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RFC 4271

 
 
 

A Border Gateway Protocol 4 (BGP-4)

Part 3 of 4, p. 36 to 75
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7.  BGP Version Negotiation

   BGP speakers MAY negotiate the version of the protocol by making
   multiple attempts at opening a BGP connection, starting with the
   highest version number each BGP speaker supports.  If an open attempt
   fails with an Error Code, OPEN Message Error, and an Error Subcode,
   Unsupported Version Number, then the BGP speaker has available the
   version number it tried, the version number its peer tried, the
   version number passed by its peer in the NOTIFICATION message, and
   the version numbers it supports.  If the two peers do support one or
   more common versions, then this will allow them to rapidly determine
   the highest common version.  In order to support BGP version
   negotiation, future versions of BGP MUST retain the format of the
   OPEN and NOTIFICATION messages.

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8.  BGP Finite State Machine (FSM)

   The data structures and FSM described in this document are conceptual
   and do not have to be implemented precisely as described here, as
   long as the implementations support the described functionality and
   they exhibit the same externally visible behavior.

   This section specifies the BGP operation in terms of a Finite State
   Machine (FSM).  The section falls into two parts:

      1) Description of Events for the State machine (Section 8.1)
      2) Description of the FSM (Section 8.2)

   Session attributes required (mandatory) for each connection are:

      1) State
      2) ConnectRetryCounter
      3) ConnectRetryTimer
      4) ConnectRetryTime
      5) HoldTimer
      6) HoldTime
      7) KeepaliveTimer
      8) KeepaliveTime

   The state session attribute indicates the current state of the BGP
   FSM.  The ConnectRetryCounter indicates the number of times a BGP
   peer has tried to establish a peer session.

   The mandatory attributes related to timers are described in Section
   10.  Each timer has a "timer" and a "time" (the initial value).

   The optional Session attributes are listed below.  These optional
   attributes may be supported, either per connection or per local
   system:

      1) AcceptConnectionsUnconfiguredPeers
      2) AllowAutomaticStart
      3) AllowAutomaticStop
      4) CollisionDetectEstablishedState
      5) DampPeerOscillations
      6) DelayOpen
      7) DelayOpenTime
      8) DelayOpenTimer
      9) IdleHoldTime
     10) IdleHoldTimer
     11) PassiveTcpEstablishment
     12) SendNOTIFICATIONwithoutOPEN
     13) TrackTcpState

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   The optional session attributes support different features of the BGP
   functionality that have implications for the BGP FSM state
   transitions.  Two groups of the attributes which relate to timers
   are:

      group 1: DelayOpen, DelayOpenTime, DelayOpenTimer
      group 2: DampPeerOscillations, IdleHoldTime, IdleHoldTimer

   The first parameter (DelayOpen, DampPeerOscillations) is an optional
   attribute that indicates that the Timer function is active.  The
   "Time" value specifies the initial value for the "Timer"
   (DelayOpenTime, IdleHoldTime).  The "Timer" specifies the actual
   timer.

   Please refer to Section 8.1.1 for an explanation of the interaction
   between these optional attributes and the events signaled to the
   state machine.  Section 8.2.1.3 also provides a short overview of the
   different types of optional attributes (flags or timers).

8.1.  Events for the BGP FSM

8.1.1.  Optional Events Linked to Optional Session Attributes

   The Inputs to the BGP FSM are events.  Events can either be mandatory
   or optional.  Some optional events are linked to optional session
   attributes.  Optional session attributes enable several groups of FSM
   functionality.

   The linkage between FSM functionality, events, and the optional
   session attributes are described below.

      Group 1: Automatic Administrative Events (Start/Stop)

         Optional Session Attributes: AllowAutomaticStart,
                                      AllowAutomaticStop,
                                      DampPeerOscillations,
                                      IdleHoldTime, IdleHoldTimer

         Option 1:    AllowAutomaticStart

         Description: A BGP peer connection can be started and stopped
                      by administrative control.  This administrative
                      control can either be manual, based on operator
                      intervention, or under the control of logic that
                      is specific to a BGP implementation.  The term
                      "automatic" refers to a start being issued to the
                      BGP peer connection FSM when such logic determines
                      that the BGP peer connection should be restarted.

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                      The AllowAutomaticStart attribute specifies that
                      this BGP connection supports automatic starting of
                      the BGP connection.

                      If the BGP implementation supports
                      AllowAutomaticStart, the peer may be repeatedly
                      restarted.  Three other options control the rate
                      at which the automatic restart occurs:
                      DampPeerOscillations, IdleHoldTime, and the
                      IdleHoldTimer.

                      The DampPeerOscillations option specifies that the
                      implementation engages additional logic to damp
                      the oscillations of BGP peers in the face of
                      sequences of automatic start and automatic stop.
                      IdleHoldTime specifies the length of time the BGP
                      peer is held in the Idle state prior to allowing
                      the next automatic restart.  The IdleHoldTimer is
                      the timer that holds the peer in Idle state.

                      An example of DampPeerOscillations logic is an
                      increase of the IdleHoldTime value if a BGP peer
                      oscillates connectivity (connected/disconnected)
                      repeatedly within a time period.  To engage this
                      logic, a peer could connect and disconnect 10
                      times within 5 minutes.  The IdleHoldTime value
                      would be reset from 0 to 120 seconds.

         Values:      TRUE or FALSE

         Option 2:    AllowAutomaticStop

         Description: This BGP peer session optional attribute indicates
                      that the BGP connection allows "automatic"
                      stopping of the BGP connection.  An "automatic"
                      stop is defined as a stop under the control of
                      implementation-specific logic.  The
                      implementation-specific logic is outside the scope
                      of this specification.

         Values:      TRUE or FALSE

         Option 3:    DampPeerOscillations

         Description: The DampPeerOscillations optional session
                      attribute indicates that the BGP connection is
                      using logic that damps BGP peer oscillations in
                      the Idle State.

