Dell Force10 S4810P - Page 144

144 | Bidirectional Forwarding Detection (BFD)
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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.
Session state changes
The illustration below shows how the session state on a system changes based on the status notification it
receives 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.
ACTIVE System
PASSIVE System
Steady Rate of Control Packets
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
Init State Change
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-configurab
le
Transmit Interval: User-configurable
Up State Change
V
ersion: 1
D
iag Code: 0 (assumes no previous session)
S
tate: Up
F
lag: P: 1
D
etect Multiplier: User-configurable
M
y Discriminator: X
Y
our Discriminator: Y
D
esired Min TX Interval: User-configurable
R
equired Min RX Interval: User-configurable
R
equired 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-configurab
le
Up State Change
Default Session State: Down
Default Session State: Down
Periodic Control Packet
V
ersion: 1
D
iag Code: 0 (assumes no previous session)
S
tate: Up
F
lag: P: Clear
D
etect Multiplier: User-configurable
M
y Discriminator: X
Y
our Discriminator: Y
D
esired Min TX Interval: User-configurable
R
equired Min RX Interval: User-configurable
Required Min Echo RX Interval: User-configurable
fnC0036m
p
Down
Init
Up
Up, Admin Down, Timer
Init
Down
Admin Down,
Timer
Admin Down,
Down,
Timer
D
own
Init, Up
Up, I
nit
the packet received
current session state
fnC0037mp