Dell Brocade DCX, Configuration Manual

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BigIron RX Series Configuration Guide 363
53-1001810-01
Convergence in a simple topology
13
The Designated port on Switch 60 goes into a forwarding state once it receives the RST BPDU with
the agreed flag.
FIGURE 52 Handshake completed after election of new root port
Recall that Switch 200 sent the agreed flag to Port4/Switch 60 and not to Port1/Switch 100 (the
port that connects Switch 100 to Switch 200). Therefore, Port1/Switch 100 does not go into
forwarding state instantly. It waits until two instances of the forward delay timer expires on the port
before it goes into forwarding state.
At this point the handshake between the Switch 60 and Switch 200 is complete.
The remaining bridges (Switch 300 and Switch 400) may have to go through the reroot handshake
if a new Root port needs to be assigned.
Convergence in a simple topology
The examples in this section illustrate how RSTP convergence occurs in a simple Layer 2 topology
at start-up.
NOTE
The remaining examples assume that the appropriate handshake mechanisms occur as port roles
and states change.
Switch 100
Port2
Designated
port
Port2
Root port
Switch 60
Port4
Designated port
Port1
Proposing
Port1
Alternate port
Port4
Root port
Switch 200
Port2
Port2
Port3
Port3
Proposing Proposing
Switch 300
Switch 400