-to-Processor bandwidth of SAVI devices.  Because
   of the overhead of this process, the implementation of this process
   is OPTIONAL.  This function SHOULD be enabled unless the
   implementation is known to be used in the scenarios without the above
   exceptions.  For example, if the implementation is to be used in
   networks with tree topology and without host local-link movement,
   there is no need to implement this process in such scenarios.

   This process is not intended to set up a binding whenever a data
   packet without a matched binding entry is received.  Instead,
   unmatched data packets trigger this process probabilistically, and
   generally a number of unmatched packets will be discarded before the
   binding is set up.  The parameter(s) of this probabilistic process
   SHOULD be configurable, defaulting to a situation where data snooping
   is disabled.

7.2.  Rationale

   This process makes use of NS/ARP and DHCP Leasequery to set up
   bindings.  If an address is not used by another client in the
   network, and the address has been assigned in the network, the
   address can be bound with the binding anchor of the attachment from
   which the unmatched packet is received.

   The Data Snooping Process provides an alternative path for binding
   entries to reach the BOUND state in the exceptional cases explained
   in Section 7.1 when there are no DHCP messages that can be snooped by
   the SAVI device.

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   In some of the exceptional cases (especially the dynamic topology
   case), by the time the binding has reached the BOUND state, the DHCP
   messages may be passing through the SAVI device.  In this case, the
   events driven by DHCP messages that are expected in the BOUND state
   in the DHCP Snooping Process may occur, and the binding can be
   handled by the DHCP Snooping Process state machine.

   In any event, the lease expiry timeout event will occur even if no
   others do.  This will cause the binding to be deleted and the state
   to logically return to NO_BIND state.  Either the DHCP or the Data
   Snooping Process will be reinvoked if the lease is still in place.
   If DHCP messages are still not passing through the SAVI device, there
   will be a brief disconnection during which data packets passing
   through the SAVI device will be dropped.  The probabilistic
   initiation of the Data Snooping Process can then take over again and
   return the binding state to BOUND in due course.

   The security issues concerning this process are discussed in
   Section 11.1.

7.3.  Additional Binding States Description

   In addition to NO_BIND and BOUND from Section 6.2, three new states
   used in this process are listed here.  The INIT_BIND state is not
   used, as it is entered by observing a DHCP message.

   DETECTION: The address in the entry is undergoing local duplication
   detection.

   RECOVERY: The SAVI device is querying the assignment and lease time
   of the address in the entry through DHCP Leasequery.

   VERIFY: The SAVI device is verifying that the device connected to the
   attachment point has a hardware address that matches the one returned
   in the DHCP Leasequery.

   Because the mechanisms used for the operations carried out while the
   binding is in these three states operate over unreliable protocols,
   each operation is carried out twice with a timeout that is triggered
   if no response is received.

7.4.  Events

   To handle the Data Snooping Process, six extra events, described
   here, are needed in addition to those used by the DHCP Snooping
   Process (see Section 6.3).  If an event will trigger the creation of
   a new binding entry, the binding entry limit on the binding anchor
   MUST NOT be exceeded.

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   EVE_DATA_UNMATCH: A data packet without a matched binding is
   received.

   EVE_DATA_CONFLICT: An ARP Reply / Neighbor Advertisement (NA) message
   against an address in the DETECTION state is received from a host
   other than the one for which the entry was added (i.e., a host
   attached at a point other than the one on which the triggering data
   packet was received).

   EVE_DATA_LEASEQUERY:

   o  IPv4: A DHCPLEASEACTIVE message with the IP Address Lease Time
      option is received.  Note that the DHCPLEASEUNKNOWN and
      DHCPLEASEUNASSIGNED replies are ignored.

   o  IPv6: A successful LEASEQUERY-REPLY is received.

   EVE_DATA_VERIFY: An ARP Reply / NA message has been received in the
   VERIFY state from the device connected to the attachment point on
   which the data packet was received.

