Dell PowerConnect B-RX BigIron RX Series Configuration Guide v02.8.00 - Page 444

13 State machines FIGURE 47 Addition of a new root bridge Switch 100 Port2 Port1 Designated port Switch 200 Port2 Port1 Root port Port3 Port4 Port2 Designated port Switch 60 Port4 Designated port Switch 300 Port2 Port3 Switch 400 The handshake that occurs between Switch 60 and Switch 100 follows the one described in the previous section ("Handshake when no root port is elected" on page 363). The former root bridge becomes a non-root bridge and establishes a Root port (Figure 48). However, since Switch 200 already had a Root port in a forwarding state, RSTP uses the Proposing -> Proposed -> Sync and Reroot -> Sync and Rerooted -> Rerooted and Synced -> Agreed handshake: • Proposing and Proposed - The Designated port on the new root bridge (Port4/Switch 60) sends an RST BPDU that contains a proposing signal to Port4/Switch 200 to inform the port that it is ready to put itself in a forwarding state (Figure 48). RSTP algorithm determines that the RST BPDU that Port4/Switch 200 received is superior to what it can generate, so Port4/Switch 200 assumes a Root port role. 368 BigIron RX Series Configuration Guide 53-1002253-01