Brocade FastIron Ethernet Switch Platform and Layer 2 Switching Configuration Guide - Manual (Page 282)

FIGURE 46 Agree stage
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.
Spanning Tree Protocol
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