144 | Bidirectional Forwarding Detection (BFD)w w w . d e l l . c o m | s u p p o r t . d e l l . c o m 4. The passive system receives the control packet, changes its state to Up. Both systems agree that asession has been established. However, since both members must send a control packet—that requiresa response—anytime there is a state change or change in a session parameter, the passive system sendsa final response indicating the state change. After this, periodic control packets are exchanged.Session state changesThe illustration below shows how the session state on a system changes based on the status notification itreceives from the remote system. For example, if a session on a system is down, and it receives a Downstatus notification from the remote system, the session state on the local system changes to Init.ACTIVE System PASSIVE SystemSteady Rate of Control PacketsVersion: 1Diag Code: 0 (assumes no previous session)State: DownFlag: P:1Detect Multiplier: User-configurableMy Discriminator: X ( Active System Session ID)Your Discriminator: 0Desired Min TX Interval: User-configurableRequired Min RX Interval: User-configurableRequired Min Echo RX Interval: User-configurableInit State ChangeVersion: 1Diag Code: 0 (assumes no previous session)State: InitFlag: F: 1Detect Multiplier: User-configurableMy Discriminator: Y (Passsive System Session ID)Your Discriminator: XDesired Min TX Interval: User-configurableRequired Min RX Interval: User-configurableRequired Min Echo RX Interval: User-configurableTransmit Interval: User-configurableUp State ChangeVersion: 1Diag Code: 0 (assumes no previous session)State: UpFlag: P: 1Detect Multiplier: User-configurableMy Discriminator: XYour Discriminator: YDesired Min TX Interval: User-configurableRequired Min RX Interval: User-configurableRequired Min Echo RX Interval: User-configurableVersion: 1Diag Code: 0 (assumes no previous session)State: UpFlag: F: 1Detect Multiplier: User-configurableMy Discriminator: YYour Discriminator: XDesired Min TX Interval: User-configurableRequired Min RX Interval: User-configurableRequired Min Echo RX Interval: User-configurableUp State ChangeDefault Session State: Down Default Session State: DownPeriodic Control PacketVersion: 1Diag Code: 0 (assumes no previous session)State: UpFlag: P: ClearDetect Multiplier: User-configurableMy Discriminator: XYour Discriminator: YDesired Min TX Interval: User-configurableRequired Min RX Interval: User-configurableRequired Min Echo RX Interval: User-configurable fnC0036mpDownInit UpUp, Admin Down, TimerInitDownAdmin Down,TimerAdmin Down,Down,TimerDownInit, UpUp, Initthe packet receivedcurrent session statefnC0037mp
