ZyXEL Communications ES-2048 - Manual (Page 59)

ES-2000 Series Switch Support Notes
All contents copyright (c) 2006 ZyXEL Communications Corporation.
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1. Switch A bridge ID = 8000:00A0:C511:1111, Switch B bridge ID =
8000:00A0:C522:2222, Switch C bridge ID =
0001:00A0:C533:3333. Switch C has the lowest bridge ID, so
Switch C is the root bridge. All ports of the root bridge are
designated ports, so Port 1 is designated port.
2. For non-root bridge Switch A, Port 1 path cost to root bridge is 19,
Port 2 path cost is 119, 100 (Switch A Port 2) + 19 (Switch B Port 1).
For Switch B, Port 1 path cost is 19, Port 2 path cost is 119. Root
port = Port 1 of Switch A and Switch B because it has the lowest
path cost to the root bridge Switch C.
3. On Segment A, both Port 2 of Switch A and Switch B have the
same path cost to root bridge. Since Switch A has lower bridge ID
than Switch B, the designated port is selected on Switch A. So Port
2 of Switch A is designated port.
Blocking = Port 2 of Switch B, the non designated port on the segment.
Forwarding = All designated ports and root ports.