Dell PowerConnect B-FCXs Configuration Manual page 272

8
Configuring STP related features
FIGURE 26
Ports on Switch 1
All ports on Switch 1, the root bridge, are assigned Designated port roles.
Ports on Switch 2
Port2 on Switch 2 directly connects to the root bridge; therefore, Port2 is the Root port.
The bridge priority value on Switch 2 is superior to that of Switch 3 and Switch 4; therefore, the
ports on Switch 2 that connect to Switch 3 and Switch 4 are given the Designated port role.
Furthermore, Port7 and Port8 on Switch 2 are physically connected. The RST BPDUs transmitted
by Port7 are superior to those Port8 transmits. Therefore, Port8 is the Backup port and Port7 is the
Designated port.
Ports on Switch 3
Port2 on Switch 3 directly connects to the Designated port on the root bridge; therefore, it assumes
the Root port role.
The root path cost of the RST BPDUs received on Port4/Switch 3 is inferior to the RST BPDUs
transmitted by the port; therefore, Port4/Switch 3 becomes the Designated port.
Similarly Switch 3 has a bridge priority value inferior to Switch 2. Port3 on Switch 3 connects to Port
3 on Switch 2. This port will be given the Alternate port role, since a Root port is already established
on this bridge.
Ports Switch 4
Switch 4 is not directly connected to the root bridge. It has two ports with superior incoming RST
BPDUs from two separate LANs: Port3 and Port4. The RST BPDUs received on Port3 are superior to
the RST BPDUs received on port 4; therefore, Port3 becomes the Root port and Port4 becomes the
Alternate port.
230
Simple 802.1W topology
Switch 1
Port2
Bridge priority = 100
Port3
Port2
Port3
Switch 3
Port4
Bridge priority = 300
Port7 Port8
Switch 2
Port2
Bridge priority = 200
Port4
Port3
Port3
Switch 4
Port4
Bridge priority = 400
PowerConnect B-Series FCX Configuration Guide
53-1002266-01