Chapter 11 Managing Network Spanning Trees
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Table Of Contents
Managing Network Spanning Trees
Understanding Spanning Tree Protocol
Per VLAN Spanning Tree Protocol
Multiple Spanning Tree Protocol
Multiple Instance Spanning Tree Protocol
Spanning Tree Recommendation Reports
Spanning Tree Reports: Optimal Root Recommendation Report
Interpreting Optimal Root Recommendation
Spanning Tree Reports: Number of Instances Recommendation Report
Interpreting Number of Instances Recommendation
Spanning Tree Reports: Instance Reduction Recommendation Report
Interpreting Instance Reduction Recommendation
Spanning Tree Reports: VLAN to Instance Mapping Recommendation Report
Interpreting VLAN to Instance Mapping Recommendation
Spanning Tree Reports: STP Visualizer
Generating Reports and Configuring STP on the Network
Reporting and Configuring PVST Port
Reporting and Configuring MST Port
Reporting and Configuring MISTP Port
Reporting and Configuring PVST Device
Reporting and Configuring MST Device
Reporting and Configuring MISTP Device
Reporting and Configuring MST Instance
Reporting and Configuring MISTP Instance
Reporting and Configuring PVST Trunk
Reporting and Configuring MST Trunk
Reporting and Configuring MISTP Trunk
Viewing STP Loop Inconsistency
Viewing STP PVID Inconsistency
Viewing STP Root Inconsistency
Viewing STP Type Inconsistency
STP Filters in Switch Cloud View
Viewing Spanning Tree per IEEE 802.1s Instance
Viewing Spanning Tree per Cisco MISTP Instances
Viewing VLANs in Switch Clouds
Managing Network Spanning Trees
This chapter describes, the IEEE 802.1d Spanning Tree Protocol (STP), and how to use and configure Cisco's proprietary spanning-tree protocols, Per VLAN Spanning Tree (PVST), Multiple Spanning Tree (MSTP), and Multi-Instance Spanning Tree Protocol (MISTP) in a Campus network. It contains the following sections:
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Understanding Spanning Tree Protocol
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Understanding Spanning Tree Protocol
Spanning Tree Protocol (STP) is a link management protocol that provides path redundancy while preventing undesirable loops in the network. Hence, STP is a loop-prevention protocol.
It is a technology that allows Bridges to communicate with each other to discover physical loops in the network. The protocol then specifies an algorithm that Bridges can use to create a loop-free logical topology.
In other words, STP creates a tree structure of loop-free leaves and branches that spans the entire Layer 2 network.
To provide path redundancy STP spans all switches in an extended network. STP forces certain redundant data paths into a standby (blocked) state.
This section describes the specific functions available to you when you use spanning-tree protocols. STP uses a distributed algorithm that selects one Bridge of a redundantly connected network as the root of a Spanning Tree-connected active topology.
STP assigns roles to each port depending on what the port's function is in the active topology. Port roles are:
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Designated, Alternate, and Backup states are specific to MST.
The switches that have ports with these assigned roles are called the root or designated switches.
In Ethernet networks, only one active path may exist between any two stations. Multiple active paths between stations can cause loops in the network.
When loops occur, some switches recognize the same stations on more than one side of the switch. This situation causes the forwarding algorithm to malfunction allowing the duplicate frames to be forwarded.
The Spanning Tree algorithms provide path redundancy by defining a tree that spans all of the switches in an extended network and then forces certain redundant data paths into a standby (blocked) state.
At regular intervals, the switches in the network send and receive Spanning Tree BPDUs that they use to identify the path.
If one network segment becomes unreachable, or if the Spanning Tree costs change, the Spanning Tree algorithm reconfigures the Spanning Tree topology and reestablishes the link by activating the standby path.
The Spanning Tree operation is transparent to end stations, which do not detect whether they are connected to a single LAN segment or a switched LAN of multiple segments.
STP provides these advantages:
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These sections describe the following Spanning Tree Protocols in brief:
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Per VLAN Spanning Tree Protocol
Per VLAN Spanning Tree Protocol maintains a separate instance of STP for each individual VLAN configured in the network.
It allows a VLAN trunk to be forwarding for some VLANs while blocking for other VLANs. Since PVST treats each VLAN as a separate network, it has the ability to load balance traffic (at layer 2). It does this by forwarding some VLANs on one trunk and other VLANs on another trunk without causing a Spanning Tree loop.
Multiple Spanning Tree Protocol
Multiple Spanning Tree uses IEEE's RSTP as base Spanning Tree Protocol. MST uses only one BPDU for all instances.
A disadvantage of PVST is that it adds a lot of overhead to your switching equipment. If a switch is configured to use MST, it must ascertain which of its neighbors are using which type of STP.
It does this by configuring switches into common MST regions, where every switch in a region runs MST with compatible parameters. You can map a group of VLANs to instance.
In most networks, a single MST region is sufficient, although you can configure more than one region. Within the region, all switches must run the instance of MST that is defined by the following attributes:
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Multiple Instance Spanning Tree Protocol
Multiple Instance Spanning Tree Protocol (MISTP) allows you to group multiple VLANs under a single instance of Spanning Tree (an MISTP instance).
An MISTP instance is a virtual logical topology that is defined by a set of bridge and port parameters. When you map VLANs to an MISTP instance, this virtual logical topology becomes a physical topology.
Each MISTP instance has its own root switch and a different set of forwarding links, that is, different bridge and port parameters.