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         Value:       TRUE or FALSE

         Option 4:    IdleHoldTime

         Description: The IdleHoldTime is the value that is set in the
                      IdleHoldTimer.

         Values:      Time in seconds

         Option 5:    IdleHoldTimer

         Description: The IdleHoldTimer aids in controlling BGP peer
                      oscillation.  The IdleHoldTimer is used to keep
                      the BGP peer in Idle for a particular duration.
                      The IdleHoldTimer_Expires event is described in
                      Section 8.1.3.

         Values:      Time in seconds

      Group 2: Unconfigured Peers

         Optional Session Attributes: AcceptConnectionsUnconfiguredPeers

         Option 1:    AcceptConnectionsUnconfiguredPeers

         Description: The BGP FSM optionally allows the acceptance of
                      BGP peer connections from neighbors that are not
                      pre-configured.  The
                      "AcceptConnectionsUnconfiguredPeers" optional
                      session attribute allows the FSM to support the
                      state transitions that allow the implementation to
                      accept or reject these unconfigured peers.

                      The AcceptConnectionsUnconfiguredPeers has
                      security implications.  Please refer to the BGP
                      Vulnerabilities document [RFC4272] for details.

         Value:       True or False

      Group 3: TCP processing

         Optional Session Attributes: PassiveTcpEstablishment,
                                      TrackTcpState

         Option 1:    PassiveTcpEstablishment

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         Description: This option indicates that the BGP FSM will
                      passively wait for the remote BGP peer to
                      establish the BGP TCP connection.

         value:       TRUE or FALSE

         Option 2:    TrackTcpState

         Description: The BGP FSM normally tracks the end result of a
                      TCP connection attempt rather than individual TCP
                      messages.  Optionally, the BGP FSM can support
                      additional interaction with the TCP connection
                      negotiation.  The interaction with the TCP events
                      may increase the amount of logging the BGP peer
                      connection requires and the number of BGP FSM
                      changes.

         Value:       TRUE or FALSE

      Group 4:  BGP Message Processing

         Optional Session Attributes: DelayOpen, DelayOpenTime,
                                      DelayOpenTimer,
                                      SendNOTIFICATIONwithoutOPEN,
                                      CollisionDetectEstablishedState

         Option 1:     DelayOpen

         Description: The DelayOpen optional session attribute allows
                      implementations to be configured to delay sending
                      an OPEN message for a specific time period
                      (DelayOpenTime).  The delay allows the remote BGP
                      Peer time to send the first OPEN message.

         Value:       TRUE or FALSE

         Option 2:    DelayOpenTime

         Description: The DelayOpenTime is the initial value set in the
                      DelayOpenTimer.

         Value:       Time in seconds

         Option 3:    DelayOpenTimer

         Description: The DelayOpenTimer optional session attribute is
                      used to delay the sending of an OPEN message on a

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                      connection.  The DelayOpenTimer_Expires event
                      (Event 12) is described in Section 8.1.3.

         Value:       Time in seconds

         Option 4:    SendNOTIFICATIONwithoutOPEN

         Description: The SendNOTIFICATIONwithoutOPEN allows a peer to
                      send a NOTIFICATION without first sending an OPEN
                      message.  Without this optional session attribute,
                      the BGP connection assumes that an OPEN message
                      must be sent by a peer prior to the peer sending a
                      NOTIFICATION message.

         Value:       True or False

         Option 5:    CollisionDetectEstablishedState

         Description: Normally, a Detect Collision (see Section 6.8)
                      will be ignored in the Established state.  This
                      optional session attribute indicates that this BGP
                      connection processes collisions in the Established
                      state.

         Value:       True or False

      Note: The optional session attributes clarify the BGP FSM
            description for existing features of BGP implementations.
            The optional session attributes may be pre-defined for an
            implementation and not readable via management interfaces
            for existing correct implementations.  As newer BGP MIBs
            (version 2 and beyond) are supported, these fields will be
            accessible via a management interface.

8.1.2.  Administrative Events

   An administrative event is an event in which the operator interface
   and BGP Policy engine signal the BGP-finite state machine to start or
   stop the BGP state machine.  The basic start and stop indications are
   augmented by optional connection attributes that signal a certain
   type of start or stop mechanism to the BGP FSM.  An example of this
   combination is Event 5, AutomaticStart_with_PassiveTcpEstablishment.
   With this event, the BGP implementation signals to the BGP FSM that
   the implementation is using an Automatic Start with the option to use
   a Passive TCP Establishment.  The Passive TCP establishment signals
   that this BGP FSM will wait for the remote side to start the TCP
   establishment.

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   Note that only Event 1 (ManualStart) and Event 2 (ManualStop) are
   mandatory administrative events.  All other administrative events are
   optional (Events 3-8).  Each event below has a name, definition,
   status (mandatory or optional), and the optional session attributes
   that SHOULD be set at each stage.  When generating Event 1 through
   Event 8 for the BGP FSM, the conditions specified in the "Optional
   Attribute Status" section are verified.  If any of these conditions
   are not satisfied, then the local system should log an FSM error.

   The settings of optional session attributes may be implicit in some
   implementations, and therefore may not be set explicitly by an
   external operator action.  Section 8.2.1.5 describes these implicit
   settings of the optional session attributes.  The administrative
   states described below may also be implicit in some implementations
   and not directly configurable by an external operator.

      Event 1: ManualStart

         Definition: Local system administrator manually starts the peer
                     connection.

         Status:     Mandatory

         Optional
         Attribute
         Status:     The PassiveTcpEstablishment attribute SHOULD be set
                     to FALSE.

      Event 2: ManualStop

         Definition: Local system administrator manually stops the peer
                     connection.

         Status:     Mandatory

         Optional
         Attribute
         Status:     No interaction with any optional attributes.

      Event 3: AutomaticStart

         Definition: Local system automatically starts the BGP
                     connection.

