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Configuring the Root Bridge ID

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Chapter 8 Configuring Rapid PVST+ Configuring Rapid PVST+ Send feedback to [email protected] To disable Rapid PVST+ per VLAN, perform this task: Command switch(config)# no spanning-tree vlan-range Purpose Disables Rapid PVST+ on the specified VLAN; see the following Caution for information regarding this command. Caution 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 switches and bridges in a VLAN and leave it enabled on other switches and bridges in the VLAN. 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. 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. Note The spanning-tree vlan vlan_ID root command fails if the value required to be the root bridge is less than 1. Caution 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. 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. Note With the switch configured as the root bridge, do not manually configure the hello time, forward-delay time, and maximum-age time using the spanning-tree mst hello-time, spanning-tree mst forward-time, and spanning-tree mst max-age global configuration commands. OL-16597-01 Cisco Nexus 5000 Series Switch CLI Software Configuration Guide 8-19

Section	Page
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide	1
Contents	3
Preface	33
Audience	33
Organization	33
Document Conventions	34
Related Documentation	34
Obtaining Documentation and Submitting a Service Request	35
Product Overview	37
New Technologies in the Cisco Nexus 5000 Series	37
Fibre Channel over Ethernet	37
I/O Consolidation	38
Virtual Interfaces	39
Cisco Nexus 5000 Series Switch Hardware	39
Chassis	39
Expansion Modules	39
Ethernet Interfaces	39
Fibre Channel Interfaces	40
Management Interfaces	40
Cisco Nexus 5000 Series Switch Software	40
Ethernet Switching	40
FCoE and Fibre Channel Switching	41
Licensing	41
QoS	41
Serviceability	41
Switched Port Analyzer	41
Ethanalyzer	42
Call Home	42
Online Diagnostics	42
Switch Management	42
Simple Network Management Protocol	42
Role-Based Access Control	42
Configuration Methods	42
Configuring with CLI, XML Management Interface, or SNMP	43
Configuring with Cisco MDS Fabric Manager	43
Network Security Features	43
Virtual Device Contexts	43
Typical Deployment Topologies	43
Ethernet TOR Switch Topology	44
IOC Topology	45
Supported Standards	46
Configuration Fundamentals	47
Using the Command-Line Interface	49
Accessing the Command Line Interface	49
Using the CLI	50
Using CLI Command Modes	50
Changing Command Modes	51
Listing the Commands Used with Each Command Mode	51
CLI Command Hierarchy	51
EXEC Mode Commands	51
Configuration Mode Commands	53
Using Commands	54
Listing Commands and Syntax	54
Entering Command Sequences	55
Undoing or Reverting to Default Values or Conditions	55
Using Keyboard Shortcuts	55
Using CLI Variables	57
User-Defined Persistent CLI Variables	57
Using Command Aliases	58
Defining Command Aliases	58
Command Scripts	59
Executing Commands Specified in a Script	59
Using CLI Variables in Scripts	60
Setting the Delay Time	61
Configuring the Switch	63
Image Files on the Switch	63
Starting the Switch	64
Boot Sequence	64
Console Settings	65
Upgrading the Switch	66
Upgrade Procedure Summary	66
Detailed Upgrade Procedure	66
Downgrading from a Higher Release	68
Initial Configuration	69
Configuration Prerequisites	69
Initial Setup	70
Preparing to Configure the Switch	70
Default Login	71
Configuring the Switch	71
Changing the Initial Configuration	74
Accessing the Switch	74
Additional Switch Configuration	75
Assigning a Switch Name	75
Configuring Date, Time, and Time Zone	75
Adjusting for Daylight Saving Time or Summer Time	76
NTP Configuration	77
About NTP	77
NTP Configuration Guidelines	78
Configuring NTP	79
NTP CFS Distribution	79
Enabling NTP Distribution	80
