Brocade FastIron Ethernet Switch Platform and Layer 2 Switching Configuration Guide - Manual (Page 283)

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 the following figure, a new root bridge is added to the topology.
FIGURE 47 Addition of a new root bridge
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 ). 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, 802.1W 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 ). 802.1W 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.
Spanning Tree Protocol
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