Dell PowerConnect B-FCXs Configuration Manual page 297

FIGURE 47
Compatibility of 802.1W with 802.1D
802.1W-enabled bridges are backward compatible with IEEE 802.1D bridges. This compatibility is
managed on a per-port basis by the Port Migration state machine. However, intermixing the two
types of bridges in the network topology is not advisable if you want to take advantage of the rapid
convergence feature.
Compatibility with 802.1D means that an 802.1W-enabled port can send BPDUs in the STP or
802.1D format when one of the following events occur:
•
•
Once a port operates in the 802.1D mode, 802.1D convergence times are used and rapid
convergence is not realized.
For example, in
Switch 10 and Switch 30 begin sending BPDUs in STP format to allow them to operate
transparently with Switch 20.
PowerConnect B-Series FCX Configuration Guide
53-1002266-01
Completing the TCN propagation
Switch 1
Port2
Bridge priority = 1000
Port3
Port2 Port3
Switch 3
Port4
Bridge priority = 300
Indicates the active Layer 2 path
Indicates direction of TCN
The port receives a legacy BPDU. A legacy BPDU is an STP BPDU or a BPDU in an 802.1D
format. The port that receives the legacy BPDU automatically configures itself to behave like a
legacy port. It sends and receives legacy BPDUs only.
The entire bridge is configured to operate in an 802.1D mode when an administrator sets the
bridge parameter to zero at the CLI, forcing all ports on the bridge to send legacy BPDUs only.
Figure 48, Switch 10 and Switch 30 receive legacy BPDUs from Switch 20. Ports on
Configuring STP related features
Port7 Port8
Port5
Switch 2
Port2
Bridge priority = 200
Port3
Port4
Port3
Port4
Switch 4 Port5
Bridge priority = 400
8
Port2
Switch 5
Bridge priority = 60
Port3
Port3
Port4
Switch 6
Port5
Bridge priority = 900
255