Selecting Stp Root; Stp Root Guard - Dell S6100 Configuration Manual

Configured hello time 2, max age 20, forward delay 15
Interface
Name PortID Prio Cost
------------ -------- ---- ------- --- ------- --------------------
Te 1/1/6/1 128.263 128
Te 1/1/7/1 128.264 128
Interface
Name Role PortID
------------ ------ -------- ---- ------- --- ----------------
Te 1/1/6/1 Root 128.263 128
Te 1/1/7/1 ErrDis 128.264 128
Dell(conf-if-te-1/1/7/1)#do show ip interface brief tengigabitEthernet 1/1/7/1
Interface
TenGigabitEthernet 1/1/7/1 unassigned YES Manual up

Selecting STP Root

The STP determines the root bridge, but you can assign one bridge a lower priority to increase the likelihood that it becomes the root
bridge. You can also specify that a bridge is the root or the secondary root.
To change the bridge priority or specify that a bridge is the root or secondary root, use the following command.
• Assign a number as the bridge priority or designate it as the root or secondary root.
PROTOCOL SPANNING TREE mode
bridge-priority {priority-value | primary | secondary}
• priority-value: the range is from 0 to 65535. The lower the number assigned, the more likely this bridge becomes the root
bridge.
The primary option specifies a bridge priority of 8192.
The secondary option specifies a bridge priority of 16384.
The default is 32768.
Example of Viewing STP Root Information
To view only the root information, use the show spanning-tree root command from EXEC privilege mode.
Dell#show spanning-tree 0 root
Root ID Priority 32768, Address 0001.e80d.2462
We are the root of the spanning tree
Root Bridge hello time 2, max age 20, forward delay 15
Dell#

STP Root Guard

Use the STP root guard feature in a Layer 2 network to avoid bridging loops. In STP, the switch in the network with the lowest priority (as
determined by STP or set with the bridge-priority command) is selected as the root bridge. If two switches have the same priority,
the switch with the lower MAC address is selected as the root. All other switches in the network use the root bridge as the reference used
to calculate the shortest forwarding path.
Because any switch in an STP network with a lower priority can become the root bridge, the forwarding topology may not be stable. The
location of the root bridge can change, resulting in unpredictable network behavior. The STP root guard feature ensures that the position of
the root bridge does not change.
Designated
Sts Cost Bridge ID
20000 FWD 20000 32768 0001.e805.fb07 128.653
20000 EDS 20000 32768 0001.e85d.0e90 128.264
Prio Cost Sts Cost
20000 FWD 20000 P2P
20000 EDS 20000 P2P
IP-Address OK Method
PortID
Link-type Edge
No
No
Status Protocol
up
Spanning Tree Protocol (STP) 873