Each MISTP instance root switch propagates the information that is associated with it to all other switches in the network. This process maintains the network topology. This is because it ensures that each switch has the same information about the network.
MISTP builds MISTP instances by exchanging MISTP BPDUs with peer entities in the network. MISTP uses one BPDU for each MISTP instance
An MISTP instance can have any number of VLANs that are mapped to it, but a VLAN can be mapped only to a single MISTP instance.
You can move a VLAN (or VLANs) in an MISTP instance to another MISTP instance if it has converged.
Spanning Tree Recommendation Reports
Campus Manager Recommendation Reports aid deployment of Spanning Trees in the network. The following reports are available:
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Spanning Tree Reports: Optimal Root Recommendation Report
The Optimal Root Recommendation Report allows you to compute the optimal root in a switch cloud running Per VLAN STP, Cisco MISTP, or IEEE 802.1s.
Step 1
Step 2
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The Optimal Root Recommendation window appears.
Step 3
Table 11-1 lists three computation types and their description.
If you select Traffic Data, go to Step 4, else go to Step 5.
Step 4
Step 5
The Recommended Roots table lists the optimal root devices.
Step 6
Step 7
Interpreting Optimal Root Recommendation
The optimal root recommendation report helps you to select the best root for your network using any of the three methods:
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Use this method to compute better overall convergence. Convergence time is based on the distance to the boundary nodes. The node with the least path cost to boundary nodes is recommended as optimal root.
A device farther from the boundary nodes takes longer to propagate the topology change that has occurred than another node that is near the boundary nodes in the same switched environment.
This directly affects the convergence time of the switched or bridged network. After this root is selected, you can make suitable adjustments to forward the delay timer of Spanning Tree protocol to take advantage of faster convergence.
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The node with the least cumulative cost to all other nodes is recommended as root according to this method. When Spanning Tree root is computed based on this method it provides a better path between nodes in the switched environment assuming equal traffic distributions.
In case of unbalanced switched environment where core switch A is connected to 10 other distribution switches and another core switch B is connected to only 5 of the distribution switches, this algorithm will suggest A as root as compared to B.
Five switches that are not directly connected to B should take a longer path to other nodes if B is selected as root. If A is selected as root this problem could be avoided.
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In a switched or bridged network environment, when Spanning Tree is computed the primary aim is to eliminate loops and it may not provide shortest possible path between every node to every other node.
Based on the traffic pattern a particular device may provide optimal path for a greater percentage of traffic than another.
For example, a switched network containing nodes—A, B, C, D, and E. Overall traffic is 95% localized between a set of nodes {A, B, and C}. A node which when selected as root, provides the shortest path between A, B, and C would be the ideal choice. This is regardless of whether it provides shortest path from D or E to any other nodes.
In some cases you may not be able to get the shortest path between A, B, and C when trying to find the optimal root. In such cases, a root that provides most optimal path between A, B, and C is chosen.
Spanning Tree Reports: Number of Instances Recommendation Report
The Number of Instances Recommendation Report allows you to compute the number of instances in a switch cloud running Cisco MISTP or IEEE 802.1s.
Step 1
Step 2
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The Number of Instance Recommendation window appears.
Step 3
Table 11-3 lists two computation techniques and their description.
Step 4
The Recommended Number of Instances appears in the Results area.
Step 5
Step 6
Step 7
Interpreting Number of Instances Recommendation
The number of instance recommendation is made based on two methods:
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Use this method to compute better balanced link utilization.
We recommend that you use the number of instances that is the least common multiplier of all the independent redundant paths, as the maximum number of instances.
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Use this method to compute a minimum number of instances so that CPU utilization is minimum.
We recommend that the number of instances, which results in the maximum number of independent redundant paths is recommended.
Spanning Tree Reports: Instance Reduction Recommendation Report
The Instances Reduction Recommendation Report allows you to compute the number of instances in a switch cloud running Cisco MISTP or IEEE 802.1s.
Step 1
Step 2
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The Instance Reduction Recommendation window appears.
Step 3
Table 11-4 lists two computation techniques and their description.
Step 4
The Recommended Number of Instances in displayed in the table.
Table 11-5 Instance Reduction Results
Instance
Instance ID.
Mergeable Instances
Comma separated list of instance IDs which can be merged.
Step 5
Step 6
Interpreting Instance Reduction Recommendation
You can use the Instance Reduction Recommendations if your network contains multiple Spanning Tree instances that share the same forwarding topology.
The Recommendation report allows you to determine Spanning Tree instances. These instances can be merged into a shared instance without any impact on convergence or operation.
Fewer instances help you to optimize the utilization of memory and CPU resources of the switches. Instance reduction recommendation is made based on two methods:
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Use this method to determine Spanning Tree instances, which can be merged when the switched network has an instance that spans across different sets of switches as compared to another instance.
For example, instance A is considered a sub-tree of instance B if all the forwarding and blocking paths of instance A are in the same state in instance B. Instance A is a sub-tree of instance B if the forwarding and blocking paths of instance A exactly matches that of instance B.
If the above case is satisfied, the report recommends merging of the two STP instances.
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Use this method to determine the Spanning Tree instances, which can be merged when the switched network has instances that share forwarding paths and root.
Spanning Tree Reports: VLAN to Instance Mapping Recommendation Report
The Number of Instances Recommendation Report allows you to compute the optimum number of VLANs to instances in a switch cloud running Cisco MISTP or IEEE 802.1s.
Step 1
Step 2
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The VLAN to Instance Mapping Recommendation window appears.