   The triggering packet should pass the following checks to trigger a
   valid event:

   o  Attribute check: the data packet should be from attachments with
      the Data-Snooping attribute; the DHCPLEASEACTIVE/LEASEQUERY-REPLY
      messages should be from attachments with the DHCP-Snooping
      attribute.

   o  Binding limitation check: the data messages must not cause new
      binding setup on an attachment whose binding entry limitation has
      been reached (refer to Section 11.5).

   o  Address check: For EVE_DATA_LEASEQUERY, the source address of the
      DHCPLEASEQUERY messages must pass the check specified in
      Section 8.2.  For EVE_DATA_CONFLICT and EVE_DATA_VERIFY, the
      source address and target address of the ARP or NA messages must
      pass the check specified in Section 8.2.

   o  Interval check: the interval between two successive
      EVE_DATA_UNMATCH events triggered by an attachment MUST be no
      smaller than DATA_SNOOPING_INTERVAL.

   o  TID check: the DHCPLEASEACTIVE/LEASEQUERY-REPLY messages must have
      a matched TID with the corresponding entry.

   o  Prefix check: the source address of the data packet should be of a
      valid local prefix, as specified in Section 7 of [RFC7039].

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   EVE_DATA_EXPIRE: A timer expires indicating that a response to a
   hardware address verification message sent in the VERIFY state has
   not been received within the specified DETECTION_TIMEOUT period.

   EVE_ENTRY_EXPIRE: A timer expires after the Lifetime indicated in the
   relevant BST entry has elapsed.  This is identical to the usage in
   the DHCP Snooping Process.

7.5.  Message Sender Functions

   The Data Snooping Process involves sending three different messages
   to other network devices.  Each message may be sent up to two times
   since they are sent over unreliable transports and are sent in
   different states.  The functions defined in this section specify the
   messages to be sent in the three cases.  In each case, the message to
   be sent depends on whether the triggering data packet is an IPv4 or
   an IPv6 packet.

7.5.1.  Duplicate Detection Message Sender

   Send a message to check if the source address in the data packet that
   triggered the Data Snooping Process has a local conflict (that is, it
   uses an address that is being used by another node):

   IPv4 address:  Broadcast an Address Resolution Protocol (ARP) Request
         [RFC826] or an ARP Probe [RFC5227] for the address to the local
         network.  An ARP Response will be expected from the device on
         the attachment point on which the triggering data packet was
         received.  An ARP Reply received on any other port indicates a
         duplicate address.

   IPv6 address:  Send a Duplicate Address Detection (DAD) message
         (Neighbor Solicitation message) to the solicited-node multicast
         address [RFC4861] targeting the address.  Ideally, only the
         host on that point of attachment responds with a Neighbor
         Advertisement.  A Neighbor Advertisement received on any other
         port indicates a duplicate address.

   As both the ARP and DAD processes are unreliable (the packet either
   to or from the other system may be lost in transit; see [RFC6620]),
   if there is no response after the DETECTION_TIMEOUT, an
   EVE_ENTRY_EXPIRE is generated.

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7.5.2.  Leasequery Message Sender

   Send a DHCPLEASEQUERY message to the DHCP server(s) to determine if
   it has given out a lease for the source address in the triggering
   data packet.  A list of authorized DHCP servers is kept by the SAVI
   device.  The list should be either preconfigured with the IPv4 and/or
   IPv6 addresses or dynamically discovered: For networks using IPv4,
   this can be done by sending DHCPv4 Discover messages and parsing the
   returned DHCPv4 Offer messages; for networks using IPv6, discovery
   can be done by sending DHCPv6 SOLICIT messages and parsing the
   returned ADVERTISE messages.  The same TID should be used for all
   LEASEQUERY messages sent in response to a triggering data message on
   an attachment point.  The TID is generated if the TID field in the
   BST entry is empty and recorded in the TID field of the BST entry
   when the first message is sent.  Subsequent messages use the TID from
   the BST entry.

   (1)  IPv4 address: Send a DHCPLEASEQUERY [RFC4388] message querying
        by IP address to each DHCPv4 server in the list of authorized
        servers with an IP Address Lease Time option (option 51).  If
        the server has a valid lease for the address, the requested
        information will be returned in a DHCPLEASEACTIVE message.

   (2)  IPv6 address: Send a LEASEQUERY [RFC5007] message querying by IP
        address to each DHCPv6 server in the list of authorized servers
        using the server address as the link-address in the LEASEQUERY
        message.  If the server has a valid lease for the address, the
        requested information will be returned in a LEASEQUERY-REPLY
        message marked as successful (i.e., without an
        OPTION_STATUS_CODE in the reply).  The IA Address option(s)
        returned contains any IPv6 addresses bound to the same link
        together with the lease validity time.