         Status:     Optional, depending on local system

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         Optional
         Attribute
         Status:     1) The AllowAutomaticStart attribute SHOULD be set
                        to TRUE if this event occurs.
                     2) If the PassiveTcpEstablishment optional session
                        attribute is supported, it SHOULD be set to
                        FALSE.
                     3) If the DampPeerOscillations is supported, it
                        SHOULD be set to FALSE when this event occurs.

      Event 4: ManualStart_with_PassiveTcpEstablishment

         Definition: Local system administrator manually starts the peer
                     connection, but has PassiveTcpEstablishment
                     enabled.  The PassiveTcpEstablishment optional
                     attribute indicates that the peer will listen prior
                     to establishing the connection.

         Status:     Optional, depending on local system

         Optional
         Attribute
         Status:     1) The PassiveTcpEstablishment attribute SHOULD be
                        set to TRUE if this event occurs.
                     2) The DampPeerOscillations attribute SHOULD be set
                        to FALSE when this event occurs.

      Event 5: AutomaticStart_with_PassiveTcpEstablishment

         Definition: Local system automatically starts the BGP
                     connection with the PassiveTcpEstablishment
                     enabled.  The PassiveTcpEstablishment optional
                     attribute indicates that the peer will listen prior
                     to establishing a connection.

         Status:     Optional, depending on local system

         Optional
         Attribute
         Status:     1) The AllowAutomaticStart attribute SHOULD be set
                        to TRUE.
                     2) The PassiveTcpEstablishment attribute SHOULD be
                        set to TRUE.
                     3) If the DampPeerOscillations attribute is
                        supported, the DampPeerOscillations SHOULD be
                        set to FALSE.

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      Event 6: AutomaticStart_with_DampPeerOscillations

         Definition: Local system automatically starts the BGP peer
                     connection with peer oscillation damping enabled.
                     The exact method of damping persistent peer
                     oscillations is determined by the implementation
                     and is outside the scope of this document.

         Status:     Optional, depending on local system.

         Optional
         Attribute
         Status:     1) The AllowAutomaticStart attribute SHOULD be set
                        to TRUE.
                     2) The DampPeerOscillations attribute SHOULD be set
                        to TRUE.
                     3) The PassiveTcpEstablishment attribute SHOULD be
                        set to FALSE.

      Event 7: AutomaticStart_with_DampPeerOscillations_and_
      PassiveTcpEstablishment

         Definition: Local system automatically starts the BGP peer
                     connection with peer oscillation damping enabled
                     and PassiveTcpEstablishment enabled.  The exact
                     method of damping persistent peer oscillations is
                     determined by the implementation and is outside the
                     scope of this document.

         Status:     Optional, depending on local system

         Optional
         Attributes
         Status:     1) The AllowAutomaticStart attribute SHOULD be set
                        to TRUE.
                     2) The DampPeerOscillations attribute SHOULD be set
                        to TRUE.
                     3) The PassiveTcpEstablishment attribute SHOULD be
                        set to TRUE.

      Event 8: AutomaticStop

         Definition: Local system automatically stops the BGP
                     connection.

                     An example of an automatic stop event is exceeding
                     the number of prefixes for a given peer and the
                     local system automatically disconnecting the peer.

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         Status:     Optional, depending on local system

         Optional
         Attribute
         Status:     1) The AllowAutomaticStop attribute SHOULD be TRUE.

8.1.3.  Timer Events

      Event 9: ConnectRetryTimer_Expires

         Definition: An event generated when the ConnectRetryTimer
                     expires.

         Status:     Mandatory

      Event 10: HoldTimer_Expires

         Definition: An event generated when the HoldTimer expires.

         Status:     Mandatory

      Event 11: KeepaliveTimer_Expires

         Definition: An event generated when the KeepaliveTimer expires.

         Status:     Mandatory

      Event 12: DelayOpenTimer_Expires

         Definition: An event generated when the DelayOpenTimer expires.

                     Status:     Optional

         Optional
         Attribute
         Status:     If this event occurs,
                     1) DelayOpen attribute SHOULD be set to TRUE,
                     2) DelayOpenTime attribute SHOULD be supported,
                     3) DelayOpenTimer SHOULD be supported.

      Event 13: IdleHoldTimer_Expires

         Definition: An event generated when the IdleHoldTimer expires,
                     indicating that the BGP connection has completed
                     waiting for the back-off period to prevent BGP peer
                     oscillation.

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                     The IdleHoldTimer is only used when the persistent
                     peer oscillation damping function is enabled by
                     setting the DampPeerOscillations optional attribute
                     to TRUE.

                     Implementations not implementing the persistent
                     peer oscillation damping function may not have the
                     IdleHoldTimer.

         Status:     Optional

         Optional
         Attribute
         Status:     If this event occurs:
                     1) DampPeerOscillations attribute SHOULD be set to
                        TRUE.
                     2) IdleHoldTimer SHOULD have just expired.

8.1.4.  TCP Connection-Based Events

      Event 14: TcpConnection_Valid

         Definition: Event indicating the local system reception of a
                     TCP connection request with a valid source IP
                     address, TCP port, destination IP address, and TCP
                     Port.  The definition of invalid source and invalid
                     destination IP address is determined by the
                     implementation.

                     BGP's destination port SHOULD be port 179, as
                     defined by IANA.

                     TCP connection request is denoted by the local
                     system receiving a TCP SYN.

         Status:     Optional

         Optional
         Attribute
         Status:     1) The TrackTcpState attribute SHOULD be set to
                        TRUE if this event occurs.

      Event 15: Tcp_CR_Invalid

         Definition: Event indicating the local system reception of a
                     TCP connection request with either an invalid
                     source address or port number, or an invalid
                     destination address or port number.

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                     BGP destination port number SHOULD be 179, as
                     defined by IANA.

                     A TCP connection request occurs when the local
                     system receives a TCP SYN.