Step 3
If you select Least instance load or Least instance load for selected devices, go to Step 4, else go to Step 5.
Step 4
Step 5
The Recommended Instance ID is displayed in the VLAN Instance Recommendation area.
Step 6
Step 7
Interpreting VLAN to Instance Mapping Recommendation
The number of instance recommendation is made based on four methods:
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Use this method when the traffic or load on each of the VLANs is almost the same. This method assumes that an instance with least number of VLANs is optimal for mapping to a new VLAN. Hence, the Spanning Tree instances with the least number of VLANs mapped to it will be recommended.
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You can provide the information on devices, which will be part of the new VLAN to be created. This method determines the optimal path for various available instances for the selected devices.
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The projected traffic of the new VLAN you selected is used, and the instance which has least overall traffic is recommended.
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This method assumes that the devices you selected will be part of the new VLAN. Based on this information, the instance with the least load that is spread across the devices you selected is recommended.
Spanning Tree Reports: STP Visualizer
The STP Visualizer allows you to test changes to STP settings before you enforce them on a network.
To view the STP Visualizer:
Step 1
Step 2
The Spanning Tree Visualizer window appears.
Step 3
Depending on the Spanning Tree Protocol the device is running, one of the following appears:
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Step 4
To view the devices in the VLAN Region, click Select. The ID of the selected Spanning Tree instance is displayed in the Selected Instance ID field.
Step 5
To view the Spanning Tree details of an MST Instance in the Network Topology View window, click Select. The ID of the selected Spanning Tree instance is displayed in Selected Instance ID field.
Step 6
To view the Spanning Tree details of an MIST Instance in the Network Topology View window, click Select. The ID of the selected Spanning Tree instance is displayed in Selected Instance ID field.
The devices in the VLAN instance appear in a table. Table 11-11 lists the fields in the table, their description, and usage notes for editable fields.
Table 11-11 Port Details
Device Name
Name of the device.
This field is not configurable.
IP Address
Displays the IP address of the device.
This field is not configurable.
Port
Displays the port name.
This field is not configurable.
In case of device priority, this field displays NA.
Type
Displays the Spanning Tree type:
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This field is not configurable.
Existing
Lists the current port priority or cost value.
This field is not configurable.
New*
Lists the new port priority or cost that you have entered.
Enter a new value.
1 Field marked with asterisk is editable.
To edit values of fields marked with an asterisk:
a.
The selected rows are highlighted in the Edit Here section.
b.
The changed values are displayed, highlighted in pink.
c.
Interpreting STP Visualizer
The STP Visualizer allows you to:
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STP Visualizer Notes
STP Visualizer cannot suggest the correct configuration in the following scenarios:
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Generating Reports and Configuring STP on the Network
You can generate reports and configure STP on switch clouds for the following:
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Reporting and Configuring PVST Port
To configure PVST port on a switch cloud:
Step 1
The Spanning Tree Configuration page appears.
Step 2
The Spanning Tree Port Configuration page appears.
Step 3
Step 4
The Select Instance dialog box appears.
Step 5
Step 6
The devices in the VLAN instance appear in a table. Table 11-13 lists the fields in the table, their description, and usage notes for editable fields.
Table 11-13 PVST Port Details
Device Name
Name of the device.
This field is not configurable.
IP Address
IP address of the device.
This field is not configurable.
Port
Port number used for bridge forwarding.
This field is not configurable.
isLink
Displays a check mark if the port is a link port.
This field is not configurable.
State
State of the port. The possible states are:
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This field is not configurable.
Cost*
Port cost value.
The STP port path cost default value is derived from the media speed of a LAN interface.
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You can assign lower cost values to LAN interfaces that you want STP to maintain in a forwarding state.
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The possible cost range is 0 through 65535 (the default is media specific).
STP uses the port cost value when the LAN interface is configured as an access port and uses VLAN port cost values when the LAN interface is configured as a trunk port.
Priority*
Port priority.
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Priority is taken into account after examining cost and sending bridge ID. That is, if the cost and bridge ID is the same, priority is considered.
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Designated Bridge
Bridge ID for the designated bridge.
The Designated Bridge provides the minimum root path cost on a LAN.
Also, it is the only bridge allowed to forward frames to and from the LAN for which it is the designated bridge.
This field is not configurable.
Designated Port
ID of the port that connects a LAN to the designated bridge.
This field is not configurable.
PortFast*
State of the PortFast Interface Configuration feature:
Enable or Disable.
Select a value from the drop-down list.
When enabled, PortFast causes a switch or trunk port interface to enter the Spanning Tree forwarding state immediately, bypassing the listening and learning states.
Loop Guard*
State of the Loop Guard feature:
Enable or Disable.
Select a value from the drop-down list.
When enabled, Loop Guard works on non-designated ports and does not allow the port to become designated via max_age expiry.
BPDU Guard*
State of the BPDU Guard feature:
Enabled, Disabled or Default.
Select a value from the drop-down list.
When enabled, BPDU Guard feature prevents loops by moving a nontrunking port into an errdisable state when a BPDU is received on that port.
When the BPDU guard feature is enabled on the switch, Spanning Tree shuts down PortFast-configured interfaces that receive BPDUs, instead of putting them into the Spanning Tree blocking state.
BPDU Filter*
State of the BPDU filter feature:
Enabled, Disabled or Default.
Select a value from the drop-down list.
When enabled, BPDU filtering allows you to avoid transmitting BPDUs on a port, usually connected to an end system.