Committing NTP Configuration Changes	80
Discarding NTP Configuration Changes	80
Releasing Fabric Session Lock	81
Database Merge Guidelines	81
NTP Session Status Verification	81
Management Interface Configuration	81
About the mgmt0 Interface	82
Configuring the Management Interface	82
Displaying Management Interface Configuration	82
Shutting Down the Management Interface	83
Managing the Switch Configuration	83
Displaying the Switch Configuration	83
Saving a Configuration	84
Clearing a Configuration	84
Using Switch File Systems	84
Setting the Current Directory	84
Displaying the Current Directory	85
Listing the Files in a Directory	85
Creating a Directory	85
Deleting an Existing Directory	85
Moving Files	86
Copying Files	86
Deleting Files	86
Displaying File Contents	87
Displaying File Checksums	87
Saving Command Output to a File	87
Compressing and Uncompressing Files	87
Managing Licenses	89
Licensing Terminology	89
Licensing Model	90
License Installation	91
Obtaining a Factory-Installed License	91
Performing a Manual Installation	92
Obtaining the License Key File	92
Installing the License Key File	92
Backing Up License Files	94
Identifying License Features in Use	94
Uninstalling Licenses	94
Updating Licenses	96
Grace Period Alerts	96
License Transfers Between Switches	97
Verifying the License Configuration	98
LAN Switching	99
Configuring Ethernet Interfaces	101
Information About Ethernet Interfaces	101
About the Interface Command	101
About the Unidirectional Link Detection Parameter	102
UDLD Overview	102
Default UDLD Configuration	103
UDLD Aggressive and Nonaggressive Modes	103
About Interface Speed	104
About the Cisco Discovery Protocol	104
Default CDP Configuration	104
About the Debounce Timer Parameters	104
About MTU Configuration	105
Configuring Ethernet Interfaces	105
Configuring the UDLD Mode	105
Configuring Interface Speed	106
Configuring the Cisco Discovery Protocol	107
Configuring the CDP Characteristics	107
Enabling or Disabling CDP	108
Configuring the Debounce Timer	108
Configuring the Description Parameter	109
Disabling and Restarting Ethernet Interfaces	109
Displaying Interface Information	110
Default Physical Ethernet Settings	112
Configuring VLANs	115
Information About VLANs	115
Understanding VLANs	115
Understanding VLAN Ranges	116
Creating, Deleting, and Modifying VLANs	117
Configuring a VLAN	118
Creating and Deleting a VLAN	118
Entering the VLAN Submode and Configuring the VLAN	119
Adding Ports to a VLAN	120
Verifying VLAN Configuration	120
Configuring Private VLANs	123
About Private VLANs	123
Primary and Secondary VLANs in Private VLANs	124
Understanding Private VLAN Ports	125
Understanding Primary, Isolated, and Community Private VLANs	125
Associating Primary and Secondary VLANs	126
Understanding Broadcast Traffic in Private VLANs	127
Understanding Private VLAN Port Isolation	127
Configuring a Private VLAN	127
Configuration Guidelines for Private VLANs	128
Enabling Private VLANs	128
Configuring a VLAN as a Private VLAN	129
Associating Secondary VLANs with a Primary Private VLAN	129
Configuring an Interface as a Private VLAN Host Port	130
Configuring an Interface as a Private VLAN Promiscuous Port	131
Verifying Private VLAN Configuration	132
Configuring Rapid PVST+	135
Information About Rapid PVST+	135
Understanding STP	136
Overview	136
Understanding How a Topology is Created	136
Understanding the Bridge ID	137
Bridge Priority Value	137
Extended System ID	137
STP MAC Address Allocation	138
Understanding BPDUs	138
Election of the Root Bridge	139
Creating the Spanning Tree Topology	139
Understanding Rapid PVST+	140
Overview	140
Rapid PVST+ BPDUs	142
Proposal and Agreement Handshake	142
Protocol Timers	143
Port Roles	144
Port States	145
Rapid PVST+ Port State Overview	145
Blocking State	146
Learning State	146
Forwarding State	146
Disabled State	147
Summary of Port States	147