   As DHCP Leasequeries are an unreliable process (the packet either to
   or from the server may be lost in transit), if there is no response
   after the MAX_LEASEQUERY_DELAY, an EVE_DATA_EXPIRE is generated.
   Note that multiple response messages may be received if the list of
   authorized servers contains more than one address of the appropriate
   type and, in the case of DHCPv6, the responses may contain additional
   addresses for which leases have been allocated.

7.5.3.  Address Verification Message Sender

   Send a message to verify that the link-layer address in the attached
   device that sent the triggering data packet matches the link-layer
   address contained in the leasequery response:

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   IPv4 address:  Send an ARP Request with the Target Protocol Address
         set to the IP address in the BST entry.  The ARP Request is
         only sent to the attachment that triggered the binding.  If the
         attached device has the IP address bound to the interface
         attached to the SAVI device, an ARP Reply should be received
         containing the hardware address of the interface on the
         attached device that can be compared with the leasequery value.

   IPv6 address:  Send a Neighbor Solicitation (NS) message with the
         target address set to the IP address in the BST entry.  The NS
         is only sent to the attachment that triggered the binding.  If
         the attached device has the IP address bound to the interface
         attached to the SAVI device, an NA should be received
         indicating that the attached device has the IP address
         configured on the interface.

   As both the ARP and NS/NA processes are unreliable (the packet either
   to or from the other system may be lost in transit; see [RFC6620]),
   if there is no response after the DETECTION_TIMEOUT, an
   EVE_DATA_EXPIRE is generated.

7.6.  Initial State: NO_BIND

7.6.1.  Event: EVE_DATA_UNMATCH: A data packet without a matched binding
        is received

   Make a probabilistic determination as to whether to act on this
   event.  The probability may be configured or calculated based on the
   state of the SAVI device.  This probability should be low enough to
   mitigate the damage from DoS attacks against this process.

   Create a new entry in the BST.  Set the Binding Anchor field to the
   corresponding binding anchor of the attachment.  Set the Address
   field to the source address of the packet.

   Address conflicts MUST be detected and prevented.

   If local address detection is performed:
         Set the State field to DETECTION.  Set the Lifetime of the
         created entry to DETECTION_TIMEOUT.  Set the Timeouts field to
         0.  Start the detection of any local address conflicts by
         sending a Duplicate Address Detection Message (Section 7.5.1).
         Transition to DETECTION state.

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   If local address detection is not performed:
         Set the State field to RECOVERY.  Set the Lifetime of the
         created entry to LEASEQUERY_DELAY.  Set the Timeouts field to
         0.  Start the recovery of any DHCP lease associated with the
         source IP address by sending one or more LEASEQUERY messages
         (Section 7.5.2).  Transition to RECOVERY state.

   The packet that triggers this event SHOULD be discarded.

   An example of the BST entry during duplicate address detection is
   illustrated in Figure 11.

   +--------+-------+---------+-----------------------+-----+----------+
   | Anchor |Address|  State  | Lifetime              | TID | Timeouts |
   +--------+-------+---------+-----------------------+-----+----------+
   | Port_1 | Addr1 |DETECTION| DETECTION_TIMEOUT     |     |    0     |
   +--------+-------+---------+-----------------------+-----+----------+

     Figure 11: Binding Entry in BST on Data-Triggered Initialization

   Resulting state: DETECTION - The address in the entry is undergoing
   local duplication detection - or RECOVERY - The DHCP lease(s)
   associated with the address is being queried.

7.6.2.  Events Not Observed in NO_BIND for Data Snooping

   EVE_DATA_CONFLICT: An ARP Reply / NA message is received from an
   unexpected system.

   EVE_DATA_LEASEQUERY: A valid DHCPLEASEACTIVE or LEASEQUERY-REPLY is
   received.

   EVE_DATA_VERIFY: A valid ARP Reply or NA message is received from the
   attached device.

   All EVE_DHCP_* events defined in Section 6.3.2 are treated as
   described in the DHCP Snooping Process (Section 6.4.1) and may result
   in that process being triggered.

   EVE_ENTRY_EXPIRE: Expiration of the DECTECTION_TIMEOUT

   EVE_DATA_EXPIRE: Expiration of the DECTECTION_TIMEOUT

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7.7.  Initial State: DETECTION

7.7.1.  Event: EVE_ENTRY_EXPIRE

   When this event occurs, no address conflict has been detected during
   the previous DETECTION_TIMEOUT period.

