User's Manual
Table Of Contents
- Cisco Nexus 3000 NX-OS Layer 2 Switching Configuration Guide, Release 5.0(3)U3(1)
- Contents
- Preface
- New and Changed Information for this Release
- Overview
- Configuring Ethernet Interfaces
- Information About Ethernet Interfaces
- Configuring Ethernet Interfaces
- Configuring the UDLD Mode
- Changing an Interface Port Mode
- Configuring Interface Speed
- Disabling Link Negotiation
- Configuring the CDP Characteristics
- Enabling or Disabling CDP
- Enabling the Error-Disabled Detection
- Enabling the Error-Disabled Recovery
- Configuring the Error-Disabled Recovery Interval
- Configuring the Debounce Timer
- Configuring the Description Parameter
- Disabling and Restarting Ethernet Interfaces
- Displaying Interface Information
- Displaying Input Packet Discard Information
- Default Physical Ethernet Settings
- Configuring VLANs
- Configuring Private VLANs
- Information About Private VLANs
- Guidelines and Limitations for Private VLANs
- Configuring a Private VLAN
- Enabling Private VLANs
- Configuring a VLAN as a Private VLAN
- Associating Secondary VLANs with a Primary Private VLAN
- Configuring an Interface as a Private VLAN Host Port
- Configuring an Interface as a Private VLAN Promiscuous Port
- Configuring a Promiscuous Trunk Port
- Configuring an Isolated Trunk Port
- Configuring the Allowed VLANs for PVLAN Trunking Ports
- Configuring Native 802.1Q VLANs on Private VLANs
- Verifying the Private VLAN Configuration
- Configuring Access and Trunk Interfaces
- Configuring Switching Modes
- Configuring Rapid PVST+
- Information About Rapid PVST+
- Understanding STP
- Understanding Rapid PVST+
- Rapid PVST+ and IEEE 802.1Q Trunks
- Rapid PVST+ Interoperation with Legacy 802.1D STP
- Rapid PVST+ Interoperation with 802.1s MST
- Configuring Rapid PVST+
- Enabling Rapid PVST+
- Enabling Rapid PVST+ per VLAN
- Configuring the Root Bridge ID
- Configuring a Secondary Root Bridge
- Configuring the Rapid PVST+ Port Priority
- Configuring the Rapid PVST+ Pathcost Method and Port Cost
- Configuring the Rapid PVST+ Bridge Priority of a VLAN
- Configuring the Rapid PVST+ Hello Time for a VLAN
- Configuring the Rapid PVST+ Forward Delay Time for a VLAN
- Configuring the Rapid PVST+ Maximum Age Time for a VLAN
- Specifying the Link Type
- Restarting the Protocol
- Verifying Rapid PVST+ Configurations
- Information About Rapid PVST+
- Configuring Multiple Spanning Tree
- Information About MST
- Configuring MST
- MST Configuration Guidelines
- Enabling MST
- Entering MST Configuration Mode
- Specifying the MST Name
- Specifying the MST Configuration Revision Number
- Specifying the Configuration on an MST Region
- Mapping and Unmapping VLANs to MST Instances
- Mapping Secondary VLANs to Same MSTI as Primary VLANs for Private VLANs
- Configuring the Root Bridge
- Configuring a Secondary Root Bridge
- Configuring the Port Priority
- Configuring the Port Cost
- Configuring the Switch Priority
- Configuring the Hello Time
- Configuring the Forwarding-Delay Time
- Configuring the Maximum-Aging Time
- Configuring the Maximum-Hop Count
- Configuring PVST Simulation Globally
- Configuring PVST Simulation Per Port
- Specifying the Link Type
- Restarting the Protocol
- Verifying MST Configurations
- Configuring STP Extensions
- About STP Extensions
- Information About STP Extensions
- Configuring STP Extensions
- STP Extensions Configuration Guidelines
- Configuring Spanning Tree Port Types Globally
- Configuring Spanning Tree Edge Ports on Specified Interfaces
- Configuring Spanning Tree Network Ports on Specified Interfaces
- Enabling BPDU Guard Globally
- Enabling BPDU Guard on Specified Interfaces
- Enabling BPDU Filtering Globally
- Enabling BPDU Filtering on Specified Interfaces
- Enabling Loop Guard Globally
- Enabling Loop Guard or Root Guard on Specified Interfaces
- Verifying STP Extension Configuration
- About STP Extensions
- Configuring LLDP
- Configuring the MAC Address Table
- Configuring IGMP Snooping
- Configuring Traffic Storm Control
- INDEX
PurposeCommand or Action
Do not disable spanning tree on a VLAN unless all switches
and bridges in the VLAN have spanning tree disabled. You
cannot disable spanning tree on some of the switches and
bridges in a VLAN and leave it enabled on other switches
and bridges. This action can have unexpected results
because switches and bridges with spanning tree enabled
will have incomplete information regarding the physical
topology of the network.
Do not disable spanning tree in a VLAN without ensuring
that there are no physical loops present in the VLAN.
Spanning tree serves as a safeguard against
misconfigurations and cabling errors.
Caution
This example shows how to enable STP on a VLAN:
switch# configure terminal
switch(config)# spanning-tree vlan 5
Configuring the Root Bridge ID
The software maintains a separate instance of STP for each active VLAN in Rapid PVST+. For each VLAN,
the switch with the lowest bridge ID becomes the root bridge for that VLAN.
To configure a VLAN instance to become the root bridge, modify the bridge priority from the default value
(32768) to a significantly lower value.
When you enter the spanning-tree vlan vlan_ID root command, the switch checks the bridge priority of
the current root bridges for each VLAN. The switch sets the bridge priority for the specified VLANs to 24576
if this value will cause the switch to become the root for the specified VLANs. If any root bridge for the
specified VLANs has a bridge priority lower than 24576, the switch sets the bridge priority for the specified
VLANs to 4096 less than the lowest bridge priority.
The spanning-tree vlan vlan_ID root command fails if the value required to be the root bridge is less
than 1.
Note
The root bridge for each instance of STP should be a backbone or distribution switch. Do not configure
an access switch as the STP primary root.
Caution
Enter the diameter keyword to specify the network diameter (that is, the maximum number of bridge hops
between any two end stations in the network). When you specify the network diameter, the software
automatically selects an optimal hello time, forward delay time, and maximum age time for a network of that
diameter, which can significantly reduce the STP convergence time. You can enter the hello-time keyword
to override the automatically calculated hello time.
Cisco Nexus 3000 NX-OS Layer 2 Switching Configuration Guide, Release 5.0(3)U3(1)
80 OL-26590-01
Configuring Rapid PVST+
Configuring the Root Bridge ID