Dell Configuration Guide for the S4048–ON System 9.14.2.6

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Modifying Global Parameters

You can modify RSTP parameters.

The root bridge sets the values for forward-delay, hello-time, and max-age and overwrites the values set on other bridges participating in the Rapid Spanning Tree group.

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 RSTP BPDUs.
Max-age — the length of time the bridge maintains configuration information before it refreshes that information by recomputing the RST topology.

NOTE Dell EMC Networking recommends that only experienced network administrators change the Rapid Spanning Tree group parameters. Poorly planned modification of the RSTP parameters can negatively affect network performance.

The following table displays the default values for RSTP.

Table 1. RSTP Default ValuesRSTP Default Values
RSTP Parameter	Default Value
Forward Delay	15 seconds
Hello Time	2 seconds
Max Age	20 seconds
Port Cost: 100-Mb/s Ethernet interfaces 1-Gigabit Ethernet interfaces 10-Gigabit Ethernet interfaces 40-Gigabit Ethernet interfaces Port Channel with 100 Mb/s Ethernet interfaces Port Channel with 1-Gigabit Ethernet interfaces Port Channel with 10-Gigabit Ethernet interfaces Port Channel with 40-Gigabit Ethernet interfaces	Port Cost: 200000 20000 2000 1400 180000 18000 1800 600
Port Priority	128

To change these parameters, use the following commands.

Change the forward-delay parameter.
PROTOCOL SPANNING TREE RSTP mode

forward-delay seconds

The range is from 4 to 30.

The default is 15 seconds.
Change the hello-time parameter.
PROTOCOL SPANNING TREE RSTP 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.
Change the max-age parameter.
PROTOCOL SPANNING TREE RSTP mode

max-age seconds

The range is from 6 to 40.

The default is 20 seconds.

To view the current values for global parameters, use the show spanning-tree rstp command from EXEC privilege mode.