         Status:     Optional

         Optional
         Attribute
         Status:     1) The TrackTcpState attribute should be set to
                        TRUE if this event occurs.

      Event 16: Tcp_CR_Acked

         Definition: Event indicating the local system's request to
                     establish a TCP connection to the remote peer.

                     The local system's TCP connection sent a TCP SYN,
                     received a TCP SYN/ACK message, and sent a TCP ACK.

         Status:     Mandatory

      Event 17: TcpConnectionConfirmed

         Definition: Event indicating that the local system has received
                     a confirmation that the TCP connection has been
                     established by the remote site.

                     The remote peer's TCP engine sent a TCP SYN.  The
                     local peer's TCP engine sent a SYN, ACK message and
                     now has received a final ACK.

         Status:     Mandatory

      Event 18: TcpConnectionFails

         Definition: Event indicating that the local system has received
                     a TCP connection failure notice.

                     The remote BGP peer's TCP machine could have sent a
                     FIN.  The local peer would respond with a FIN-ACK.
                     Another possibility is that the local peer
                     indicated a timeout in the TCP connection and
                     downed the connection.

         Status:     Mandatory

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8.1.5.  BGP Message-Based Events

      Event 19: BGPOpen

         Definition: An event is generated when a valid OPEN message has
                     been received.

         Status:     Mandatory

         Optional
         Attribute
         Status:     1) The DelayOpen optional attribute SHOULD be set
                        to FALSE.
                     2) The DelayOpenTimer SHOULD not be running.

      Event 20: BGPOpen with DelayOpenTimer running

         Definition: An event is generated when a valid OPEN message has
                     been received for a peer that has a successfully
                     established transport connection and is currently
                     delaying the sending of a BGP open message.

         Status:     Optional

         Optional
         Attribute
         Status:     1) The DelayOpen attribute SHOULD be set to TRUE.
                     2) The DelayOpenTimer SHOULD be running.

      Event 21: BGPHeaderErr

         Definition: An event is generated when a received BGP message
                     header is not valid.

         Status:     Mandatory

      Event 22: BGPOpenMsgErr

         Definition: An event is generated when an OPEN message has been
                     received with errors.

         Status:     Mandatory

      Event 23: OpenCollisionDump

         Definition: An event generated administratively when a
                     connection collision has been detected while
                     processing an incoming OPEN message and this

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                     connection has been selected to be disconnected.
                     See Section 6.8 for more information on collision
                     detection.

                     Event 23 is an administrative action generated by
                     implementation logic that determines whether this
                     connection needs to be dropped per the rules in
                     Section 6.8.  This event may occur if the FSM is
                     implemented as two linked state machines.

         Status:     Optional

         Optional
         Attribute
         Status:     If the state machine is to process this event in
                     the Established state,
                     1) CollisionDetectEstablishedState optional
                        attribute SHOULD be set to TRUE.

                     Please note: The OpenCollisionDump event can occur
                     in Idle, Connect, Active, OpenSent, and OpenConfirm
                     without any optional attributes being set.

      Event 24: NotifMsgVerErr

         Definition: An event is generated when a NOTIFICATION message
                     with "version error" is received.

         Status:     Mandatory

      Event 25: NotifMsg

         Definition: An event is generated when a NOTIFICATION message
                     is received and the error code is anything but
                     "version error".

         Status:     Mandatory

      Event 26: KeepAliveMsg

         Definition: An event is generated when a KEEPALIVE message is
                     received.

         Status:     Mandatory

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      Event 27: UpdateMsg

         Definition: An event is generated when a valid UPDATE message
                     is received.

         Status:     Mandatory

      Event 28: UpdateMsgErr

         Definition: An event is generated when an invalid UPDATE
                     message is received.

         Status:     Mandatory

8.2.  Description of FSM

8.2.1.  FSM Definition

   BGP MUST maintain a separate FSM for each configured peer.  Each BGP
   peer paired in a potential connection will attempt to connect to the
   other, unless configured to remain in the idle state, or configured
   to remain passive.  For the purpose of this discussion, the active or
   connecting side of the TCP connection (the side of a TCP connection
   sending the first TCP SYN packet) is called outgoing.  The passive or
   listening side (the sender of the first SYN/ACK) is called an
   incoming connection.  (See Section 8.2.1.1 for information on the
   terms active and passive used below.)

   A BGP implementation MUST connect to and listen on TCP port 179 for
   incoming connections in addition to trying to connect to peers.  For
   each incoming connection, a state machine MUST be instantiated.
   There exists a period in which the identity of the peer on the other
   end of an incoming connection is known, but the BGP identifier is not
   known.  During this time, both an incoming and outgoing connection
   may exist for the same configured peering.  This is referred to as a
   connection collision (see Section 6.8).

   A BGP implementation will have, at most, one FSM for each configured
   peering, plus one FSM for each incoming TCP connection for which the
   peer has not yet been identified.  Each FSM corresponds to exactly
   one TCP connection.

   There may be more than one connection between a pair of peers if the
   connections are configured to use a different pair of IP addresses.
   This is referred to as multiple "configured peerings" to the same
   peer.

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8.2.1.1.  Terms "active" and "passive"

   The terms active and passive have been in the Internet operator's
   vocabulary for almost a decade and have proven useful.  The words
   active and passive have slightly different meanings when applied to a
   TCP connection or a peer.  There is only one active side and one
   passive side to any one TCP connection, per the definition above and
   the state machine below.  When a BGP speaker is configured as active,
   it may end up on either the active or passive side of the connection
   that eventually gets established.  Once the TCP connection is
   completed, it doesn't matter which end was active and which was
   passive.  The only difference is in which side of the TCP connection
   has port number 179.

8.2.1.2.  FSM and Collision Detection

   There is one FSM per BGP connection.  When the connection collision
   occurs prior to determining what peer a connection is associated
   with, there may be two connections for one peer.  After the
   connection collision is resolved (see Section 6.8), the FSM for the
   connection that is closed SHOULD be disposed.