When you enable PortFast on the switch, Spanning Tree places ports in the forwarding state immediately, instead of going through the listening, learning, and forwarding states.
Root Guard*
State of the Root Guard feature:
Enable or Disable.
Select a value from the drop-down list.
When enabled, Root Guard does not allow the port to become non-designated.
1 Fields marked with asterisk are editable.
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The selected rows are highlighted in the Edit Here section.
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or
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The new values are displayed, highlighted in pink.
Step 7
Or
Click Reset to return to the previous values without making any changes.
Reporting and Configuring MST Port
To configure MST port on a switch cloud:
Step 1
The Spanning Tree Configuration page appears.
Step 2
The Spanning Tree Port Configuration page appears.
Step 3
Step 4
The Select Instance dialog box appears.
Step 5
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The devices running the selected MST instance appear in a table. Table 11-15 lists the fields in the table, their description, and usage notes for editable fields.
Table 11-15 MST Port Details
Device Name
Name of the device
This field is not configurable.
IP Address
IP address of the device
This field is not configurable.
Port
Port number used for bridge forwarding
This field is not configurable.
isLink
Displays a check mark if the port is a link port
This field is not configurable.
LinkType
Link type of the port. The possible link types are:
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By default, the switch derives the link type of a port from the duplex mode.
A full-duplex port is considered as a point-to-point link while a half-duplex configuration is assumed to be on a shared link.
This field is not configurable.
Cost*
Port cost value
The STP port path cost default value is derived from the media speed of a LAN interface.
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You can assign lower cost values to LAN interfaces that you want STP to select first and higher cost values to LAN interfaces that you want STP to select last.
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The possible cost range is 0 through 65535 (the default is media specific).
STP uses the port cost value when the LAN interface is configured as an access port and uses VLAN port cost values when the LAN interface is configured as a trunk port.
Priority*
Port priority
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You can assign higher priority values to LAN ports that you want STP to select first and lower priority values to LAN ports that you want STP to select last.
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State
State of the port. The possible states are:
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This field is not configurable.
Status
Indicates if the port lies in the boundary of an MST region.
If yes, the status is shown as Boundary.
If not, the field is left blank.
In generic terms, a port is at the boundary of a region:
If the designated bridge on its segment is in a different region
Or
If it receives legacy 802.1d BPDUs.
Role
Role of the port. The possible roles are:
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MST assigns port roles as follows:
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This field is not configurable.
Designated Bridge
Bridge ID for the designated bridge.
The Designated Bridge provides the minimum root path cost on a LAN.
Also, it is the only bridge allowed to forward frames to and from the LAN for which it is the designated bridge.
This field is not configurable.
Designated Port
Displays the ID of the port that connects a LAN to the designated bridge
This field is not configurable.
PortFast*
Displays the state of the PortFast Interface Configuration feature:
Enabled or Disabled
Select a value from the drop-down list.
When enabled, PortFast causes a switch or trunk port interface to enter the Spanning Tree forwarding state immediately, bypassing the listening and learning states.
Loop Guard*
Displays the state of the Loop Guard feature:
Enable or Disable.
Select a value from the drop-down list.
When enabled, Loop guard works on non-designated ports and does not allow the port to become designated via max_age expiry.
BPDU Guard*
Displays the state of the BPDU Guard feature:
Enabled, Disabled or Default.
Select a value from the drop-down list.
When enabled, BPDU Guard feature prevents loops by moving a nontrunking port into an enable state when a BPDU is received on that port.
When the BPDU Guard feature is enabled on the switch, Spanning Tree shuts down PortFast-configured interfaces that receive BPDUs, instead of putting them into the Spanning Tree blocking state.
BPDU Filter*
Displays the state of the BPDU filter feature:
Enabled, Disabled or Default.
Select a value from the drop-down list.
When enabled, BPDU filtering allows you to avoid transmitting BPDUs on a port, usually connected to an end system.
When you enable PortFast on the switch, Spanning Tree places ports in the forwarding state immediately, instead of going through the listening, learning, and forwarding states.
Root Guard*
Displays the state of the Root guard feature:
Enabled or Disabled.
Select a value from the drop-down list.
When enabled, Root Guard does not allow the port to become non-designated.
1 Fields marked with asterisk are editable.
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The selected rows are highlighted in the Edit Here section.
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or
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The new values appear, highlighted in pink.
Step 6
Or
Click Reset to return to the previous values without making any changes.
Reporting and Configuring MISTP Port
To configure MISTP port on a switch cloud:
Step 1
The Spanning Tree Configuration page appears.
Step 2
The Spanning Tree Port Configuration page appears.
Step 3
Step 4
The Select Instance dialog box appears.
Step 5
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The devices running the selected MIST instance appear in a table. Table 11-17 lists the fields in the table, their description, and usage notes for editable fields.
Table 11-17 MISTP Port Details
Device Name
Name of the device
This field is not configurable.
IP Address
IP address of the device
This field is not configurable.
Port
Port number used for bridge forwarding
This field is not configurable.
isLink
Displays a check mark if the port is a link port
This field is not configurable.
State
State of the port. The possible states are:
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This field is not configurable.
Cost*
Port cost value
The STP port path cost default value is derived from the media speed of a LAN interface.
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You can assign lower cost values to LAN interfaces that you want STP to select first and higher cost values to LAN interfaces that you want STP to select last.
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The possible cost range is 0 through 65535 (the default is media specific).
