Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 463)

Multi-Service IronWare Switching Configuration Guide 433
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Compatibility of RSTP with 802.1D
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Then FRY1, Switch 5, and Switch 6 send RST BPDUs that contain the TCN to Switch 3 and Switch 4
to complete the TCN propagation.
FIGURE 93 Completing the TCN propagation
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:
• 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.
Once a port operates in the 802.1D mode, 802.1D convergence times are used and rapid
convergence is not realized.