DELL N3000 User Manual

Configuring the Spanning Tree Protocol

The switch spanning tree configuration is global in nature. Enabling RSTP-

PV disables other spanning tree modes on the switch. The switch cannot 

operate with some ports configured to operate in standard spanning tree 

mode and others to operate in RSTP-PV mode. However, RSTP-PV has 

fallback modes for compatibility with standards-based versions of spanning 

tree.
Access Ports—For an access port, normal IEEE BPDUs will be received and 

sent, though STP-PV or RSTP-PV is enabled on the switch. BPDUs received 

on the access port will be associated with the CST instance.
Trunk Ports—If the native VLAN on an IEEE 802.1Q trunk is VLAN 1:

• VLAN 1 STP BPDUs are sent to the IEEE STP MAC address 

(0180.c200.0000), untagged.

• VLAN 1 STP BPDUs are also sent to the SSTP MAC address, untagged.
• Non-VLAN 1 STP BPDUs are sent to the SSTP MAC address (also called 

the Shared Spanning Tree Protocol [SSTP] MAC address, 0100.0ccc.cccd), 

tagged with a corresponding IEEE 802.1Q VLAN tag.

If the native VLAN on an IEEE 802.1Q trunk is not VLAN 1:

• VLAN 1 STP BPDUs are sent to the SSTP MAC address, tagged with a 

corresponding IEEE 802.1Q VLAN tag.

• VLAN 1 STP BPDUs are also sent to the IEEE STP MAC address on the 

Native VLAN of the IEEE 802.1Q trunk, untagged.

• Non-VLAN 1 STP BPDUs are sent to the SSTP MAC address, tagged with 

a corresponding IEEE 802.1Q VLAN tag.

The DirectLink Rapid Convergence (DRC) feature is designed for an access-

layer switch that has redundant blocked uplinks. It operates on ports blocked 

by spanning tree. DRC can be configured for the entire switch; it cannot be 

enabled for individual VLANs.
The DRC feature is based on the concept of an uplink group. An uplink group 

consists of all the ports that provide a path to the root bridge (the root port 

and any blocked ports). If the root port fails, the blocked port with next 

lowest cost from the uplink group is selected and immediately put in the 

forwarding state without going through the standard spanning tree listening 

and learning states.