21-14
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-21521-01
Chapter 21 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 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 21-14
• MSTP Configuration Guidelines, page 21-15
• Specifying the MST Region Configuration and Enabling MSTP, page 21-16 (required)
• Configuring the Root Switch, page 21-18 (optional)
• Configuring a Secondary Root Switch, page 21-19 (optional)
• Configuring Port Priority, page 21-20 (optional)
• Configuring Path Cost, page 21-21 (optional)
• Configuring the Switch Priority, page 21-22 (optional)
• Configuring the Hello Time, page 21-23 (optional)
• Configuring the Forwarding-Delay Time, page 21-24 (optional)
• Configuring the Maximum-Aging Time, page 21-24 (optional)
• Configuring the Maximum-Hop Count, page 21-25 (optional)
• Specifying the Link Type to Ensure Rapid Transitions, page 21-25 (optional)
• Designating the Neighbor Type, page 21-26 (optional)
• Restarting the Protocol Migration Process, page 21-26 (optional)

Default MSTP Configuration

Table 21-4 shows the default MSTP configuration.
Tab le 21-4 Default MSTP Configuration
Feature Default Setting
Spanning-tree mode PVST+ (Rapid PVST+ and MSTP are disabled).
Switch priority (configurable on a per-CIST port basis) 32768.