8.2.1.3.  FSM and Optional Session Attributes

   Optional Session Attributes specify either attributes that act as
   flags (TRUE or FALSE) or optional timers.  For optional attributes
   that act as flags, if the optional session attribute can be set to
   TRUE on the system, the corresponding BGP FSM actions must be
   supported.  For example, if the following options can be set in a BGP
   implementation: AutoStart and PassiveTcpEstablishment, then Events 3,
   4 and 5 must be supported.  If an Optional Session attribute cannot
   be set to TRUE, the events supporting that set of options do not have
   to be supported.

   Each of the optional timers (DelayOpenTimer and IdleHoldTimer) has a
   group of attributes that are:

      - flag indicating support,
      - Time set in Timer
      - Timer.

   The two optional timers show this format:

      DelayOpenTimer: DelayOpen, DelayOpenTime, DelayOpenTimer
      IdleHoldTimer:  DampPeerOscillations, IdleHoldTime,
                      IdleHoldTimer

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   If the flag indicating support for an optional timer (DelayOpen or
   DampPeerOscillations) cannot be set to TRUE, the timers and events
   supporting that option do not have to be supported.

8.2.1.4.  FSM Event Numbers

   The Event numbers (1-28) utilized in this state machine description
   aid in specifying the behavior of the BGP state machine.
   Implementations MAY use these numbers to provide network management
   information.  The exact form of an FSM or the FSM events are specific
   to each implementation.

8.2.1.5.  FSM Actions that are Implementation Dependent

   At certain points, the BGP FSM specifies that BGP initialization will
   occur or that BGP resources will be deleted.  The initialization of
   the BGP FSM and the associated resources depend on the policy portion
   of the BGP implementation.  The details of these actions are outside
   the scope of the FSM document.

8.2.2.  Finite State Machine

   Idle state:

      Initially, the BGP peer FSM is in the Idle state.  Hereafter, the
      BGP peer FSM will be shortened to BGP FSM.

      In this state, BGP FSM refuses all incoming BGP connections for
      this peer.  No resources are allocated to the peer.  In response
      to a ManualStart event (Event 1) or an AutomaticStart event (Event
      3), the local system:

        - initializes all BGP resources for the peer connection,

        - sets ConnectRetryCounter to zero,

        - starts the ConnectRetryTimer with the initial value,

        - initiates a TCP connection to the other BGP peer,

        - listens for a connection that may be initiated by the remote
          BGP peer, and

        - changes its state to Connect.

      The ManualStop event (Event 2) and AutomaticStop (Event 8) event
      are ignored in the Idle state.

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      In response to a ManualStart_with_PassiveTcpEstablishment event
      (Event 4) or AutomaticStart_with_PassiveTcpEstablishment event
      (Event 5), the local system:

        - initializes all BGP resources,

        - sets the ConnectRetryCounter to zero,

        - starts the ConnectRetryTimer with the initial value,

        - listens for a connection that may be initiated by the remote
          peer, and

        - changes its state to Active.

      The exact value of the ConnectRetryTimer is a local matter, but it
      SHOULD be sufficiently large to allow TCP initialization.

      If the DampPeerOscillations attribute is set to TRUE, the
      following three additional events may occur within the Idle state:

        - AutomaticStart_with_DampPeerOscillations (Event 6),

        - AutomaticStart_with_DampPeerOscillations_and_
          PassiveTcpEstablishment (Event 7),

        - IdleHoldTimer_Expires (Event 13).

      Upon receiving these 3 events, the local system will use these
      events to prevent peer oscillations.  The method of preventing
      persistent peer oscillation is outside the scope of this document.

      Any other event (Events 9-12, 15-28) received in the Idle state
      does not cause change in the state of the local system.

   Connect State:

      In this state, BGP FSM is waiting for the TCP connection to be
      completed.

      The start events (Events 1, 3-7) are ignored in the Connect state.

      In response to a ManualStop event (Event 2), the local system:

        - drops the TCP connection,

        - releases all BGP resources,

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        - sets ConnectRetryCounter to zero,

        - stops the ConnectRetryTimer and sets ConnectRetryTimer to
          zero, and

        - changes its state to Idle.

      In response to the ConnectRetryTimer_Expires event (Event 9), the
      local system:

        - drops the TCP connection,

        - restarts the ConnectRetryTimer,

        - stops the DelayOpenTimer and resets the timer to zero,

        - initiates a TCP connection to the other BGP peer,

        - continues to listen for a connection that may be initiated by
          the remote BGP peer, and

        - stays in the Connect state.

      If the DelayOpenTimer_Expires event (Event 12) occurs in the
      Connect state, the local system:

        - sends an OPEN message to its peer,

        - sets the HoldTimer to a large value, and

        - changes its state to OpenSent.

      If the BGP FSM receives a TcpConnection_Valid event (Event 14),
      the TCP connection is processed, and the connection remains in the
      Connect state.

      If the BGP FSM receives a Tcp_CR_Invalid event (Event 15), the
      local system rejects the TCP connection, and the connection
      remains in the Connect state.

      If the TCP connection succeeds (Event 16 or Event 17), the local
      system checks the DelayOpen attribute prior to processing.  If the
      DelayOpen attribute is set to TRUE, the local system:

        - stops the ConnectRetryTimer (if running) and sets the
          ConnectRetryTimer to zero,

        - sets the DelayOpenTimer to the initial value, and

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        - stays in the Connect state.

      If the DelayOpen attribute is set to FALSE, the local system:

        - stops the ConnectRetryTimer (if running) and sets the
          ConnectRetryTimer to zero,

        - completes BGP initialization

        - sends an OPEN message to its peer,

        - sets the HoldTimer to a large value, and

        - changes its state to OpenSent.

      A HoldTimer value of 4 minutes is suggested.

