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372 BigIron RX Series Configuration Guide
53-1001810-01
Convergence in a complex RSTP topology
13
For example, Port3/Switch 2 in Figure 59 , fails. Port4/Switch 3 becomes the new Root port.
Port4/Switch 3 sends an RST BPDU with a TCN to Port4/Switch 4. To propagate the topology
change, Port4/Switch 4 then starts a TCN timer on itself, on the bridge’s Root port, and on other
ports on that bridge with a Designated role. Then Port3/Switch 4 sends RST BPDU with the TCN to
Port4/Switch 2. (Note the new active Layer 2 path in
Figure 59 .)
FIGURE 59 Beginning of topology change notice
Switch 2 then starts the TCN timer on the Designated ports and sends RST BPDUs that contain the
TCN as follows (
Figure 60 ):
•
Port5/Switch 2 sends the TCN to Port2/Switch 5
•
Port4/Switch 2 sends the TCN to Port4/Switch 6
Switch 1
Bridge priority = 1000
Switch 2
Bridge priority = 200
Switch 5
Bridge priority = 60
Switch 6
Bridge priority = 900
Switch 4
Bridge priority = 400
Switch 3
Bridge priority = 300
Port2 Port2
Port2
Port2
Port3
Port3
Port3
Port3
Port3
Port3
Port4
Port4
Port4
Port4
Port5
Port 5
Port5
Port7 Port8
Indicates the active Layer 2 path
Indicates direction of TCN