   If the Timeouts field in the BST entry is 0:
         Set the Lifetime of the BST entry to DETECTION_TIMEOUT.  Set
         the Timeouts field to 1.  Restart the detection of any local
         address conflicts by sending a second Duplicate Address
         Detection Message (Section 7.5.1).  Remain in DETECTION state.

   If the Timeouts field in the BST entry is 1:

         Assume that there is no local address conflict.  Set the State
         field to RECOVERY.  Set the Lifetime of the BST entry to
         LEASEQUERY_DELAY.  Set the Timeouts field to 0.  Start the
         recovery of any DHCP lease associated with the source IP
         address by sending one or more LEASEQUERY messages
         (Section 7.5.2).  Transition to RECOVERY state.

   An example of the entry is illustrated in Figure 12.

   +--------+-------+----------+----------------------+-----+----------+
   | Anchor |Address|  State   | Lifetime             | TID | Timeouts |
   +--------+-------+----------+----------------------+-----+----------+
   | Port_1 | Addr1 | RECOVERY | MAX_LEASEQUERY_DELAY | TID |    0     |
   +--------+-------+----------+----------------------+-----+----------+

               Figure 12: Binding Entry in BST on Leasequery

   Resulting state: DETECTION - If a second local conflict period is
   required - or RECOVERY - The SAVI device is querying the assignment
   and lease time of the address in the entry through DHCP Leasequery.

7.7.2.  Event: EVE_DATA_CONFLICT: ARP Reply / NA Message Received from
        Unexpected System

   Remove the entry.

   Resulting state: NO_BIND - No binding has been set up.

7.7.3.  Events Not Observed in DETECTION

   EVE_DATA_UNMATCH: A data packet without a matched binding is received

   All EVE_DHCP_* events defined in Section 6.3.2

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   EVE_DHCP_REBIND: A DHCPv4 Rebind or a DHCPv6 Rebind message is
   received

7.8.  Initial State: RECOVERY

7.8.1.  Event: EVE_DATA_LEASEQUERY: A valid DHCPLEASEACTIVE or
        successful LEASEQUERY-REPLY is received

   Set the State in the BST entry to VERIFY.  Depending on the type of
   triggering source IP address, process the received DHCP Leasequery
   response:

   IPv4 address:  Update the Lifetime field in the BST entry to the sum
         of the value encoded in the IP Address Lease Time option of the
         DHCPLEASEACTIVE message and MAX_DHCP_RESPONSE_TIME.  Record the
         value of the "chaddr" field (hardware address) in the message
         for checking against the hardware address received during
         verification in the next state.  Set the Timeouts field to 0.
         Start the verification process by sending an Address
         Verification Message (see Section 7.5.3).  Transition to VERIFY
         state.  Start an additional verification timer with a duration
         of DETECTION_TIMEOUT.  When this expires, an EVE_DATA_EXPIRE
         event will be generated.

   IPv6 address:  Update the Lifetime field in the BST entry to the sum
         of the valid lifetime extracted from the OPTION_CLIENT_DATA
         option in the LEASEQUERY-REPLY message and
         MAX_DHCP_RESPONSE_TIME.  Set the Timeouts field to 0.  Start
         the verification process by sending an Address Verification
         Message (see Section 7.5.3).  Transition to VERIFY state.
         Start an additional verification timer with a duration of
         DETECTION_TIMEOUT.  When this expires, an EVE_DATA_EXPIRE event
         will be generated.

         If multiple addresses are received in the LEASEQUERY-REPLY, new
         BST entries MUST be created for the additional addresses using
         the same binding anchor.  The entries are created with state
         set to VERIFY and the other fields set as described in this
         section for the triggering source IP address.  Also, start the
         verification process and start verification timers for each
         additional address.

   Resulting state: VERIFY - Awaiting verification or otherwise of the
   association of the IP address with the connected interface.

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7.8.2.  Event: EVE_ENTRY_EXPIRE

   Depending on the value of the Timeouts field in the BST entry, either
   send repeat LEASEQUERY messages or discard the binding:

   If the Timeouts field in the BST entry is 0:
         No responses to the LEASEQUERY message(s) sent have been
         received during the first LEASEQUERY_DELAY period.  Set the
         Lifetime of the BST entry to LEASEQUERY_DELAY.  Set the
         Timeouts field to 1.  Restart the recovery of any DHCP lease
         associated with the source IP address by sending one or more
         LEASEQUERY messages (Section 7.5.2).  Remain in RECOVERY state.

