Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.14.1.0 - Page 589

Port path cost 20000, Port priority 128, Port Identifier 128.384 Designated root has priority 32768, address 0001.e806.953e Designated bridge has priority 32768, address 0001.e809.c24a Designated port id is 128.384, designated path cost 20000 Number of transitions to forwarding state 1 BPDU (MRecords): sent 39291, received 7547 The port is not in the Edge port mode Influencing MSTP Root Selection MSTP determines the root bridge, but you can assign one bridge a lower priority to increase the probability that it becomes the root bridge. To change the bridge priority, use the following command. • Assign a number as the bridge priority. PROTOCOL MSTP mode msti instance bridge-priority priority A lower number increases the probability that the bridge becomes the root bridge. The range is from 0 to 61440, in increments of 4096. The default is 32768. Example of Assigning and Verifying the Root Bridge Priority By default, the simple configuration shown previously yields the same forwarding path for both MSTIs. The following example shows how R3 is assigned bridge priority 0 for MSTI 2, which elects a different root bridge than MSTI 2. To view the bridge priority, use the show config command from PROTOCOL MSTP mode. R3(conf-mstp)#msti 2 bridge-priority 0 1d2h51m: %RPM0-P:RP2 %SPANMGR-5-STP_ROOT_CHANGE: MSTP root changed for instance 2. My Bridge ID: 0:0001.e809.c24a Old Root: 32768:0001.e806.953e New Root: 0:0001.e809.c24a R3(conf-mstp)#show config ! protocol spanning-tree mstp no disable MSTI 1 VLAN 100 MSTI 2 VLAN 200,300 MSTI 2 bridge-priority 0 Interoperate with Non-Dell Bridges Dell EMC Networking OS supports only one MSTP region. A region is a combination of three unique qualities: • Name is a mnemonic string you assign to the region. The default region name is null. • Revision is a 2-byte number. The default revision number OS is 0. • VLAN-to-instance mapping is the placement of a VLAN in an MSTI. For a bridge to be in the same MSTP region as another, all three of these qualities must match exactly. The default values for the name and revision number must match on all Dell EMC Networking OS devices. If there are non-Dell devices that participate in MSTP, ensure these values match on all devices. NOTE: Some non-Dell devices may implement a non-null default region name. SFTOS, for example, uses the Bridge ID, while others may use a MAC address. Multiple Spanning Tree Protocol (MSTP) 589