White Papers

Influencing RSTP Root Selection
RSTP determines the root bridge, but you can assign one bridge a lower priority to increase the likelihood that it is selected as
the root bridge.
To change the bridge priority, use the following command.
● Assign a number as the bridge priority or designate it as the primary or secondary root.
PROTOCOL SPANNING TREE RSTP mode
bridge-priority priority-value
○ priority-value The range is from 0 to 65535. The lower the number assigned, the more likely this bridge becomes
the root bridge.
The default is 32768. Entries must be multiples of 4096.
A console message appears when a new root bridge has been assigned. The following example example shows the console
message after the bridge-priority command is used to make R2 the root bridge (shown in bold).
DellEMC(conf-rstp)#bridge-priority 4096
04:27:59: %RPM0-P:RP2 %SPANMGR-5-STP_ROOT_CHANGE: RSTP root changed. My Bridge ID:
4096:0001.e80b.88bd Old Root: 32768:0001.e801.cbb4 New Root: 4096:0001.e80b.88bd
Configuring an EdgePort
The EdgePort feature enables interfaces to begin forwarding traffic approximately 30 seconds sooner.
In this mode an interface forwards frames by default until it receives a BPDU that indicates that it should behave otherwise;
it does not go through the Learning and Listening states. The bpduguard shutdown-on-violation option causes the
interface hardware to be shut down when it receives a BPDU. When only bpduguard is implemented, although the interface is
placed in an Error Disabled state when receiving the BPDU, the physical interface remains up and spanning-tree drops packets
in the hardware after a BPDU violation. BPDUs are dropped in the software after receiving the BPDU violation. This feature is
the same as PortFast mode in Spanning Tree.
CAUTION:
Configure EdgePort only on links connecting to an end station. If you enable EdgePort on an interface
connected to a network, it can cause loops.
Dell EMC Networking OS Behavior: Regarding bpduguard shutdown-on-violation behavior:
● If the interface to be shut down is a port channel, all the member ports are disabled in the hardware.
● When you add a physical port to a port channel already in the Error Disable state, the new member port is also disabled in the
hardware.
● When you remove a physical port from a port channel in the Error Disable state, the error disabled state is cleared on this
physical port (the physical port is enabled in the hardware).
● You can clear the Error Disabled state with any of the following methods:
○ Perform an shutdown command on the interface.
○ Disable the shutdown-on-violation command on the interface (the no spanning-tree stp-id portfast
[bpduguard | [shutdown-on-violation]] command).
○ Disable spanning tree on the interface (the no spanning-tree command in INTERFACE mode).
○ Disable global spanning tree (the no spanning-tree command in CONFIGURATION mode).
To enable EdgePort on an interface, use the following command.
● Enable EdgePort on an interface.
INTERFACE mode
spanning-tree rstp edge-port [bpduguard | shutdown-on-violation]
To verify that EdgePort is enabled on a port, use the show spanning-tree rstp command from EXEC privilege mode or
the show config command from INTERFACE mode.
NOTE: Dell EMC Networking recommends using the show config command from INTERFACE mode.
In the following example, the bold line indicates that the interface is in EdgePort mode.
DellEMC(conf-if-te-2/1)#show config
!
Rapid Spanning Tree Protocol (RSTP)
733