STP uses the port cost value when the LAN interface is configured as an access port and uses VLAN port cost values when the LAN interface is configured as a trunk port.
Priority*
Port priority
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You can assign higher priority values to LAN ports that you want STP to select first and lower priority values to LAN ports that you want STP to select last.
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Designated Bridge
Bridge ID for the designated bridge.
The Designated Bridge provides the minimum root path cost on a LAN.
Also, it is the only bridge allowed to forward frames to and from the LAN for which it is the designated bridge.
This field is not configurable.
Designated Port
ID of the port that connects a LAN to the designated bridge.
This field is not configurable.
PortFast*
State of the PortFast Interface Configuration feature:
Enabled or Disabled.
Select a value from the drop-down list.
When enabled, PortFast causes a switch or trunk port interface to enter the Spanning Tree forwarding state immediately, bypassing the listening and learning states.
Loop Guard*
State of the loop guard feature:
Enable or Disable.
Select a value from the drop-down list.
When enabled, Loop Guard works on non-designated ports and does not allow the port to become designated via max_age expiry.
BPDU Guard*
State of the BPDU guard feature:
Enabled, Disabled or Default.
Select a value from the drop-down list.
When enabled, BPDU Guard feature prevents loops by moving a nontrunking port into an errdisable state when a BPDU is received on that port.
When the BPDU Guard feature is enabled on the switch, Spanning Tree shuts down PortFast-configured interfaces that receive BPDUs, instead of putting them into the Spanning Tree blocking state.
BPDU Filter*
State of the BPDU filter feature:
Enabled, Disabled or Default.
Select a value from the drop-down list.
When enabled, BPDU filtering allows you to avoid transmitting BPDUs on a port, usually connected to an end system.
When you enable PortFast on the switch, Spanning Tree places ports in the forwarding state immediately, instead of going through the listening, learning, and forwarding states.
Root Guard*
State of the Root guard feature:
Enabled or Disabled.
Select a value from the drop-down list.
When enabled, Root Guard does not allow the port to become non-designated.
1 Fields marked with asterisk are editable.
•
The selected rows are highlighted in the Edit Here section.
•
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or
–
The new values appear, highlighted in pink.
Step 6
Or
Click Reset to return to the previous values without making any changes.
Reporting and Configuring PVST Device
To configure PVST device on a switch cloud:
Step 1
The Spanning Tree Configuration page appears.
Step 2
The Spanning Tree Device Configuration page appears.
Step 3
PVST details appear in text boxes. Table 11-18 lists the displayed fields and descriptions.
Step 4
The Select Instance dialog box appears.
Step 5
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The devices in the VLAN instance appear in a table. Table 11-20 lists the fields in the table, their description, and usage notes for editable fields.
Table 11-20 PVST Device Details
Device Name
Name of the device.
This field is not configurable.
IP Address
IP address of the device.
This field is not configurable.
Root ID
ID of the bridge assumed to be root. On initialization, each bridge assumes itself as root.
This field is not configurable.
Root Port
ID of the port, which is closest to the root.
This field is not configurable.
Cost Mode
Type of Spanning Tree path cost mode configured on the device.
Applies to all STP instances running on the device.
When you change, the path cost of all ports are reassigned to the default path cost values based on the new Spanning Tree path cost mode and ports' speed. The possible values are:
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This field is not configurable.
Root Cost
Cost of the root.
This field is not configurable.
Extended SysID*
State of the extended system ID feature on the switch:
Enable, Disabled, or Unknown
Select a value from the drop-down list.
STP uses the VLAN ID as the extended system ID. It uses the extended system ID plus a MAC address to make the bridge ID unique for each VLAN. For more details, see Understanding Bridge ID.
Priority*
Bridge priority
The device with the lowest bridge identifier is considered the highest priority bridge and becomes the root bridge. By default, the bridge priority is set to 32768.
Use the bridge priority command to set the priority that the bridge Spanning Tree uses to choose the root bridge in the network.
Bridge priority can range from 0 to 65535. But if you have enabled MAC address reduction, the root bridge priority becomes a multiple of 4096 plus the VLAN ID.
Backbone Fast*
State of the Backbonefast feature:
Enabled or Disabled.
Select a value from the drop-down list.
Uplink Fast*
State of the Uplinkfast feature:
Enabled or Disabled.
Select a value from the drop-down list.
When enabled, UplinkFast feature dramatically decreases the convergence time of the STP in the event of the failure of an uplink on an access switch.
Loop Guard*
State of the Loop Guard feature:
Enable or Disable.
Select a value from the drop-down list.
When enabled, Loop Guard works on non-designated ports and does not allow the port to become designated via max_age expiry.
PortFast Global*
State of the PortFast Global Configuration feature:
Enabled or Disabled.
Select a value from the drop-down list.
When enabled, PortFast causes a switch or trunk port to enter the Spanning Tree forwarding state immediately, bypassing the listening and learning states.
If you configure the default on each port, this setting applies to interfaces.
BPDU Filter*
State of the BPDU Filter feature:
Enabled, Disabled or Default.
Select a value from the drop-down list.
When enabled, BPDU filtering allows you to avoid transmitting BPDUs on a port, usually connected to an end system.
When you enable PortFast on the switch, Spanning Tree places ports in the forwarding state immediately, instead of going through the listening, learning, and forwarding states.
BPDU Guard*
State of the BPDU Guard feature:
Enabled, Disabled or Default.
Select a value from the drop-down list.
When enabled, BPDU Guard feature prevents loops by moving a nontrunking port into an errdisable state when a BPDU is received on that port.
