Glossary

● Hello-time — the time interval in which the bridge sends MSTP bridge protocol data units (BPDUs).
● Max-age — the length of time the bridge maintains configuration information before it refreshes that information by
recomputing the MST topology.
● Max-hops — the maximum number of hops a BPDU can travel before a receiving switch discards it.
NOTE: Dell EMC Networking recommends that only experienced network administrators change MSTP parameters. Poorly
planned modification of MSTP parameters can negatively affect network performance.
To change the MSTP parameters, use the following commands on the root bridge.
1. Change the forward-delay parameter.
PROTOCOL MSTP mode
forward-delay seconds
The range is from 4 to 30.
The default is 15 seconds.
2. Change the hello-time parameter.
PROTOCOL MSTP mode
hello-time seconds
NOTE: With large configurations (especially those configurations with more ports) Dell EMC Networking recommends
increasing the hello-time.
The range is from 1 to 10.
The default is 2 seconds.
3. Change the max-age parameter.
PROTOCOL MSTP mode
max-age seconds
The range is from 6 to 40.
The default is 20 seconds.
4. Change the max-hops parameter.
PROTOCOL MSTP mode
max-hops number
The range is from 1 to 40.
The default is 20.
To view the current values for MSTP parameters, use the show running-config spanning-tree mstp command from
EXEC privilege mode.
DellEMC(conf-mstp)#forward-delay 16
DellEMC(conf-mstp)#exit
DellEMC(conf)#do show running-config spanning-tree mstp
!
protocol spanning-tree mstp
no disable
name my-mstp-region
MSTI 1 VLAN 100
MSTI 2 VLAN 200-300
forward-delay 16
MSTI 2 bridge-priority 4096
DellEMC(conf)#
Modifying the Interface Parameters
You can adjust two interface parameters to increase or decrease the probability that a port becomes a forwarding port.
● Port cost is a value that is based on the interface type. The greater the port cost, the less likely the port is selected to be a
forwarding port.
● Port priority influences the likelihood that a port is selected to be a forwarding port in case that several ports have the
same port cost.
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Multiple Spanning Tree Protocol (MSTP)