This document describes the procedure to collapse multiple Spanning
Tree Protocol (STP) instances into a single STP instance in order to overcome
the limitation of eight STP instances for every 15454 node.
Cisco recommends that you have knowledge of these topics:
Cisco ONS 15454
Spanning Tree Protocol
The information in this document is based on these software and
The information in this document was created from the devices in a
specific lab environment. All of the devices used in this document started with
a cleared (default) configuration. If your network is live, make sure that you
understand the potential impact of any command.
Technical Tips Conventions for more information on document
This document uses a lab setup with four ONS 15454 nodes, namely
15454a-105, 15454b-108, 15454c-107 and 15454d-104 (see Figure 1). These four nodes form a star network, where
15454a-105 serves as the common point.
Figure 1 – Topology
Each node has one E100T-12 card.
The spanning tree software on the ONS 15454 runs on the Timing,
Communications and Control (TCC) card, which is a shared resource.
Note: This document uses 'TCC' to generically refer to all variations of
This document addresses the limitation of a maximum of eight STP
instances for a node.
Complete these steps in order to understand the
Log into the Cisco Transport Controller (CTC) for
Figure 2 – Expanded STP Instances
Click the Maintenance tab (see arrow A in
Click the Ether Bridge tab (see arrow B in
Click the Circuits tab (see arrow C in
The STP ID column displays eight different instances of STP. An
attempt to create a circuit with a ninth STP instance fails with an error
message (see Figure 3).
Figure 3 – VLAN/Spanning Tree Violation Error
One way to avoid the error is to assign phantom VLANs that do not carry
traffic. A phantom VLAN forces the spanning tree to collapse into the same
instance. The solution is to collapse Circuit 1, Circuit 2, Circuit 3 and
Circuit 4 into one STP instance.
Complete these steps:
Create a phantom VLAN. Complete these steps:
Log into CTC for 15454a-105.
Click the Circuits tab (see Arrow A in
Select Circuit 1 (see arrow B in
Figure 4 – Edit the Circuit
Click Edit (see arrow C in Figure 4). The Edit Circuit window appears (see
Observe the circuit map (see arrow A in Figure 5).
Note: In order to view the circuit map, you must check the
Show Detailed Map check box (see arrow D in
Figure 5 – Edit Circuit: Circuit 1
Click the VLANs tab (see arrow B in
Click New VLAN (see arrow C in ). The Define New VLAN dialog box appears.
Figure 6 – Define New VLAN
Enter the VLAN Name and VLAN Id in the appropriate fields. In
this case, the VLAN Name is VLAN99 and VLAN Id is 99.
Add VLAN99 to Circuit 1. Complete these steps:
Select VLAN99 from the Available VLANs (see arrow A in
Figure 7 – Add a VLAN to a Circuit
Click the >> button (see arrow B in
Click Apply (see arrow C in Figure 7).
Add VLAN99 to Circuit 2.
Add VLAN99 to Circuit 3.
Add VLAN99 to Circuit 4.
Complete these steps in order to verify the result:
Click Maintenance > Ether Bridge >
Compare arrow D in Figure 2 and arrow A
in Figure 8. Observe that circuits 2, 3 and 4
collapse into STP ID 1 from STP ID 2, 3 and 4.
Figure 8 – Collapsed STP Instance
After the merge, the number of STP instances successfully reduces from
8 to 5. Now you can add another STP instance.