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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
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Chapter 15 Configuring MSTP
Configuring MSTP Features
• Propagation—When an RSTP switch receives a TC message from another switch through a
designated or root port, it propagates the change to all of its nonedge, designated ports and to the
root port (excluding the port on which it is received). The switch starts the TC-while timer for all
such ports and flushes the information learned on them.
• Protocol migration—For backward compatibility with IEEE 802.1D switches, RSTP selectively
sends IEEE 802.1D configuration BPDUs and TCN BPDUs on a per-port basis.
When a port is initialized, the migrate-delay timer is started (specifies the minimum time during
which RSTP BPDUs are sent), and RSTP BPDUs are sent. While this timer is active, the switch
processes all BPDUs received on that port and ignores the protocol type.
If the switch receives an IEEE 802.1D BPDU after the port’s migration-delay timer has expired, it
assumes that it is connected to an IEEE 802.1D switch and starts using only IEEE 802.1D BPDUs.
However, if the RSTP switch is using IEEE 802.1D BPDUs on a port and receives an RSTP BPDU
after the timer has expired, it restarts the timer and starts using RSTP BPDUs on that port.
Configuring MSTP Features
These sections contain this configuration information:
• Default MSTP Configuration, page 15-12
• MSTP Configuration Guidelines, page 15-12
• Specifying the MST Region Configuration and Enabling MSTP, page 15-13 (required)
• Configuring the Root Switch, page 15-14 (optional)
• Configuring a Secondary Root Switch, page 15-16 (optional)
• Configuring Port Priority, page 15-17 (optional)
• Configuring Path Cost, page 15-18 (optional)
• Configuring the Switch Priority, page 15-19 (optional)
• Configuring the Hello Time, page 15-19 (optional)
• Configuring the Forwarding-Delay Time, page 15-20 (optional)
• Configuring the Maximum-Aging Time, page 15-21 (optional)
• Configuring the Maximum-Hop Count, page 15-21 (optional)
• Specifying the Link Type to Ensure Rapid Transitions, page 15-22 (optional)
• Restarting the Protocol Migration Process, page 15-22 (optional)