Dell PowerConnect FCS624S Configuration Guide - Page 280

8 Configuring STP related features FIGURE 32 Agree stage Switch 100 Root Bridge RST BPDU sent with an Agreed flag Port1 Designated port Forwarding Port1 Root port Synced Forwarding BigIron Switch 200 Port2 Synced Discarding Port3 Synced Discarding Port2 Switch 300 Port3 Switch 400 Indicates a signal At this point, the handshake mechanism is complete between Switch 100, the root bridge, and Switch 200. Switch 200 updates the information on the Switch 200 Designated ports (Port2 and Port3) and identifies the new root bridge. The Designated ports send RST BPDUs, containing proposal flags, to their downstream bridges, without waiting for the hello timers to expire on them. This process starts the handshake with the downstream bridges. For example, Port2/Switch 200 sends an RST BPDU to Port2/Switch 300 that contains a proposal flag. Port2/Switch 300 asserts a proposed signal. Ports in Switch 300 then set sync signals on the ports to synchronize and negotiate their roles and states. Then the ports assert a synced signal and when the Root port in Switch 300 asserts its synced signal, it sends an RST BPDU to Switch 200 with an agreed flag. This handshake is repeated between Switch 200 and Switch 400 until all Designated and Root ports are in forwarding states. Handshake when a root port has been elected If a non-root bridge already has a Root port, 802.1W uses a different type of handshake. For example, in Figure 33, a new root bridge is added to the topology. 238 PowerConnect B-Series FCX Configuration Guide 53-1002266-01