Brocade FastIron Ethernet Switch Platform and Layer 2 Switching Configuration Guide - Manual (Page 289)

Convergence at start up
In the following figure, two bridges Switch 2 and Switch 3 are powered up. There are point-to-point
connections between Port3/Switch 2 and Port3/Switch 3.
FIGURE 53 Convergence between two bridges
At power up, all ports on Switch 2 and Switch 3 assume Designated port roles and are at discarding
states before they receive any RST BPDU.
Port3/Switch 2, with a Designated role, transmits an RST BPDU with a proposal flag to Port3/Switch 3.
A ports with a Designated role sends the proposal flag in its RST BPDU when they are ready to move to
a forwarding state.
Port3/Switch 3, which starts with a role of Designated port, receives the RST BPDU and finds that it is
superior to what it can transmit; therefore, Port3/Switch 3 assumes a new port role, that of a Root port.
Port3/Switch 3 transmits an RST BPDU with an agreed flag back to Switch 2 and immediately goes into
a forwarding state.
Port3/Switch 2 receives the RST BPDU from Port3/Switch 3 and immediately goes into a forwarding
state.
Now 802.1W has fully converged between the two bridges, with Port3/Switch 3 as an operational root
port in forwarding state and Port3/Switch 2 as an operational Designated port in forwarding state.
Next, Switch 1 is powered up. See the following figure.
Spanning Tree Protocol
FastIron Ethernet Switch Platform and Layer 2 Switching Configuration Guide 289
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