Spanning Tree Protocol (STP) | 579
Configuring Interfaces for Layer 2 Mode
All interfaces on all switches that participate in STP must be in Layer 2 mode and enabled.
Figure 33-1.  Example of Configuring Interfaces for Layer 2 Mode
To configure the interfaces for Layer 2 and then enable them, follow these steps: 
Step Task Command Syntax Command Mode
1 If the interface has been assigned an IP address, 
remove it.
no ip address
INTERFACE
2 Place the interface in Layer 2 mode.
switchport
INTERFACE
3 Enable the interface.
no shutdown
INTERFACE