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14-11
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
OL-10101-02
Chapter 14 Configuring MSTP
Configuring MSTP Features
• 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 describe how to configure basic MSTP features:
• Default MSTP Configuration, page 14-11
• MSTP Configuration Guidelines, page 14-12
• Specifying the MST Region Configuration and Enabling MSTP, page 14-13 (required)
• Configuring the Root Switch, page 14-14 (optional)
• Configuring a Secondary Root Switch, page 14-15 (optional)
• Configuring the Port Priority, page 14-16 (optional)
• Configuring the Path Cost, page 14-17 (optional)
• Configuring the Switch Priority, page 14-18 (optional)
• Configuring the Hello Time, page 14-19 (optional)
• Configuring the Forwarding-Delay Time, page 14-20 (optional)
• Configuring the Maximum-Aging Time, page 14-20 (optional)
• Configuring the Maximum-Hop Count, page 14-21 (optional)
• Specifying the Link Type to Ensure Rapid Transitions, page 14-21 (optional)
• Restarting the Protocol Migration Process, page 14-22 (optional)
Default MSTP Configuration
Table 14-3 shows the default MSTP configuration.
Ta b l e 14-3 Default MSTP Configuration
Feature Default Setting
Spanning-tree mode PVST+ (Rapid PVST+ and MSTP are disabled).
Switch priority (configurable on a per-CIST interface basis) 32768.
Spanning-tree port priority (configurable on a per-CIST interface basis) 128.
Spanning-tree port cost (configurable on a per-CIST interface basis) 1000 Mbps: 4.
100 Mbps: 19
10 Mbps: 100.