   If the Timeouts field in the BST entry is 1:
         No responses to the LEASEQUERY messages sent during two
         LEASEQUERY_DELAY periods were received.  Assume that no leases
         exist and hence that the source IP address is bogus.  Delete
         the BST entry.  Transition to NO_BIND state.

   Resulting state: RECOVERY - If repeat leasequeries are sent - or
   NO_BIND - If no successful responses to LEASEQUERY messages have been
   received.

7.8.3.  Events Not Observed in RECOVERY

   EVE_DATA_UNMATCH: A data packet without a matched binding is received

   EVE_DATA_CONFLICT: An ARP Reply / NA message is received from an
   unexpected system

   EVE_DATA_VERIFY: A valid ARP Reply or NA message is received from the
   attached device

   All EVE_DHCP_* events defined in Section 6.3.2

   EVE_DATA_EXPIRE: Expiration of the DECTECTION_TIMEOUT

7.9.  Initial State: VERIFY

7.9.1.  Event: EVE_DATA_LEASEQUERY: A valid DHCPLEASEACTIVE or
        successful LEASEQUERY-REPLY is received

   If LEASEQUERY messages were sent to more than one DHCP server during
   RECOVERY state, additional successful leasequery responses may be
   received relating to the source IP address.  The conflict resolution
   mechanisms specified in Section 6.8 of [RFC4388] and Section 4.3.4 of
   [RFC5007] can be used to determine the message from which values are
   used to update the BST Lifetime entry and the hardware address

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   obtained from DHCP, as described in Section 7.8.1.  In the case of
   DHCPv6 queries, the LEASEQUERY-REPLY may contain additional addresses
   as described in Section 7.8.1.  If so, additional BST entries MUST be
   created or ones previously created updated as described in that
   section.

   Resulting state: VERIFY (no change).

7.9.2.  Event: EVE_DATA_VERIFY: A valid ARP Reply or NA is received from
        the device attached via the binding anchor

   Depending on the type of triggering source IP address, this event may
   indicate that the device attached via the binding anchor in the BST
   entry is configured by DHCP using the IP address:

   IPv4 address:  Check that the value of the sender hardware address in
         the ARP Reply matches the saved "chaddr" field (hardware
         address) from the previously received DHCPLEASEACTIVE message.
         If not, ignore this event; a subsequent retry may provide
         verification.  If the hardware addresses match, the binding
         entry has been verified.

   IPv6 address:  Simple receipt of a valid NA from the triggering
         source IP address at the binding anchor port provides
         verification for the binding entry.

   If the binding entry has been verified, set the state in the BST
   entry to BOUND.  Clear the TID field.  Cancel the verification timer.

   Resulting state: VERIFY (no change) - If the IPv4 DHCPLEASEQUERY
   "chaddr" address does not match the ARP Reply hardware address.
   Otherwise, the resulting state is BOUND.

7.9.3.  Event: EVE_ENTRY_EXPIRE

   The DHCP lease lifetime has expired before the entry could be
   verified.  Remove the entry.  Transition to NO_BIND state.

   Resulting state: NO_BIND - No binding has been set up.

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7.9.4.  Event: EVE_DATA_EXPIRE

   Depending on the value of the Timeouts field in the BST entry, either
   send a repeat validation message or discard the binding:

   If the Timeouts field in the BST entry is 0:
         No response to the verification message sent has been received
         during the first DETECTION_TIMEOUT period.  Set the Timeouts
         field to 1.  Restart the verification process by sending an
         Address Verification Message (see Section 7.5.3).  Start a
         verification timer with a duration of DETECTION_TIMEOUT.  When
         this expires, an EVE_DATA_EXPIRE event will be generated.
         Remain in VERIFY state.

   If the Timeouts field in the BST entry is 1:
         No responses to the verification messages sent during two
         DETECTION_TIMEOUT periods were received.  Assume that the
         configuration of the triggering source IP address cannot be
         verified and hence that the source IP address is bogus.  Delete
         the BST entry.  Transition to NO_BIND state.

   Resulting state: VERIFY - Additional verification message sent - or
   NO_BIND - No binding has been set up.