Synchronization of Port Roles	147
Processing Superior BPDU Information	148
Processing Inferior BPDU Information	148
Detecting Unidirectional Link Failure	148
Port Cost	149
Port Priority	150
Rapid PVST+ and IEEE 802.1Q Trunks	150
Rapid PVST+ Interoperation with Legacy 802.1D STP	150
Rapid PVST+ Interoperation with 802.1s MST	151
Configuring Rapid PVST+	151
Enabling Rapid PVST+	151
Enabling Rapid PVST+ per VLAN	152
Configuring the Root Bridge ID	153
Configuring a Secondary Root Bridge	154
Configuring the Rapid PVST+ Port Priority	155
Configuring the Rapid PVST+ Pathcost Method and Port Cost	155
Configuring the Rapid PVST+ Bridge Priority of a VLAN	156
Configuring the Rapid PVST+ Hello Time for a VLAN	157
Configuring the Rapid PVST+ Forward Delay Time for a VLAN	157
Configuring the Rapid PVST+ Maximum Age Time for a VLAN	157
Specifying the Link Type	158
Restarting the Protocol	159
Verifying Rapid PVST+ Configurations	159
Configuring MST	161
Information About MST	161
MST Overview	162
MST Regions	162
MST BPDUs	163
MST Configuration Information	163
IST, CIST, and CST	164
IST, CIST, and CST Overview	164
Spanning Tree Operation Within an MST Region	165
Spanning Tree Operations Between MST Regions	165
MST Terminology	166
Hop Count	167
Boundary Ports	167
Detecting Unidirectional Link Failure	168
Port Cost and Port Priority	168
Interoperability with IEEE 802.1D	169
Interoperability with Rapid PVST+: Understanding PVST Simulation	169
Configuring MST	169
MST Configuration Guidelines	170
Enabling MST	170
Entering MST Configuration Mode	171
Specifying the MST Name	172
Specifying the MST Configuration Revision Number	173
Specifying the Configuration on an MST Region	173
Mapping and Unmapping VLANs to MST Instances	175
Mapping Secondary VLANs to Same MSTI as Primary VLANs for Private VLANs	176
Configuring the Root Bridge	176
Configuring a Secondary Root Bridge	177
Configuring the Port Priority	178
Configuring the Port Cost	179
Configuring the Switch Priority	180
Configuring the Hello Time	181
Configuring the Forwarding-Delay Time	182
Configuring the Maximum-Aging Time	182
Configuring the Maximum-Hop Count	182
Configuring PVST Simulation Globally	183
Configuring PVST Simulation Per Port	183
Specifying the Link Type	184
Restarting the Protocol	185
Verifying MST Configurations	185
Configuring STP Extensions	187
Information About STP Extensions	187
Understanding STP Port Types	188
Spanning Tree Edge Ports	188
Spanning Tree Network Ports	188
Spanning Tree Normal Ports	188
Understanding Bridge Assurance	188
Understanding BPDU Guard	189
Understanding BPDU Filtering	189
Understanding Loop Guard	190
Understanding Root Guard	191
Configuring STP Extensions	191
STP Extensions Configuration Guidelines	191
Configuring Spanning Tree Port Types Globally	192
Configuring Spanning Tree Edge Ports on Specified Interfaces	193
Configuring Spanning Tree Network Ports on Specified Interfaces	193
Enabling BPDU Guard Globally	194
Enabling BPDU Guard on Specified Interfaces	195
Enabling BPDU Filtering Globally	196
Enabling BPDU Filtering on Specified Interfaces	196
Enabling Loop Guard Globally	198
Enabling Loop Guard or Root Guard on Specified Interfaces	198
Verifying STP Extension Configuration	199
Configuring Port Channels	201
Information About Port Channels	201
Understanding Port Channels	201
Compatibility Requirements	202
Load Balancing Using Port Channels	203
Understanding LACP	204
LACP Overview	205
LACP ID Parameters	205
Port-Channel Modes	206
LACP Marker Responders	207
LACP-Enabled and Static Port Channels Differences	207
Configuring Port Channels	207
Creating a Port Channel	207
Adding a Port to a Port Channel	208
Configuring Load Balancing Using Port Channels	209
Enabling LACP	210
Configuring Port-Channel Port Modes	210
Configuring the LACP System Priority and System ID	211
Configuring the LACP Port Priority	211
