Influencing Mstp Root Selection; Interoperate With Non-Dell Bridges - Dell S4048–ON Configuration Manual

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 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 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.
582 Multiple Spanning Tree Protocol (MSTP)