      If the TCP connection fails (Event 18), the local system checks
      the DelayOpenTimer.  If the DelayOpenTimer is running, the local
      system:

        - restarts the ConnectRetryTimer with the initial value,

        - stops the DelayOpenTimer and resets its value to zero,

        - continues to listen for a connection that may be initiated by
          the remote BGP peer, and

        - changes its state to Active.

      If the DelayOpenTimer is not running, the local system:

        - stops the ConnectRetryTimer to zero,

        - drops the TCP connection,

        - releases all BGP resources, and

        - changes its state to Idle.

      If an OPEN message is received while the DelayOpenTimer is running
      (Event 20), the local system:

        - stops the ConnectRetryTimer (if running) and sets the
          ConnectRetryTimer to zero,

        - completes the BGP initialization,

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        - stops and clears the DelayOpenTimer (sets the value to zero),

        - sends an OPEN message,

        - sends a KEEPALIVE message,

        - if the HoldTimer initial value is non-zero,

            - starts the KeepaliveTimer with the initial value and

            - resets the HoldTimer to the negotiated value,

          else, if the HoldTimer initial value is zero,

            - resets the KeepaliveTimer and

            - resets the HoldTimer value to zero,

        - and changes its state to OpenConfirm.

      If the value of the autonomous system field is the same as the
      local Autonomous System number, set the connection status to an
      internal connection; otherwise it will be "external".

      If BGP message header checking (Event 21) or OPEN message checking
      detects an error (Event 22) (see Section 6.2), the local system:

        - (optionally) If the SendNOTIFICATIONwithoutOPEN attribute is
          set to TRUE, then the local system first sends a NOTIFICATION
          message with the appropriate error code, and then

        - stops the ConnectRetryTimer (if running) and sets the
          ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

      If a NOTIFICATION message is received with a version error (Event
      24), the local system checks the DelayOpenTimer.  If the
      DelayOpenTimer is running, the local system:

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        - stops the ConnectRetryTimer (if running) and sets the
          ConnectRetryTimer to zero,

        - stops and resets the DelayOpenTimer (sets to zero),

        - releases all BGP resources,

        - drops the TCP connection, and

        - changes its state to Idle.

      If the DelayOpenTimer is not running, the local system:

        - stops the ConnectRetryTimer and sets the ConnectRetryTimer to
          zero,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

        - performs peer oscillation damping if the DampPeerOscillations
          attribute is set to True, and

        - changes its state to Idle.

      In response to any other events (Events 8, 10-11, 13, 19, 23,
      25-28), the local system:

        - if the ConnectRetryTimer is running, stops and resets the
          ConnectRetryTimer (sets to zero),

        - if the DelayOpenTimer is running, stops and resets the
          DelayOpenTimer (sets to zero),

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

        - performs peer oscillation damping if the DampPeerOscillations
          attribute is set to True, and

        - changes its state to Idle.

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   Active State:

      In this state, BGP FSM is trying to acquire a peer by listening
      for, and accepting, a TCP connection.

      The start events (Events 1, 3-7) are ignored in the Active state.

      In response to a ManualStop event (Event 2), the local system:

        - If the DelayOpenTimer is running and the
          SendNOTIFICATIONwithoutOPEN session attribute is set, the
          local system sends a NOTIFICATION with a Cease,

        - releases all BGP resources including stopping the
          DelayOpenTimer

        - drops the TCP connection,

        - sets ConnectRetryCounter to zero,

        - stops the ConnectRetryTimer and sets the ConnectRetryTimer to
          zero, and

        - changes its state to Idle.

      In response to a ConnectRetryTimer_Expires event (Event 9), the
      local system:

        - restarts the ConnectRetryTimer (with initial value),

        - initiates a TCP connection to the other BGP peer,

        - continues to listen for a TCP connection that may be initiated
          by a remote BGP peer, and

        - changes its state to Connect.

      If the local system receives a DelayOpenTimer_Expires event (Event
      12), the local system:

        - sets the ConnectRetryTimer to zero,

        - stops and clears the DelayOpenTimer (set to zero),

        - completes the BGP initialization,

        - sends the OPEN message to its remote peer,

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        - sets its hold timer to a large value, and

        - changes its state to OpenSent.

      A HoldTimer value of 4 minutes is also suggested for this state
      transition.

      If the local system receives a TcpConnection_Valid event (Event
      14), the local system processes the TCP connection flags and stays
      in the Active state.

      If the local system receives a Tcp_CR_Invalid event (Event 15),
      the local system rejects the TCP connection and stays in the
      Active State.

      In response to the success of a TCP connection (Event 16 or Event
      17), the local system checks the DelayOpen optional attribute
      prior to processing.

        If the DelayOpen attribute is set to TRUE, the local system:

          - stops the ConnectRetryTimer and sets the ConnectRetryTimer
            to zero,

          - sets the DelayOpenTimer to the initial value
            (DelayOpenTime), and

          - stays in the Active state.

        If the DelayOpen attribute is set to FALSE, the local system:

          - sets the ConnectRetryTimer to zero,

          - completes the BGP initialization,

          - sends the OPEN message to its peer,

          - sets its HoldTimer to a large value, and

          - changes its state to OpenSent.

      A HoldTimer value of 4 minutes is suggested as a "large value" for
      the HoldTimer.

      If the local system receives a TcpConnectionFails event (Event
      18), the local system:

        - restarts the ConnectRetryTimer (with the initial value),

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        - stops and clears the DelayOpenTimer (sets the value to zero),

        - releases all BGP resource,

        - increments the ConnectRetryCounter by 1,

        - optionally performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

      If an OPEN message is received and the DelayOpenTimer is running
      (Event 20), the local system:

        - stops the ConnectRetryTimer (if running) and sets the
          ConnectRetryTimer to zero,

        - stops and clears the DelayOpenTimer (sets to zero),

        - completes the BGP initialization,

        - sends an OPEN message,

        - sends a KEEPALIVE message,

        - if the HoldTimer value is non-zero,

            - starts the KeepaliveTimer to initial value,

            - resets the HoldTimer to the negotiated value,

          else if the HoldTimer is zero

            - resets the KeepaliveTimer (set to zero),

            - resets the HoldTimer to zero, and

        - changes its state to OpenConfirm.