When the BPDU Guard feature is enabled on the switch, Spanning Tree shuts down PortFast-configured interfaces that receive BPDUs, instead of putting them into the Spanning Tree blocking state.
1 Fields marked with asterisk are editable.
•
The selected rows are highlighted in the Edit Here section.
•
–
or
–
The new values are displayed, highlighted in pink.
Step 6
Or
Click Reset to return to the previous values without making any changes.
Reporting and Configuring MST Device
To configure MST port on a switch cloud:
Step 1
The Spanning Tree Configuration page appears.
Step 2
The Spanning Tree Device Configuration page appears.
Step 3
MST details appear in text boxes. Table 11-21 lists the displayed fields and descriptions.
Step 4
The Select Instance dialog box appears.
Step 5
•
The devices in the instance appear in a table. Table 11-23 lists the fields in the table, their description, and usage notes for editable fields.
Table 11-23 MST Device Details
Device Name
Name of the device.
This field is not configurable.
IP Address
IP address of the device.
This field is not configurable.
Root ID
ID of the bridge assumed to be root. Upon initialization, the bridge assumes that it is root.
This field is not configurable.
Root Port
Port ID of the port, which is closest to the root.
This field is not configurable.
Cost Mode
Type of Spanning Tree path cost mode configured on the device.
Applies to all STP instances running on the device.
When you change the value, the path cost of all ports are reassigned to the default path cost values based on the new Spanning Tree path cost mode and ports' speed. The possible values are:
•
•
This field is not configurable.
Root Cost
Cost of the root.
This field is not configurable.
Extended SysID*
State of the extended system ID feature on the switch:
Enable, Disabled, or Unknown
Select a value from the drop-down list.
Priority*
Bridge priority
The device with the lowest bridge identifier is considered the highest priority bridge and becomes the root bridge. By default, the bridge priority is set to 32768.
Use the bridge priority command to set the priority that the bridge Spanning Tree uses to choose the root bridge in the network.
The range for bridge priority is 0 to 65535. The value should be a multiple of 4096.
Region Name*
Alphanumeric configuration name assigned to the MST region that the switch is part of.
Enter a new name in the field to change the region name.
For two or more switches to be in the same MST region, they must have the same VLAN-to-instance map, the same configuration revision number, and the same configuration name.
Region Revision*
MST configuration revision number (0 to 65535).
Enter a new value in the field to change the revision number.
For two or more switches to be in the same MST region, they must have the same VLAN-to-instance map, the same configuration revision number, and the same configuration name.
Max. Hop Count
Number of hops in an MST region after which a BPDU is discarded, and the information held for a port is aged.
(1 to 40; default is 20).
This field is not configurable.
VLANs
List of VLANs that form part of the MST region.
This field is not configurable.
Loop Guard*
State of the Loop Guard feature:
Enable or Disable.
Select a value from the drop-down list.
When enabled, loop guard works on non-designated ports and does not allow the port to become designated via max_age expiry.
PortFast Global*
State of the PortFast Global Configuration feature:
Enabled or Disabled.
Select a value from the drop-down list.
When enabled, PortFast causes a switch or trunk port to enter the Spanning Tree forwarding state immediately, bypassing the listening and learning states.
BPDU Filter*
State of the BPDU filter feature:
Enabled, Disabled or Default.
Select a value from the drop-down list.
When enabled, BPDU filtering allows you to avoid transmitting BPDUs on a port, usually connected to an end system.
When you enable PortFast on the switch, Spanning Tree places ports in the forwarding state immediately, instead of going through the listening, learning, and forwarding states.
BPDU Guard*
State of the BPDU Guard feature:
Enabled, Disabled or Default.
Select a value from the drop-down list.
When enabled, BPDU Guard feature prevents loops by moving a nontrunking port into an errdisable state when a BPDU is received on that port.
When the BPDU Guard feature is enabled on the switch, Spanning Tree shuts down PortFast-configured interfaces that receive BPDUs, instead of putting them into the Spanning Tree blocking state.
1 Fields marked with asterisk are editable.
•
The selected rows are highlighted in the Edit Here section.
•
–
or
–
The new values appear, highlighted in pink.
Step 6
Or
Click Reset to return to the previous values without making any changes.
Reporting and Configuring MISTP Device
To configure MISTP port on a switch cloud:
Step 1
The Spanning Tree Configuration page appears.
Step 2
The Spanning Tree Device Configuration page appears.
Step 3
MISTP details appear in text boxes. Table 11-24 lists the displayed fields and descriptions.
Step 4
The Select Instance dialog box appears.
Step 5
•
The devices in the instance appear in a table. Table 11-26 lists the fields in the table, their description, and usage notes for editable fields.
Table 11-26 MISTP Device Details
Device Name
Name of the device.
This field is not configurable.
IP Address
IP address of the device.
This field is not configurable.
Root ID
ID of the bridge assumed to be root. Upon initialization, the bridge assumes that it is root.
This field is not configurable.
Root Port
Port ID of the port, which is closest to the root.
This field is not configurable.
Cost Mode
Type of Spanning Tree path cost mode configured on the device.
Applies to all STP instances running on the device.
When you change the value, the path cost of all ports will be reassigned to the default path cost values based on the new Spanning Tree path cost mode and ports' speed. The possible values are:
•
•
This field is not configurable.
Root Cost
Cost of the root.
This field is not configurable.
Extended SysID*
State of the extended system ID feature on the switch:
Enable, Disabled, or Unknown
Select a value from the drop-down list.
