Administrator Guide
• All ports in virtual local area networks (VLANs) and all enabled interfaces in Layer 2 mode are automatically added to the
spanning tree topology at the time you enable the protocol.
• To add interfaces to the spanning tree topology after you enable STP, enable the port and congure it for Layer 2 using the
switchport command.
• The IEEE Standard 802.1D allows 8 bits for port ID and 8 bits for priority. The 8 bits for port ID provide port IDs for 256 ports.
Conguring Interfaces for Layer 2 Mode
All interfaces on all switches that participate in spanning tree must be in Layer 2 mode and enabled.
Figure 123. Example of Conguring Interfaces for Layer 2 Mode
To congure and enable the interfaces for Layer 2, use the following command.
1. If the interface has been assigned an IP address, remove it.
INTERFACE mode
no ip address
2. Place the interface in Layer 2 mode.
INTERFACE
switchport
3. Enable the interface.
Spanning Tree Protocol (STP)
785