Compatibility Of Rstp With 802.1D - Dell PowerConnect B-RX Configuration Manual

13

Compatibility of RSTP with 802.1D

FIGURE 61
Compatibility of RSTP with 802.1D
RSTP-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 RSTP-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.
380
Completing the TCN propagation
Switch 1
Bridge priority = 1000
Port2
Port3
Port3
Port2
Port4
Switch 3
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.
Switch 2
Bridge priority = 200
Port7 Port8
Port5
Port2
Port3
Port4
Port3
Port4
Port5
Switch 4
Bridge priority = 400
Switch 5
Bridge priority = 60
Port2
Port3
Port3
Port4
Port5
Switch 6
Bridge priority = 900
BigIron RX Series Configuration Guide
53-1001986-01