Brocade TurboIron 24X Series Configuration Guide - Manual (Page 578)

544 Brocade TurboIron 24X Series Configuration Guide
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Configuring STP related features
The Port2/Switch 2 bridge also sends an RST BPDU with an agreed flag Port2/Switch 1 that Port2
is the new Root port. Both ports go into forwarding states.
Now, Port3/Switch 3 is currently in a discarding state and is negotiating a port role. It received RST
BPDUs from Port3/Switch 2. The 802.1W algorithm determines that the RST BPDUs Port3/Switch
3 received are superior to those it can transmit; however, they are not superior to those that are
currently being received by the current Root port (Port4). Therefore, Port3 retains the role of
Alternate port.
Ports 3/Switch 1 and Port5/Switch 1 are physically connected. Port5/Switch 1 received RST
BPDUs that are superior to those received on Port3/Switch 1; therefore, Port5/Switch 1 is given
the Backup port role while Port3 is given the Designated port role. Port3/Switch 1, does not go
directly into a forwarding state. It waits until the forward delay time expires twice on that port before
it can proceed to the forwarding state.
Once convergence is achieved, the active Layer 2 forwarding path converges as shown in
Figure 79 .
FIGURE 79 Active Layer 2 path
Convergence after a link failure
What happens if a link in the 802.1W topology fails?
Switch 2
Port2
Root port
Port2
Designated
port
Port3
Designated
port
Switch 1
Port5
Backup port
Bridge priority = 1500 Bridge priority = 1000
Port4
Designated port
Port4
Root port
Port3
Designated
port
Port3
Alternate
port
Bridge priority = 2000
Switch 3
Indicates the active Layer 2 path