7.9.5.  Events Not Observed in VERIFY

   EVE_DATA_UNMATCH: A data packet without a matched binding is received

   EVE_DATA_CONFLICT: An ARP Reply / NA message is received from an
   unexpected system

   All EVE_DHCP_* events defined in Section 6.3.2

7.10.  Initial State: BOUND

   Upon entry to the BOUND state, control of the system continues as if
   a DHCP message assigning the address has been observed, as in
   Section 6.4.3.  The BST entry has been restored.

   Note that the TID field contains no value after the binding state
   changes to BOUND.  The TID field is recovered from snooping DHCP
   Renew/Rebind messages if these are observed as described in the DHCP
   Snooping Process.  Because TID is used to associate binding entries
   with messages from DHCP servers, it must be recovered or else a
   number of state transitions of this mechanism will not be executed
   normally.

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7.11.  Table of State Machine

   The main state transitions are listed as follows.

   State      Event               Action                      Next State
   ---------------------------------------------------------------------
   NO_BIND    EVE_DATA_UNMATCH    Start duplicate detect       DETECTION

   DETECTION  EVE_ENTRY_EXPIRE 1  Repeat duplicate detect      DETECTION

   DETECTION  EVE_ENTRY_EXPIRE 2  Start leasequery              RECOVERY

   DETECTION  EVE_DATA_CONFLICT   Remove entry                   NO_BIND

   RECOVERY   EVE_ENTRY_EXPIRE 1  Repeat leasequery             RECOVERY

   RECOVERY   EVE_ENTRY_EXPIRE 2  No lease found; remove entry   NO_BIND

   RECOVERY   EVE_DATA_LEASEQUERY Set lease time; start verify    VERIFY

   VERIFY     EVE_ENTRY_EXPIRE    Lease expiry; remove entry     NO_BIND

   VERIFY     EVE_DATA_LEASEQUERY Resolve lease conflict(s)       VERIFY

   VERIFY     EVE_DATA_VERIFY     Finish validation     BOUND or NO_BIND

   VERIFY     EVE_DATA_EXPIRE 1   Repeat verify                   VERIFY

   VERIFY     EVE_DATA_EXPIRE 2   Verify failed; remove entry    NO_BIND

   BOUND      EVE_ENTRY_EXPIRE    Lease expiry; remove entry     NO_BIND

   BOUND      RENEW/REBIND        Record TID                       BOUND

                     Figure 13: State Transition Table

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                               +-------------+         EVE_ENTRY_EXPIRE
                     /---------+             |<------------------------\
                     |         |   NO_BIND   |         EVE_DATA_EXPIRE |
    EVE_DATA_UNMATCH |  /----->|             |<----\   (2nd VRF_DELAY) |
                     |  |      +-------------+     |                   |
                     |  |         EVE_ENTRY_EXPIRE |                   |
                     |  |           (2nd LQ_DELAY) |                   |
   EVE_ENTRY_EXPIRE  |  |                          |  EVE_ENTRY_EXPIRE |
   (1st DAD_DELAY)   |  |                          |   (1st LQ_DELAY)  |
         /------\    |  |                          |        /--------\ |
         |      |    |  | EVE_DATA_CONFLICT        \---\    |        | |
         |      v    v  |                              |    v        | |
         |    +-------------+ EVE_ENTRY_EXPIRE       +------------+  | |
         |    |             | (2nd DAD_DELAY)        |            |  | |
         \----+  DETECTION  ------------------------>|  RECOVERY  +--/ |
              |             |                        |            |    |
              +-------------+   (To NO_BIND)         +------------+    |
                                ^                               |      |
                                |           EVE_DATA_LEASEQUERY |      |
                  /----------\  |                               |      |
                  |          |  | EVE_ENTRY_EXPIRE              |      |
    EVE_DHCP_RENEW|          v  |                               v      |
   EVE_DHCP_REBIND|    +-------------+                +-------------+  |
                  |    |             |                |             +--/
                  \----+   BOUND     |<---------------+   VERIFY    |
                       |             | EVE_DATA_VERIFY|             |<-\
                       +-------------+                +-------------+  |
                                                            |          |
                                                            \----------/
                                                     EVE_DATA_LEASEQUERY
                                                         EVE_DATA_EXPIRE
                                                         (1st VRF_DELAY)

                       Figure 14: Diagram of Transit

   LQ_DELAY:  MAX_LEASEQUERY_DELAY
   VRF_DELAY: DETECTION_TIMEOUT



(page 45 continued on part 3)

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