HP ProCurve 9304M Installation And Configuration Manual page 246

Installation and Basic Configuration Guide
Next, Routing Switch 1 is powered up (Figure 8.15).
Figure 8.15 Simple Layer 2 Topology
Bridge priority = 1500
Bridge priority = 2000
The point-to-point connections between the three bridges are as follows:
• Port2/Routing Switch 1 and Port2/Routing Switch 2
• Port4/Routing Switch 1 and Port4/Routing Switch 3
• Port3/Routing Switch 2 and Port3/Routing Switch 3
Ports 3 and 5 on Routing Switch 1 are physically connected together.
At start up, the ports on Routing Switch 1 assume Designated port roles, which are in discarding state. They begin
sending RST BPDUs with proposal flags to move into a forwarding state.
When Port4/Routing Switch 3 receives these RST BPDUs 802.1W algorithm determines that they are better than
the RST BPDUs that were previously received on Port3/Routing Switch 3. Port4/Routing Switch 3 is now selected
as Root port. This new assignment signals Port3/Routing Switch 3 to begin entering the discarding state and to
assume an Alternate port role. As it goes through the transition, Port3/Routing Switch 3 negotiates a new role and
state with its peer port, Port3/Routing Switch 2.
Port4/Routing Switch 3 sends an RST BPDU with an agreed flag to Port4/Routing Switch 1. Both ports go into
forwarding states.
Port2/Routing Switch 2 receives an RST BPDU. The 802.1W algorithm determines that these RST BPDUs that
are superior to any that any port on Routing Switch 2 can transmit; therefore, Port2/Routing Switch 2 assumes the
role of a Root port.
The new Root port then signals all ports on the bridge to start synchronization. Since none of the ports are Edge
ports, they all enter the discarding state and assume the role of Designated ports. Port3/Routing Switch 2, which
previously had a Designated role with a forwarding state, starts the discarding state. They also negotiate port roles
and states with their peer ports. Port3/Routing Switch 2 also sends an RST BPU to Port3/Routing Switch 3 with a
proposal flag to request permission go into a forwarding state.
The Port2/Routing Switch 2 bridge also sends an RST BPDU with an agreed flag Port2/Routing Switch 1 that
Port2 is the new Root port. Both ports go into forwarding states.
8 - 40
Routing Switch 2
Port2
Root port
Port3
Designated
port
Port3
Alternate
port
Port4
Root port
Routing Switch 3
Port3
Routing
Designated
Switch 1
port
Port2
Designated
port
Port4
Designated port
Port5
Backup port
Bridge priority = 1000