Verifying Port-Channel Configuration	212
Configuring Access and Trunk Interfaces	213
Information About Access and Trunk Interfaces	213
Understanding Access and Trunk Interfaces	213
Understanding IEEE 802.1Q Encapsulation	214
Understanding Access VLANs	215
Understanding the Native VLAN ID for Trunk Ports	215
Understanding Allowed VLANs	216
Configuring Access and Trunk Interfaces	216
Configuring a LAN Interface as an Ethernet Access Port	216
Configuring Access Host Ports	217
Configuring Trunk Ports	218
Configuring the Native VLAN for 802.1Q Trunking Ports	218
Configuring the Allowed VLANs for Trunking Ports	219
Verifying Interface Configuration	220
Configuring the MAC Address Table	221
Information About MAC Addresses	221
Configuring MAC Addresses	221
Configuring a Static MAC Address	222
Configuring the Aging Time for the MAC Table	222
Clearing Dynamic Addresses from the MAC Table	223
Verifying the MAC Address Configuration	223
Configuring IGMP Snooping	225
Information About IGMP Snooping	225
IGMPv1 and IGMPv2	226
IGMPv3	227
IGMP Snooping Querier	227
IGMP Forwarding	227
Configuring IGMP Snooping Parameters	228
Verifying IGMP Snooping Configuration	230
Configuring Traffic Storm Control	233
Information About Traffic Storm Control	233
Guidelines and Limitations	234
Configuring Traffic Storm Control	235
Verifying Traffic Storm Control Configuration	235
Displaying Traffic Storm Control Counters	235
Traffic Storm Control Example Configuration	236
Default Settings	236
Switch Security Features	237
Configuring AAA	239
Information About AAA	239
AAA Security Services	239
Benefits of Using AAA	240
Remote AAA Services	240
AAA Server Groups	241
AAA Service Configuration Options	241
Authentication and Authorization Process for User Login	242
Prerequisites for Remote AAA	243
AAA Guidelines and Limitations	244
Configuring AAA	244
Configuring Console Login Authentication Methods	244
Configuring Default Login Authentication Methods	246
Enabling Login Authentication Failure Messages	246
Enabling MSCHAP Authentication	247
Configuring AAA Accounting Default Methods	248
Using AAA Server VSAs with Nexus 5000 Series Switches	249
About VSAs	249
VSA Format	249
Specifying Cisco Nexus 5000 Series Switch User Roles and SMNPv3 Parameters on AAA Servers	249
Displaying and Clearing the Local AAA Accounting Log	250
Verifying AAA Configuration	250
Example AAA Configuration	250
Default Settings	251
Configuring RADIUS	253
Information About RADIUS	253
RADIUS Network Environments	253
RADIUS Operation	254
RADIUS Server Monitoring	255
Vendor-Specific Attributes	255
Prerequisites for RADIUS	256
Guidelines and Limitations	256
Configuring RADIUS Servers	256
Configuring RADIUS Server Hosts	257
Configuring Global Preshared Keys	258
Configuring RADIUS Server Preshared Keys	258
Configuring RADIUS Server Groups	259
Allowing Users to Specify a RADIUS Server at Login	260
Configuring the Global RADIUS Transmission Retry Count and Timeout Interval	261
Configuring the RADIUS Transmission Retry Count and Timeout Interval for a Server	261
Configuring Accounting and Authentication Attributes for RADIUS Servers	262
Configuring Periodic RADIUS Server Monitoring	263
Configuring the Dead-Time Interval	264
Manually Monitoring RADIUS Servers or Groups	265
Verifying RADIUS Configuration	265
Displaying RADIUS Server Statistics	265
Example RADIUS Configuration	266
Default Settings	266
Configuring TACACS+	267
Information About TACACS+	267
TACACS+ Advantages	268
User Login with TACACS+	268
Default TACACS+ Server Encryption Type and Preshared Key	269
TACACS+ Server Monitoring	269
Prerequisites for TACACS+	270
Guidelines and Limitations	270
Configuring TACACS+	270
TACACS+ Server Configuration Process	270
Enabling TACACS+	271
Configuring TACACS+ Server Hosts	271
Configuring Global Preshared Keys	272
Configuring TACACS+ Server Preshared Keys	273
Configuring TACACS+ Server Groups	273
