Dell Force10 C150 Configuration Manual page 174

handshake. At this point, the discriminator values have been exchanged, and the transmit intervals
have been negotiated.
4. The passive system receives the control packet, changes its state to Up. Both systems agree that a
session has been established. However, since both members must send a control packet—that requires
a response—anytime there is a state change or change in a session parameter, the passive system sends
a final response indicating the state change. After this, periodic control packets are exchanged.
Figure 9-2. BFD Three-way Handshake
ACTIVE System
Version: 1
Diag Code: 0 (assumes no previous session)
State: Up
Flag: P: 1
Detect Multiplier: User-configurable
My Discriminator: X
Your Discriminator: Y
Desired Min TX Interval: User-configurable
Required Min RX Interval: User-configurable
Required Min Echo RX Interval: User-configurable
Version: 1
Diag Code: 0 (assumes no previous session)
State: Up
Flag: P: Clear
Detect Multiplier: User-configurable
My Discriminator: X
Your Discriminator: Y
Desired Min TX Interval: User-configurable
Required Min RX Interval: User-configurable
Required Min Echo RX Interval: User-configurable
Session state changes
Figure 9-3
from the remote system. For example, if a session on a system is down, and it receives a Down status
notification from the remote system, the session state on the local system changes to Init.
174 | Bidirectional Forwarding Detection
Default Session State: Down
shows how the session state on a system changes based on the status notification it receives
Version: 1
Diag Code: 0 (assumes no previous session)
State: Down
Flag: P:1
Detect Multiplier: User-configurable
My Discriminator: X ( Active System Session ID)
Your Discriminator: 0
Desired Min TX Interval: User-configurable
Required Min RX Interval: User-configurable
Required Min Echo RX Interval: User-configurable
Steady Rate of Control Packets
Init State Change
Up State Change
Up State Change
Periodic Control Packet
Transmit Interval: User-configurable
Default Session State: Down
PASSIVE System
Version: 1
Diag Code: 0 (assumes no previous session)
State: Init
Flag: F: 1
Detect Multiplier: User-configurable
My Discriminator: Y (Passsive System Session ID)
Your Discriminator: X
Desired Min TX Interval: User-configurable
Required Min RX Interval: User-configurable
Required Min Echo RX Interval: User-configurable
Version: 1
Diag Code: 0 (assumes no previous session)
State: Up
Flag: F: 1
Detect Multiplier: User-configurable
My Discriminator: Y
Your Discriminator: X
Desired Min TX Interval: User-configurable
Required Min RX Interval: User-configurable
Required Min Echo RX Interval: User-configurable
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