Priority*
Bridge priority
The device with the lowest bridge identifier is considered the highest priority bridge and becomes the root bridge. By default, the bridge priority is set to 32768.
Use the bridge priority command to set the priority that the bridge Spanning Tree uses to choose the root bridge in the network.
The range for bridge priority is 0 to 65535. The value should be a multiple of 4096.
Backbone Fast*
State of the Backbonefast feature:
Enabled or Disabled.
Select a value from the drop-down list.
Uplink Fast*
State of the Uplinkfast feature:
Enabled or Disabled.
Select a value from the drop-down list.
When enabled, UplinkFast feature dramatically decreases the convergence time of the STP in the event of the failure of an uplink on an access switch.
Loop Guard*
State of the Loop Guard feature:
Enable or Disable.
Select a value from the drop-down list.
When enabled, loop guard works on non-designated ports and does not allow the port to become designated via max_age expiry.
PortFast Global*
State of the PortFast Global Configuration feature:
Enabled or Disabled.
Select a value from the drop-down list.
When enabled, PortFast causes a switch or trunk port to enter the Spanning Tree forwarding state immediately, bypassing the listening and learning states.
BPDU Filter*
State of the BPDU Filter feature:
Enabled, Disabled or Default.
Select a value from the drop-down list.
When enabled, BPDU filtering allows you to avoid transmitting BPDUs on a port, usually connected to an end system.
When you enable PortFast on the switch, Spanning Tree places ports in the forwarding state immediately, instead of going through the listening, learning, and forwarding states.
BPDU Guard*
State of the BPDU Guard feature:
Enabled, Disabled or Default.
Select a value from the drop-down list.
When enabled, BPDU Guard feature prevents loops by moving a nontrunking port into an errdisable state when a BPDU is received on that port.
When the BPDU Guard feature is enabled on the switch, Spanning Tree shuts down PortFast-configured interfaces that receive BPDUs, instead of putting them into the Spanning Tree blocking state.
1 Fields marked with asterisk are editable.
•
The selected rows are highlighted in the Edit Here section.
•
–
or
–
The new values appear, highlighted in pink.
Step 6
Or
Click Reset to return to the previous values without making any changes.
Note
Reporting and Configuring MST Instance
To configure MST instance on a switch cloud:
Step 1
The Spanning Tree Configuration page appears.
Step 2
The Spanning Tree Port Instance Configuration page appears.
Step 3
Step 4
The Select Device dialog box appears.
Step 5
•
The instance and VLAN appear in a table. Table 11-28 lists the fields in the table, their description, and usage notes for editable fields.
Table 11-28 MST Instance Details
Instance
MST instance that the device is part of.
This field is not configurable.
VLANS *
VLANs that are mapped to the instance.
Select a value from the drop-down list.
1 Fields marked with asterisk are editable.
•
The selected rows are highlighted in the Edit Here section.
•
–
Or
–
The new values are displayed, highlighted in pink.
Step 6
Or
Click Reset to return to the previous values without making any changes,.
Reporting and Configuring MISTP Instance
To configure MISTP instance on a switch cloud:
Step 1
The Spanning Tree Configuration page appears.
Step 2
The Spanning Tree Port Instance Configuration page appears.
Step 3
Step 4
The Select Device dialog box appears.
Step 5
Step 6
The instance and VLAN appear in a table. Table 11-30 lists the fields in the table, their description, and usage notes for editable fields.
Table 11-30 MISTP Instance Details
Instance
MISTP instance that the device is part of.
This field is not configurable.
VLANS*
VLANs that the device is part of.
Select a value from the drop-down list.
1 Fields marked with asterisk are editable.
•
The selected rows are highlighted in the Edit Here section.
•
–
or
–
The new values are displayed, highlighted in pink.
Step 7
Or
Click Reset to return to the previous values without making any changes.
Reporting and Configuring PVST Trunk
To configure PVST trunk on a switch cloud:
Step 1
The Spanning Tree Configuration page appears.
Step 2
The Spanning Tree Port Trunk Configuration page appears.
Step 3
Step 4
The Select Device dialog box appears.
Step 5
The instance and VLAN appear in a table. Table 11-32 lists the fields in the table, their description, and usage notes for editable fields.
Table 11-32 PVST Trunk Details
Device Name
Name of the device.
This field is not configurable.
IP Address
IP address of the device.
This field is not configurable.
Port
Trunk port on the device.
This field is not configurable.
isTrunk
Displays a check mark if the port is a trunk port.
This field is not configurable.
Preferred VLANs *
Preferred VLANs the trunk port is configured for.
Preferred VLANs are VLANs you prefer to keep in forwarding mode on a trunk link. You can do this by setting the port instance cost of these VLANs to be lower than the other VLANs.
When port instance cost is lowered these instances are made forwarding on the trunk as against the other.
You can load balance VLAN traffic across multiple trunk links.
For example, if you want to have some VLANs to use only a particular trunk link, then you can lower their STP cost so that they are preferred over that link.
1 Fields marked with asterisk are editable.
•
The selected rows are highlighted in the Edit Here section.
•
•
–
or
–
The new values appear, highlighted in pink.
Step 6
Or
Click Reset to return to the previous values without making any changes.
Note
Reporting and Configuring MST Trunk
To configure MST trunk on a switch cloud:
Step 1
The Spanning Tree Configuration page appears.
Step 2
The Spanning Tree Port Trunk Configuration page appears.
