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FTOS Configuration Guide for the C-Series - Force10 Networks

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3. The active system receives <strong>the</strong> response from <strong>the</strong> passive system, and changes its session state to Up. It<br />

<strong>the</strong>n sends a control packet indicating this state change. This is <strong>the</strong> third and final part of of <strong>the</strong><br />

handshake. At this point, <strong>the</strong> discriminator values have been exchanged, and <strong>the</strong> transmit intervals<br />

have been negotiated.<br />

4. The passive system receives <strong>the</strong> control packet, changes its state to Up. Both systems agree that a<br />

session has been established. However, since both members must send a control packet—that requires<br />

a response—anytime <strong>the</strong>re is a state change or change in a session parameter, <strong>the</strong> passive system sends<br />

a final response indicating <strong>the</strong> state change. After this, periodic control packets are exchanged.<br />

Figure 420 BFD Three-way Handshake<br />

Version: 1<br />

Diag Code: 0 (assumes no previous session)<br />

State: Up<br />

Flag: P: 1<br />

Detect Multiplier: User-configurable<br />

My Discriminator: X<br />

Your Discriminator: Y<br />

Desired Min TX Interval: User-configurable<br />

Required Min RX Interval: User-configurable<br />

Required Min Echo RX Interval: User-configurable<br />

Version: 1<br />

Diag Code: 0 (assumes no previous session)<br />

State: Up<br />

Flag: P: Clear<br />

Detect Multiplier: User-configurable<br />

My Discriminator: X<br />

Your Discriminator: Y<br />

Desired Min TX Interval: User-configurable<br />

Required Min RX Interval: User-configurable<br />

Required Min Echo RX Interval: User-configurable<br />

Default Session State: Down<br />

ACTIVE System Flag: P:1<br />

PASSIVE System<br />

Session state changes<br />

Version: 1<br />

Diag Code: 0 (assumes no previous session)<br />

State: Down<br />

Detect Multiplier: User-configurable<br />

My Discriminator: X ( Active System Session ID)<br />

Your Discriminator: 0<br />

Desired Min TX Interval: User-configurable<br />

Required Min RX Interval: User-configurable<br />

Required Min Echo RX Interval: User-configurable<br />

Steady Rate of Control Packets<br />

Init State Change<br />

Up State Change<br />

Up State Change<br />

Periodic Control Packet<br />

Default Session State: Down<br />

Transmit Interval: User-configurable<br />

Version: 1<br />

Diag Code: 0 (assumes no previous session)<br />

State: Init<br />

Flag: F: 1<br />

Detect Multiplier: User-configurable<br />

My Discriminator: Y (Passsive System Session ID)<br />

Your Discriminator: X<br />

Desired Min TX Interval: User-configurable<br />

Required Min RX Interval: User-configurable<br />

Required Min Echo RX Interval: User-configurable<br />

Version: 1<br />

Diag Code: 0 (assumes no previous session)<br />

State: Up<br />

Flag: F: 1<br />

Detect Multiplier: User-configurable<br />

My Discriminator: Y<br />

Your Discriminator: X<br />

Desired Min TX Interval: User-configurable<br />

Required Min RX Interval: User-configurable<br />

Required Min Echo RX Interval: User-configurable<br />

fnC0036mp<br />

Figure 421 shows how <strong>the</strong> session state on a system changes based on <strong>the</strong> status notification it receives<br />

from <strong>the</strong> remote system. For example, if a session on a system is down, and it receives a Down status<br />

notification from <strong>the</strong> remote system, <strong>the</strong> session state on <strong>the</strong> local system changes to Init.<br />

602 Bidirectional Forwarding Detection

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