Administrator Guide

Important Points to Remember
• STP is disabled by default.
• The Dell Networking OS supports only one spanning tree instance (0). For multiple instances, enable
the multiple spanning tree protocol (MSTP) or per-VLAN spanning tree plus (PVST+). You may only
enable one flavor of spanning tree at any one time.
• 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 configure 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.
Configuring Interfaces for Layer 2 Mode
All interfaces on all switches that participate in spanning tree must be in Layer 2 mode and enabled.
Figure 105. Example of Configuring Interfaces for Layer 2 Mode
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Spanning Tree Protocol (STP)