Step 3
Step 4
The Select Device dialog box appears.
Step 5
The instance and VLAN appear in a table. Table 11-34 lists the fields in the table, their description, and usage notes for editable fields.
Table 11-34 MST Trunk Details
Device Name
Name of the device.
This field is not configurable.
IP Address
IP address of the device.
This field is not configurable.
Port
Port number used for bridge forwarding.
This field is not configurable.
isTrunk
Displays a check mark if the port is a trunk port.
This field is not configurable.
Preferred Instance *
Preferred instances the trunk port is configured for.
Preferred VLANs are VLANs you prefer to keep in forwarding mode on a trunk link. You can do this by setting the port instance cost of these VLANs to be lower than the other VLANs.
When port instance cost is lowered, these instances are made forwarding on the trunk as against the other.
You can load balance VLAN traffic across multiple trunk links.
For example, if you want to have some VLANs to use only a particular trunk link, then you can lower their STP cost so that they are preferred over that link.
1 Fields marked with asterisk are editable.
•
The selected rows are highlighted in the Edit Here section.
•
•
–
or
–
The new values appear, highlighted in pink.
Step 6
Or
Click Reset to return to the previous values without making any changes.
Note
Reporting and Configuring MISTP Trunk
To configure MISTP trunk on a switch cloud:
Step 1
The Spanning Tree Configuration page appears.
Step 2
The Spanning Tree Port Trunk Configuration page appears.
Step 3
Step 4
The Select Device dialog box appears.
Step 5
The instance and VLAN appear in a table. Table 11-36 lists the fields in the table, their description, and usage notes for editable fields.
Table 11-36 MST Trunk Details
Device Name
Name of the device.
This field is not configurable.
IP Address
IP address of the device.
This field is not configurable.
Port
Port number used for bridge forwarding.
This field is not configurable.
isTrunk
Displays a check mark if the port is a trunk port.
This field is not configurable.
Preferred Instance *
Preferred instances the trunk port is configured for.
Preferred VLANs are VLANs you prefer to keep in forwarding mode on a trunk link. You can do this by setting the port instance cost of these VLANs to be lower than the other VLANs.
When port instance cost is lowered these instances are made forwarding on the trunk as against the other.
You can load balance VLAN traffic across multiple trunk links.
For example, if you want to have some VLANs to use only a particular trunk link, then you can lower their STP cost so that they are preferred over that link.
1 Fields marked with asterisk are editable.
•
The selected rows are highlighted in the Edit Here section.
•
•
–
or
–
The new values appear, highlighted in pink.
Step 6
Or
Click Reset to return to the previous values without making any changes.
Note
Spanning Tree Filters
Topology Map provides two filters for STP enabled devices or links. These filters are available in the topology maps for Switch Clouds under LAN Edge View.
STP Inconsistency
If your network has incorrect configurations, STP stops functioning and you may lose connectivity. STP Inconsistency detects these incorrect configurations in your network and changes the state to inconsistent for corresponding ports, thus preventing the ports from affecting the network.
When you select the filter, Topology View highlights the link and device associated with that specific STP inconsistency.
STP inconsistencies are computed during each data collection. Devices in the switched clouds are polled when the filter is applied.
Topology Map provides four filters under STP Inconsistency:
•
•
•
•
Spanning Tree
These filters are based on the Spanning Tree details of devices. When you select the filter, topology map lists the Spanning Tree Instances applicable to all the switches in the selected switch cloud. Topology Map provides three filters under Spanning Tree:
•
•
•
Viewing STP Loop Inconsistency
To view STP loop inconsistencies in switch clouds:
Step 1
Step 2
The link and devices with loop inconsistencies appear.
Viewing STP PVID Inconsistency
To view STP PVID inconsistencies in switch clouds:
Step 1
Step 2
The link and devices with PVID inconsistencies appear.
Viewing STP Root Inconsistency
To view STP root inconsistencies in switch clouds:
Step 1
Step 2
The link and devices with root inconsistencies are displayed.
Viewing STP Type Inconsistency
To view STP type inconsistencies in switch clouds:
Step 1
Step 2
The link and devices with type inconsistencies are displayed.
STP Filters in Switch Cloud View
Spanning Tree Filter is available in Switch Cloud Maps in Topology Services. Spanning Tree information in a switch cloud provides a better picture of the Spanning Tree than displaying Spanning Tree information in the VTP domain map.
Sometimes, the Spanning Tree root might not be part of VTP domain. The availability of STP Filters on Switch Cloud View resolves this problem. When you select the filter, it displays the list of Spanning Tree Instances that are applicable to all switches in the switch cloud, in a popup dialog box.
The following information is provided for the selected Spanning Tree Instance in the Topology Map:
•
•
Viewing Spanning Tree per IEEE 802.1s Instance
You can specify the IEEE 802.1s instances by searching for the instance number. To do this:
Step 1
The Select Instance window appears.
Step 2
To view the Spanning Tree details of an IEEE 802.1s Instance in the Network Topology View window, click Select.
Viewing Spanning Tree per Cisco MISTP Instances
You can specify the MISTP instances by searching for the instance name.
To do this:
Step 1
The Select Instance window appears.
Step 2
To view the Spanning Tree details of an MISTP Instance in the Network Topology View window, click Select.
Viewing VLANs in Switch Clouds
You can specify VLANs by searching for the instance name.
Step 1
The Select VLAN window appears.
Step 2
To view the Spanning Tree details of the VLAN in the Network Topology View window, click Select.
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