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ENARSI > 11. BGP Message and FSM > Flashcards

11. BGP Message and FSM Flashcards

1
Q

What are the BGP message types?

A
  • Open
  • Keepalive
  • Update
  • Route Refresh
  • Notification
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2
Q

What is special about the route refresh message?

A

The route refresh message is when a soft reset occurs

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3
Q

What does setting the KEEPALIVE interval to 0 represent?

A

Keepalives are never sent

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4
Q

What is the default keepalive interval for BGP?

A

60 seconds

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5
Q

In which BGP message type would you find the NLRI and path attributes?

A

UPDATE

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6
Q

What are the stages FSM of BGP?

A
  • Idle
  • Connect
  • Active
  • OpenSent
  • OpenConfirm
  • Established
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7
Q

What happens in the Idle stage?

A

BGP detects a start event, tries to initiate a TCP connection, and listens for a new connection from another peer

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8
Q

What happens if an error causes BGP to go back to the Idle state for the second time?

A

The ConnectRetry timers is set to 60 seconds and must decrement to 0 before a new connection can be initiated. Further errors wil double the timer in legnth of the previous one

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9
Q

What happens in the Connect stage?

A

BGP initiates the connection. If the three-way handshake completes, the ConnectRetry timer resets, an OPEN message will be send to the neighbor. The status will be changed to OpenSent

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10
Q

What happens if the ConnectRetry timer depletes before the Connect stage has completed?

A

A new TCP connection is attempted, the ConnectRetry timer is reset and the state is set to Active. The neighbor with the higher IP manages the connection

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11
Q

What happens in the Active stage?

A

BGP start a new three-way handshake,. If succesful an OPEN message is send, the hold timer placed 4 minutes and the status changed to OpenSent.

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12
Q

What happens if the connection attempt fails in the Active state?

A

The state moves back to Connect and the ConnectRetry timer is reset

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13
Q

What happens in the OpenSent stage?

A

The router will wait for an open message and will compare:

  • BGP version
  • Source IP
  • AS
  • RID
  • Security parameters

The hold timer is negotiated (lower wins) and a KEEPALIVE is send (if not set to 0). The state if moved to OpenConfirm

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14
Q

What happens when an error is found in the OPEN message during the OpenSent stage?

A

A notification message is sent, and the state is moved back to Idle

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15
Q

What happens when TCP receives a disconnect message in the OpenSent state?

A

BGP closes the connection and goes back to Active

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16
Q

What happens in the OpenConfirm stage?

A

BGP waits for a KEEPALIVE of NOTIFICATION. If a KEEPALIVE is received the state will move to established. With NOTIFICATION back to idle

17
Q

What happens in the Established stage?

A

Routes will be exchanged with UPDATE messages.

ENARSI (25 decks)

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