PowerConnect B-Series FCX Configuration Guide 245
53-1002266-01
Configuring STP related features
8
FIGURE 39 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 (Figure 40).
Port3
Designated
port
Port3
Root port
Bridge priority = 1500
Bridge priority = 2000
Switch 2
Switch 3
