Dell BigIron RX Series, Configuration Manual

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368 BigIron RX Series Configuration Guide
53-1002253-01
State machines
13
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” 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.
Switch 100
Port2
Designated
port
Switch 60
Port4
Designated port
Port2
Port1
Root port
Port4
Port3
Port2
Switch 200
Port2
Port3
Switch 300
Switch 400
Port1
Designated port