      If the value of the autonomous system field is the same as the
      local Autonomous System number, set the connection status to an
      internal connection; otherwise it will be external.

      If BGP message header checking (Event 21) or OPEN message checking
      detects an error (Event 22) (see Section 6.2), the local system:

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        - (optionally) sends a NOTIFICATION message with the appropriate
          error code if the SendNOTIFICATIONwithoutOPEN attribute is set
          to TRUE,

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

      If a NOTIFICATION message is received with a version error (Event
      24), the local system checks the DelayOpenTimer.  If the
      DelayOpenTimer is running, the local system:

        - stops the ConnectRetryTimer (if running) and sets the
          ConnectRetryTimer to zero,

        - stops and resets the DelayOpenTimer (sets to zero),

        - releases all BGP resources,

        - drops the TCP connection, and

        - changes its state to Idle.

      If the DelayOpenTimer is not running, the local system:

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

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      In response to any other event (Events 8, 10-11, 13, 19, 23,
      25-28), the local system:

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by one,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

   OpenSent:

      In this state, BGP FSM waits for an OPEN message from its peer.

      The start events (Events 1, 3-7) are ignored in the OpenSent
      state.

      If a ManualStop event (Event 2) is issued in the OpenSent state,
      the local system:

        - sends the NOTIFICATION with a Cease,

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection,

        - sets the ConnectRetryCounter to zero, and

        - changes its state to Idle.

      If an AutomaticStop event (Event 8) is issued in the OpenSent
      state, the local system:

        - sends the NOTIFICATION with a Cease,

        - sets the ConnectRetryTimer to zero,

        - releases all the BGP resources,

        - drops the TCP connection,

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        - increments the ConnectRetryCounter by 1,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

      If the HoldTimer_Expires (Event 10), the local system:

        - sends a NOTIFICATION message with the error code Hold Timer
          Expired,

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

      If a TcpConnection_Valid (Event 14), Tcp_CR_Acked (Event 16), or a
      TcpConnectionConfirmed event (Event 17) is received, a second TCP
      connection may be in progress.  This second TCP connection is
      tracked per Connection Collision processing (Section 6.8) until an
      OPEN message is received.

      A TCP Connection Request for an Invalid port (Tcp_CR_Invalid
      (Event 15)) is ignored.

      If a TcpConnectionFails event (Event 18) is received, the local
      system:

        - closes the BGP connection,

        - restarts the ConnectRetryTimer,

        - continues to listen for a connection that may be initiated by
          the remote BGP peer, and

        - changes its state to Active.

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      When an OPEN message is received, all fields are checked for
      correctness.  If there are no errors in the OPEN message (Event
      19), the local system:

        - resets the DelayOpenTimer to zero,

        - sets the BGP ConnectRetryTimer to zero,

        - sends a KEEPALIVE message, and

        - sets a KeepaliveTimer (via the text below)

        - sets the HoldTimer according to the negotiated value (see
          Section 4.2),

        - changes its state to OpenConfirm.

      If the negotiated hold time value is zero, then the HoldTimer and
      KeepaliveTimer are not started.  If the value of the Autonomous
      System field is the same as the local Autonomous System number,
      then the connection is an "internal" connection; otherwise, it is
      an "external" connection.  (This will impact UPDATE processing as
      described below.)

      If the BGP message header checking (Event 21) or OPEN message
      checking detects an error (Event 22)(see Section 6.2), the local
      system:

        - sends a NOTIFICATION message with the appropriate error code,

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is TRUE, and

        - changes its state to Idle.

      Collision detection mechanisms (Section 6.8) need to be applied
      when a valid BGP OPEN message is received (Event 19 or Event 20).
      Please refer to Section 6.8 for the details of the comparison.  A

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      CollisionDetectDump event occurs when the BGP implementation
      determines, by means outside the scope of this document, that a
      connection collision has occurred.

      If a connection in the OpenSent state is determined to be the
      connection that must be closed, an OpenCollisionDump (Event 23) is
      signaled to the state machine.  If such an event is received in
      the OpenSent state, the local system:

        - sends a NOTIFICATION with a Cease,

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

      If a NOTIFICATION message is received with a version error (Event
      24), the local system:

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection, and

        - changes its state to Idle.

      In response to any other event (Events 9, 11-13, 20, 25-28), the
      local system:

        - sends the NOTIFICATION with the Error Code Finite State
          Machine Error,

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

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        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

   OpenConfirm State:

      In this state, BGP waits for a KEEPALIVE or NOTIFICATION message.

      Any start event (Events 1, 3-7) is ignored in the OpenConfirm
      state.

      In response to a ManualStop event (Event 2) initiated by the
      operator, the local system:

        - sends the NOTIFICATION message with a Cease,

        - releases all BGP resources,

        - drops the TCP connection,

        - sets the ConnectRetryCounter to zero,

        - sets the ConnectRetryTimer to zero, and

        - changes its state to Idle.

      In response to the AutomaticStop event initiated by the system
      (Event 8), the local system:

        - sends the NOTIFICATION message with a Cease,

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

      If the HoldTimer_Expires event (Event 10) occurs before a
      KEEPALIVE message is received, the local system:

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        - sends the NOTIFICATION message with the Error Code Hold Timer
          Expired,

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

      If the local system receives a KeepaliveTimer_Expires event (Event
      11), the local system:

        - sends a KEEPALIVE message,

        - restarts the KeepaliveTimer, and

        - remains in the OpenConfirmed state.

      In the event of a TcpConnection_Valid event (Event 14), or the
      success of a TCP connection (Event 16 or Event 17) while in
      OpenConfirm, the local system needs to track the second
      connection.

