HP ProCurve 9304M Installation And Configuration Manual page 249

previous Root port, enters a discarding state and negotiates with other ports on the bridge to establish its new role
and state, until it finally assumes the role of a Designated port.
Next, the following happens:
• Port3/Routing Switch 2, the Designated port, sends an RST BPDU, with a proposal flag to Port3/Routing
Switch 3.
• Port2/Routing Switch 2 also sends an RST BPDU with an agreed flag to Port2/Routing Switch 1 and then
places itself into a forwarding state.
When Port2/Routing Switch 1 receives the RST BPDU with an agreed flag sent by Port2/Routing Switch 2, it puts
that port into a forwarding state. The topology is now fully converged.
When Port3/Routing Switch 3 receives the RST BPDU that Port3/Routing Switch 2 sent, 802.1W algorithm
determines that these RST BPDUs are superior to those that Port3/Routing Switch 3 can transmit. Therefore,
Port3/Routing Switch 3 is given a new role, that of an Alternate port. Port3/Routing Switch 3 immediately enters a
discarding state.
Now Port3/Routing Switch 2 does not go into a forwarding state instantly like the Root port. It waits until the
forward delay timer expires twice on that port while it is still in a Designated role, before it can proceed to the
forwarding state. The wait, however, does not cause a denial of service, since the essential connectivity in the
topology has already been established.
When fully restored, the topology is the same as that shown on Figure 8.15.
Convergence in a Complex 802.1W Topology
The following is an example of a complex 802.1W topology.
Figure 8.18 Complex 802.1W Topology
Routing Switch 1
Bridge priority = 1000
Port3
Port2
Port3
Routing Switch 3
Bridge priority = 300
In Figure 8.18, Routing 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.
Configuring Spanning Tree Protocol (STP) and Advanced STP Features
Routing Switch 2
Bridge priority = 200
Port7
Port2 Port2
Port3
Port3
Port4 Port4
Routing Switch 4
Bridge priority = 400
Routing
Port8
Bridge priority = 60
Port5
Port2
Port4
Port4
Port5 Port5
Bridge priority = 900
Switch 5
Port3
Port3
Routing Switch 6
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