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Dell EMC Configuration Guide for the S4048T–ON System 9.14.2.4

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Modifying Global Parameters

The root bridge sets the values for forward-delay, hello-time, max-age, and max-hops and overwrites the values set on other MSTP bridges.

  • Forward-delay — the amount of time an interface waits in the Listening state and the Learning state before it transitions to the Forwarding state.
  • 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.

Example of the forward-delay Parameter

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)#

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