      If a TCP connection is attempted with an invalid port (Event 15),
      the local system will ignore the second connection attempt.

      If the local system receives a TcpConnectionFails event (Event 18)
      from the underlying TCP or a NOTIFICATION message (Event 25), the
      local system:

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

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        - changes its state to Idle.

      If the local system receives a NOTIFICATION message with a version
      error (NotifMsgVerErr (Event 24)), the local system:

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection, and

        - changes its state to Idle.

      If the local system receives a valid OPEN message (BGPOpen (Event
      19)), the collision detect function is processed per Section 6.8.
      If this connection is to be dropped due to connection collision,
      the local system:

        - sends a NOTIFICATION with a Cease,

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection (send TCP FIN),

        - increments the ConnectRetryCounter by 1,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

      If an OPEN message is received, all fields are checked for
      correctness.  If the BGP message header checking (BGPHeaderErr
      (Event 21)) or OPEN message checking detects an error (see Section
      6.2) (BGPOpenMsgErr (Event 22)), the local system:

        - sends a NOTIFICATION message with the appropriate error code,

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

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        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

      If, during the processing of another OPEN message, the BGP
      implementation determines, by a means outside the scope of this
      document, that a connection collision has occurred and this
      connection is to be closed, the local system will issue an
      OpenCollisionDump event (Event 23).  When the local system
      receives an OpenCollisionDump event (Event 23), the local system:

        - sends a NOTIFICATION with a Cease,

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

      If the local system receives a KEEPALIVE message (KeepAliveMsg
      (Event 26)), the local system:

        - restarts the HoldTimer and

        - changes its state to Established.

      In response to any other event (Events 9, 12-13, 20, 27-28), the
      local system:

        - sends a NOTIFICATION with a code of Finite State Machine
          Error,

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

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        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

   Established State:

      In the Established state, the BGP FSM can exchange UPDATE,
      NOTIFICATION, and KEEPALIVE messages with its peer.

      Any Start event (Events 1, 3-7) is ignored in the Established
      state.

      In response to a ManualStop event (initiated by an operator)
      (Event 2), the local system:

        - sends the NOTIFICATION message with a Cease,

        - sets the ConnectRetryTimer to zero,

        - deletes all routes associated with this connection,

        - releases BGP resources,

        - drops the TCP connection,

        - sets the ConnectRetryCounter to zero, and

         - changes its state to Idle.

      In response to an AutomaticStop event (Event 8), the local system:

        - sends a NOTIFICATION with a Cease,

        - sets the ConnectRetryTimer to zero

        - deletes all routes associated with this connection,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

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      One reason for an AutomaticStop event is: A BGP receives an UPDATE
      messages with a number of prefixes for a given peer such that the
      total prefixes received exceeds the maximum number of prefixes
      configured.  The local system automatically disconnects the peer.

      If the HoldTimer_Expires event occurs (Event 10), the local
      system:

        - sends a NOTIFICATION message with the Error Code Hold Timer
          Expired,

        - sets the ConnectRetryTimer to zero,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

      If the KeepaliveTimer_Expires event occurs (Event 11), the local
      system:

        - sends a KEEPALIVE message, and

        - restarts its KeepaliveTimer, unless the negotiated HoldTime
          value is zero.

      Each time the local system sends a KEEPALIVE or UPDATE message, it
      restarts its KeepaliveTimer, unless the negotiated HoldTime value
      is zero.

      A TcpConnection_Valid (Event 14), received for a valid port, will
      cause the second connection to be tracked.

      An invalid TCP connection (Tcp_CR_Invalid event (Event 15)) will
      be ignored.

      In response to an indication that the TCP connection is
      successfully established (Event 16 or Event 17), the second
      connection SHALL be tracked until it sends an OPEN message.

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      If a valid OPEN message (BGPOpen (Event 19)) is received, and if
      the CollisionDetectEstablishedState optional attribute is TRUE,
      the OPEN message will be checked to see if it collides (Section
      6.8) with any other connection.  If the BGP implementation
      determines that this connection needs to be terminated, it will
      process an OpenCollisionDump event (Event 23).  If this connection
      needs to be terminated, the local system:

        - sends a NOTIFICATION with a Cease,

        - sets the ConnectRetryTimer to zero,

        - deletes all routes associated with this connection,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations is set to TRUE, and

        - changes its state to Idle.

      If the local system receives a NOTIFICATION message (Event 24 or
      Event 25) or a TcpConnectionFails (Event 18) from the underlying
      TCP, the local system:

        - sets the ConnectRetryTimer to zero,

        - deletes all routes associated with this connection,

        - releases all the BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

        - changes its state to Idle.

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      If the local system receives a KEEPALIVE message (Event 26), the
      local system:

        - restarts its HoldTimer, if the negotiated HoldTime value is
          non-zero, and

        - remains in the Established state.

      If the local system receives an UPDATE message (Event 27), the
      local system:

        - processes the message,

        - restarts its HoldTimer, if the negotiated HoldTime value is
          non-zero, and

        - remains in the Established state.

      If the local system receives an UPDATE message, and the UPDATE
      message error handling procedure (see Section 6.3) detects an
      error (Event 28), the local system:

        - sends a NOTIFICATION message with an Update error,

        - sets the ConnectRetryTimer to zero,

        - deletes all routes associated with this connection,

        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.

      In response to any other event (Events 9, 12-13, 20-22), the local
      system:

        - sends a NOTIFICATION message with the Error Code Finite State
          Machine Error,

        - deletes all routes associated with this connection,

        - sets the ConnectRetryTimer to zero,

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        - releases all BGP resources,

        - drops the TCP connection,

        - increments the ConnectRetryCounter by 1,

        - (optionally) performs peer oscillation damping if the
          DampPeerOscillations attribute is set to TRUE, and

        - changes its state to Idle.



(page 75 continued on part 4)

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