3Com SuperStack 4 Configuration Manual page 237

Set Forward Delay of a
Specified Bridge
Set Hello Time of the
Specified Bridge
To configure a Switch as the root of the spanning tree instance, you can specify its
priority as 0 or simply set it as the root, using the command.
It is not necessary to specify two or more roots for an STI — do not specify the
root for an STI on two or more Switches.
You can configure more than one secondary root for a spanning tree through
specifying the secondary STI root on two or more Switches.
Generally, you are recommended to designate one primary root and more than
one secondary roots for a spanning tree.
By default, a Switch is neither the primary root nor the secondary root of the
spanning tree.
Link failure will cause recalculation of the spanning tree and change its structure.
However, the newly calculated configuration BPDU cannot be propagated
throughout the network immediately. If the newly selected root port and
designated port begin to forward data frames right away, this can cause an
occasional loop. Accordingly, the protocol adopts a state transition mechanism,
that is, the root port and the designated port must undergo a transition state for a
period of Forward Delay before they transition to the forwarding state and resume
data frame forwarding. This delay ensures that the new configuration BPDU has
been propagated throughout the network before the data frame forwarding is
resumed.
You can use the following command to set the Forward Delay for a specified
bridge.
Perform the following configurations in System View.
Table 271 Set Forward Delay of a Specified Bridge
Operation
Set Forward Delay of a specified bridge
Restore the default Forward Delay of
specified bridge
Forward Delay of the bridge is related to the diameter of the Switching network.
As a rule, the larger the network diameter, the longer the Forward Delay. Note
that if the Forward Delay is configured too short, occasional path redundancy may
occur. If the Forward Delay is configured too long, restoring the network
connection may take a long time. It is recommended to use the default setting.
By default, the bridge Forward Delay is 15 seconds.
A bridge transmits hello packet regularly to the adjacent bridges to check if there
is link failure.
You can use the following command to set the Hello Time of a specified bridge.
Perform the following configurations in System View.
RSTP Configuration
Command
stp timer forward-delay
centiseconds
undo stp timer forward-delay
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