Convergence in a complex 802.1w topology, Figure 81 – Brocade TurboIron 24X Series Configuration Guide User Manual

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Brocade TurboIron 24X Series Configuration Guide

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Configuring STP related features

Convergence in a complex 802.1W topology

The following is an example of a complex 802.1W topology.

FIGURE 81

Complex 802.1W topology

Figure 81

, Switch 5 is selected as the root bridge since it is the bridge with the highest priority.

Lines in the figure show the point-to-point connection to the bridges in the topology.

Switch 5 sends an RST BPDU that contains a proposal flag to Port5/Switch 2. When handshakes
are completed in Switch 5, Port5/Switch 2 is selected as the Root port on Switch 2. All other ports
on Switch 2 are given Designated port role with discarding states.

Port5/Switch 2 then sends an RST BPDU with an agreed flag to Switch 5 to confirm that it is the
new Root port and the port enters a forwarding state. Port7 and Port8 are informed of the identity
of the new Root port. 802.1W algorithm selects Port7 as the Designated port while Port8 becomes
the Backup port.

Port3/Switch 5 sends an RST BPDU to Port3/Switch 6 with a proposal flag. When Port3/Switch 5
receives the RST BPDU, handshake mechanisms select Port3 as the Root port of Switch 6. All
other ports are given a Designated port role with discarding states. Port3/Switch 6 then sends an
RST BPDU with an agreed flag to Port3/Switch 5 to confirm that it is the Root port. The Root port
then goes into a forwarding state.

Now, Port4/Switch 6 receives RST BPDUs that are superior to what it can transmit; therefore, it is
given the Alternate port role. The port remains in discarding state.

Port5/Switch 6 receives RST BPDUs that are inferior to what it can transmit. The port is then given
a Designated port role.

Bridge priority = 1000

Bridge priority = 200

Bridge priority = 300

Bridge priority = 400

Bridge priority = 60

Bridge priority = 900

Port3

Port4

Port5

Port4

Port2

Port7

Port5

Port8

Switch 1

Switch 3

Switch 4

Switch 2

Switch 5

Switch 6