Specifying a TACACS+ Server at Login	274
Configuring the Global TACACS+ Timeout Interval	275
Configuring the Timeout Interval for a Server	275
Configuring TCP Ports	276
Configuring Periodic TACACS+ Server Monitoring	277
Configuring the Dead-Time Interval	278
Manually Monitoring TACACS+ Servers or Groups	278
Disabling TACACS+	278
Displaying TACACS+ Statistics	279
Verifying TACACS+ Configuration	279
Example TACACS+ Configuration	279
Default Settings	280
Configuring SSH and Telnet	281
Information About SSH and Telnet	281
SSH Server	281
SSH Client	282
SSH Server Keys	282
Telnet Server	282
Prerequisites for SSH	282
Guidelines and Limitations	283
Configuring SSH	283
Generating SSH Server Keys	283
Specifying the SSH Public Keys for User Accounts	284
Specifying the SSH Public Keys in Open SSH Format	284
Specifying the SSH Public Keys in IETF SECSH Format	284
Specifying the SSH Public Keys in PEM-Formatted Public Key Certificate Form	285
Starting SSH Sessions to Remote Devices	286
Clearing SSH Hosts	286
Disabling the SSH Server	286
Deleting SSH Server Keys	286
Clearing SSH Sessions	287
Configuring Telnet	287
Enabling the Telnet Server	287
Starting Telnet Sessions to Remote Devices	288
Clearing Telnet Sessions	288
Verifying the SSH and Telnet Configuration	289
SSH Example Configuration	289
Default Settings	290
Configuring ACLs	291
Information About ACLs	291
IP ACL Types and Applications	291
Application Order	292
Rules	292
Source and Destination	292
Protocols	292
Implicit Rules	293
Additional Filtering Options	293
Sequence Numbers	293
Logical Operators and Logical Operation Units	294
Configuring IP ACLs	294
Creating an IP ACL	295
Changing an IP ACL	295
Removing an IP ACL	296
Changing Sequence Numbers in an IP ACL	297
Applying an IP ACL as a Port ACL	297
Applying an IP ACL as a VACL	298
Verifying IP ACL Configurations	298
Displaying and Clearing IP ACL Statistics	299
Configuring MAC ACLs	299
Creating a MAC ACL	300
Changing a MAC ACL	300
Removing a MAC ACL	301
Changing Sequence Numbers in a MAC ACL	302
Applying a MAC ACL as a Port ACL	302
Applying a MAC ACL as a VACL	303
Verifying MAC ACL Configurations	303
Displaying and Clearing MAC ACL Statistics	303
Information About VLAN ACLs	304
VACLs and Access Maps	304
VACLs and Actions	304
Statistics	305
Configuring VACLs	305
Creating or Changing a VACL	305
Removing a VACL	306
Applying a VACL to a VLAN	306
Verifying VACL Configuration	307
Displaying and Clearing VACL Statistics	307
Default Settings	308
System Management	309
Using Cisco Fabric Services	311
Information About CFS	311
CFS Distribution	312
CFS Distribution Modes	312
Uncoordinated Distribution	313
Coordinated Distribution	313

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8-19

Cisco Nexus 5000 Series Switch CLI Software Configuration Guide

OL-16597-01

Chapter 8

Configuring Rapid PVST+

To disable Rapid PVST+ per VLAN, perform this task:

Caution

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 switches and bridges in a VLAN and leave it

enabled on other switches and bridges in the VLAN. 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.

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.

Note

The

spanning-tree vlan

vlan_ID

root

command fails if the value required to be the root bridge is less

than 1.

Caution

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.

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.

Note

With the switch configured as the root bridge, do not manually configure the hello time, forward-delay

time, and maximum-age time using the

spanning-tree mst hello-time

spanning-tree mst

forward-time

, and

spanning-tree mst max-age

global configuration commands.

Command

Purpose

switch(config)#

no spanning-tree

vlan-range

Disables Rapid PVST+ on the specified VLAN; see the

following Caution for information regarding this

command.