Brocade FastIron Ethernet Switch Platform and Layer 2 Switching Configuration Guide - Manual (Page 294)

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.
Next Switch 2 sends RST BPDUs with a proposal flag to Port3/Switch 4. Port3 becomes the Root port
for the bridge; all other ports are given a Designated port role with discarding states. Port3/Switch 4
sends an RST BPDU with an agreed flag to Switch 2 to confirm that it is the new Root port. The port
then goes into a forwarding state.
Now Port4/Switch 4 receives an RST BPDU that is superior to what it can transmit. The port is then
given an Alternate port role, and remains in discarding state.
Likewise, Port5/Switch 4 receives an RST BPDU that is superior to what it can transmit. The port is
also given an Alternate port role, and remains in discarding state.
Port2/Switch 2 transmits an RST BPDU with a proposal flag to Port2/Switch 1. Port2/Switch 1
becomes the Root port. All other ports on Switch 1 are given Designated port roles with discarding
states.
Port2/Switch 1 sends an RST BPDU with an agreed flag to Port2/Switch 2 and Port2/Switch 1 goes
into a forwarding state.
Port3/Switch 1 receives an RST BPDUs that is inferior to what it can transmit; therefore, the port
retains its Designated port role and goes into forwarding state only after the forward delay timer
expires twice on that port while it is still in a Designated role.
Port3/Switch 2 sends an RST BPDU to Port3/Switch 3 that contains a proposal flag. Port3/Switch 3
becomes the Root port, while all other ports on Switch 3 are given Designated port roles and go into
discarding states. Port3/Switch 3 sends an RST BPDU with an agreed flag to Port3/Switch 2 and
Port3/Switch 3 goes into a forwarding state.
Now, Port2/Switch 3 receives an RST BPDUs that is superior to what it can transmit so that port is
given an Alternate port state.
Port4/Switch 3 receives an RST BPDU that is inferior to what it can transmit; therefore, the port retains
its Designated port role.
Ports on all the bridges in the topology with Designated port roles that received RST BPDUs with
agreed flags go into forwarding states instantly. However, Designated ports that did not receive RST
BPDUs with agreed flags must wait until the forward delay timer expires twice on those port. Only then
will these port move into forwarding states.
The entire 802.1W topology converges in less than 300 msec and the essential connectivity is
established between the designated ports and their connected root ports.
After convergence is complete, the following figure shows the active Layer 2 path of the topology in
Figure 57 .
Spanning Tree Protocol
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