Advanced Traffic Management Guide K/KA/KB.15.15

When configuring or reconfiguring MSTP, the switch recalculates the corresponding network paths.
This can have a ripple effect throughout your network as adjacent MSTP switches recalculate
network paths to support the configuration changes invoked in a single switch. Although MSTP
employs rapid spanning tree operation, the convergence time for implementing MSTP changes
can be disruptive to your network. However, by using the spanning-tree pending feature,
you can set up an MSTP on the switch and then invoke all instances of the new configuration at
the same time, instead of one at a time.
Syntax:
[no] spanning-tree pending [ apply | config-name | config-revision |
instance | reset ]
Exchanges the currently active MSTP configuration with the current pending MSTP
configuration. Options are as follows:
apply Exchanges the currently active MSTP
configuration with the pending MSTP
configuration.
config-name Specifies the pending MST region name.
Must be the same for all MSTP switches in
the region. (Default: The switch's MAC
address.)
config-revision Specifies the pending MST region
configuration revision number. Must be the
same for all MSTP switches in the region.
(Default: 0).
instance 1..16 vlan [ vid |
vid-range ]
Creates the pending instance and assigns
one or more VLANs to the instance.
reset Copies the switch's currently active MSTP
configuration to the pending configuration.
This is useful when you want to experiment
with the current MSTP configuration while
maintaining an unchanged version.
Creating a pending MSTP configuration
To create a pending MSTP configuration and exchange it with the active MSTP configuration:
1. Configure the VLANs to include in any instances in the new region. When you execute the
pending command, all VLANs configured on the switch will be assigned to a single pending
IST instance unless assigned to other, pending MST instances. The pending command creates
the region's IST instance automatically.
2. Configure MSTP as the spanning tree protocol, then execute write mem and reboot. The
pending option is available only with MSTP enabled.
3. Configure the pending region config-name to assign to the switch.
4. Configure the pending config-revision number for the region name.
5. If you want an MST instance other than the IST instance, configure the instance number and
assign the appropriate VLANs (VIDs) using the
pending instance 1..16 vlan [ vid | vid-range ]
command.
6. Repeat step 5 for each additional MST instance necessary.
7. To review your pending configuration, use the show spanning-tree pending command.
8. To exchange the currently active MSTP configuration with the pending MSTP configuration,
use the spanning-tree pending apply command.
94 Multiple instance spanning tree operation