Switch 7700 Configuration Guide

Implementing STP on the Switch 7700 167
is enabled, an assignment of a priority to the bridge will lead to recalculation of
the spanning tree.
By default, the priority of the bridge is 32768.
Specifying the Switch as a Primary or Secondary Root Switch
RSTP can determine the spanning tree root through calculation. You can also
specify the current switch as the root using this command.
Perform the following configuration in system view.
After a switch is configured as primary root switch or secondary root switch, you
can’t modify the bridge priority of the switch.
A switch can either be a primary or secondary root bridge, but not both.
If the primary root of a spanning tree instance is down or powered off, the
secondary root takes its place, unless you configure a new primary root. Of two or
more configured secondary root switches, RSTP selects the one with the smallest
MAC address to take the place of the failed, primary root.
Note:
■ 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.
■ 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 should designate one primary root and more than one
secondary root bridges per spanning tree domain.
By default, a switch is neither the primary root nor the secondary root of the
spanning tree.
Setting the Forward Delay of a Specified Bridge
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 frame right away, an occasional loop can
occur. Therefore, the root port and the designated port must undergo a transition
state for a period of the forward delay before they transition to the forwarding
Tabl e 6 Specify the Switch as Primary or Secondary Root Switch
Operation Command
Configure the switch as the
primary root switch of the
spanning tree.
stp root primary
Configure the switch as the
secondary root switch of the
spanning tree.
stp root secondary
Disqualify the current switch
as the primary or secondary
root.
undo stp root