Open Sent State

In the OpenSent state, the BGP peer waits for an OPEN message from its peer. After an OPEN message has been received, it is checked for validity. At this time, all fields in the OPEN message are checked against the local BGP configuration. Any fields that do not match the expected values cause an OPEN message error to occur. At this time, the BGP peer also checks to verify that a connection collision has not occurred. If the message is valid, the peer sends a KEEPALIVE mess age to itn eeer, sets t he KEePALIV E timer, sews th e hold ti mer, and t ransitions to the OpenConfitm sta te. Table 7-14 s hows the OpenSent state behaviors and their descriptions.

Table 7-14. OpenSent State Behaviors

OpenSent: St ate Behavior


Igno res incou ing start even ts

Stag: even ts are only re cei ved and ack nowledged in the Idle state. Any start even ts received d uoing the Connect state are igno red.

Waits for O PEN uoessage fioiu peer

The BGP peeo remains in the OpunSmnt state un til the followidg occurs:

• A valid OPEN message is received.

• ATCF3 (disco nnect event occuss.

f Ah NOTIF ICATION messa ge i s receivsd.

• The hold timer expires.

• Any other undefined event occurs.

A number of events can cause a BGP speaker to transition from the OpenSent state to the Idle state. As mentioned previously, if the speaker receives an invalid OPEN message from its peer, an OPEN message error will occur. Upon an OPEN message error, the local router sends out a NOTIFICATION message specifying the cause of the error and transitions to the Idle state where the connection process starts again. If a NOTIFICATION message is received from another peer router, the local router closes its TCP connection, resets the ConnectR^^ timer, and transitions to the Active state.

Upon receipt of a BGP stop event, hold-timer expiration, or other unexpected event, the local router also sends a NOTIFICATION message and transitions back to the Idle state. From the Idle state, the peering BGP routers once again try to launch a successful BGP session. Figure 7-19 shows the various events that might occur in the OpenSent state.

Figure 7-19. BGP OpenSent State

Figure 7-19. BGP OpenSent State

BGP pee rs rarely appear to wait in the OpenSent s tate for long amounts of time. After th e lo cal router receives an O pen mess age frem its pee r, it sends its eeer a KEEPALIVE me ssage and transitions to tne OhenConor m state.

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