Cisco Nexus 3000 series User manual

Cisco Nexus 3000 Series NX-OS Layer 2 Switching Configuration
Guide, Release 6.x
First Published: 2013-04-29
Last Modified: 2018-02-15
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Text Part Number: OL-29545-03

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CONTENTS
CHAPTER 1 New and Changed Information 1
New and Changed Information 1
CHAPTER 2 Overview 3
Layer 2 Ethernet Switching Overview 3
VLANs 3
Private VLANs 4
Spanning Tree 4
STP Overview 4
Rapid PVST+ 5
MST 5
STP Extensions 5
CHAPTER 3 Configuring VLANs 7
Information About VLANs 7
Understanding VLANs 7
VLAN Ranges 8
Creating, Deleting, and Modifying VLANs 9
About the VLAN Trunking Protocol 10
Guidelines and Limitations for VTP 10
Configuring a VLAN 11
Creating and Deleting a VLAN 11
Configuring a VLAN 12
Adding Ports to a VLAN 13
Triggering the VLAN Membership Consistency Checker 13
Configuring a VLAN as a Routed SVI 14
Configuring a VLAN as a Management SVI 15
Configuring VTP 15
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Verifying the VLAN Configuration 17
CHAPTER 4 Configuring Private VLANs 19
Information About Private VLANs 19
Primary and Secondary VLANs in Private VLANs 20
Private VLAN Ports 20
Primary, Isolated, and Community Private VLANs 21
Associating Primary and Secondary VLANs 22
Broadcast Traffic in Private VLANs 23
Private VLAN Port Isolation 23
Guidelines and Limitations for Private VLANs 23
Configuring a Private VLAN 24
Enabling Private VLANs 24
Configuring a VLAN as a Private VLAN 24
Associating Secondary VLANs with a Primary Private VLAN 25
Configuring an Interface as a Private VLAN Host Port 26
Configuring an Interface as a Private VLAN Promiscuous Port 27
Configuring a Layer 2 Interface as a Private VLAN Isolated Trunk Port 28
Configuring a Layer 2 Interface as a Private VLAN Promiscuous Trunk Port 33
Configuring VLAN Mapping for Selective Q-in-Q on a Private VLAN Secondary Trunk
Port 35
Verifying the Private VLAN Configuration 36
CHAPTER 5 Configuring Access and Trunk Interfaces 39
Information About Access and Trunk Interfaces 39
Understanding Access and Trunk Interfaces 39
Understanding IEEE 802.1Q Encapsulation 40
Understanding Access VLANs 41
Understanding the Native VLAN ID for Trunk Ports 42
Understanding Allowed VLANs 42
Understanding Native 802.1Q VLANs 42
Configuring Access and Trunk Interfaces 43
Configuring a LAN Interface as an Ethernet Access Port 43
Configuring Access Host Ports 44
Configuring Trunk Ports 44
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Configuring the Native VLAN for 802.1Q Trunking Ports 45
Configuring the Allowed VLANs for Trunking Ports 45
Configuring Native 802.1Q VLANs 46
Verifying the Interface Configuration 47
CHAPTER 6 Configuring Switching Modes 49
Information About Switching Modes 49
Guidelines and Limitations for Switching Modes 50
Licensing Requirements for Switching Modes 51
Default Settings for Switching Modes 51
Configuring Switching Modes 51
Enabling Store-and-Forward Switching 51
Reenabling Cut-Through Switching 52
CHAPTER 7 Configuring Rapid PVST+ 53
Information About Rapid PVST+ 53
Understanding STP 53
STP Overview 53
Understanding How a Topology is Created 54
Understanding the Bridge ID 54
Bridge Priority Value 54
Extended System ID 55
STP MAC Address Allocation 55
Understanding BPDUs 56
Election of the Root Bridge 57
Creating the Spanning Tree Topology 57
Understanding Rapid PVST+ 58
Rapid PVST+ Overview 58
Rapid PVST+ BPDUs 59
Proposal and Agreement Handshake 60
Protocol Timers 61
Port Roles 61
Port States 62
Rapid PVST+ Port State Overview 62
Blocking State 63
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Learning State 63
Forwarding State 63
Disabled State 64
Summary of Port States 64
Synchronization of Port Roles 64
Processing Superior BPDU Information 65
Processing Inferior BPDU Information 66
Spanning-Tree Dispute Mechanism 66
Port Cost 66
Port Priority 67
Rapid PVST+ and IEEE 802.1Q Trunks 67
Rapid PVST+ Interoperation with Legacy 802.1D STP 67
Rapid PVST+ Interoperation with 802.1s MST 68
Configuring Rapid PVST+ 68
Enabling Rapid PVST+ 68
Enabling Rapid PVST+ per VLAN 69
Configuring the Root Bridge ID 70
Configuring a Secondary Root Bridge 71
Configuring the Rapid PVST+ Port Priority 72
Configuring the Rapid PVST+ Path-Cost Method and Port Cost 73
Configuring the Rapid PVST+ Bridge Priority of a VLAN 73
Configuring the Rapid PVST+ Hello Time for a VLAN 74
Configuring the Rapid PVST+ Forward Delay Time for a VLAN 75
Configuring the Rapid PVST+ Maximum Age Time for a VLAN 75
Specifying the Link Type 75
Restarting the Protocol 76
Verifying the Rapid PVST+ Configuration 76
Triggering the VLAN STP State Consistency Checker 77
CHAPTER 8 Configuring Multiple Spanning Tree 79
Information About MST 79
MST Overview 79
MST Regions 80
MST BPDUs 80
MST Configuration Information 81
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IST, CIST, and CST 81
IST, CIST, and CST Overview 81
Spanning Tree Operation Within an MST Region 82
Spanning Tree Operations Between MST Regions 82
MST Terminology 83
Hop Count 84
Boundary Ports 84
Spanning-Tree Dispute Mechanism 85
Port Cost and Port Priority 86
Interoperability with IEEE 802.1D 86
Interoperability with Rapid PVST+: Understanding PVST Simulation 87
Configuring MST 87
MST Configuration Guidelines 87
Enabling MST 87
Entering MST Configuration Mode 88
Specifying the MST Name 89
Specifying the MST Configuration Revision Number 90
Specifying the Configuration on an MST Region 90
Mapping and Unmapping VLANs to MST Instances 92
Mapping Secondary VLANs to Same MSTI as Primary VLANs for Private VLANs 92
Configuring the Root Bridge 93
Configuring a Secondary Root Bridge 94
Configuring the Port Priority 95
Configuring the Port Cost 96
Configuring the Switch Priority 96
Configuring the Hello Time 97
Configuring the Forwarding-Delay Time 98
Configuring the Maximum-Aging Time 98
Configuring the Maximum-Hop Count 99
Configuring PVST Simulation Globally 99
Configuring PVST Simulation Per Port 100
Specifying the Link Type 101
Restarting the Protocol 101
Verifying the MST Configuration 102
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CHAPTER 9 Configuring STP Extensions 103
Information About STP Extensions 103
Overview 103
Understanding STP Port Types 103
Spanning Tree Edge Ports 104
Spanning Tree Network Ports 104
Spanning Tree Normal Ports 104
Understanding Bridge Assurance 104
Understanding BPDU Guard 105
Understanding BPDU Filtering 105
Understanding Loop Guard 106
Understanding Root Guard 107
Configuring STP Extensions 107
STP Extensions Configuration Guidelines 107
Configuring Spanning Tree Port Types Globally 108
Configuring Spanning Tree Edge Ports on Specified Interfaces 109
Configuring Spanning Tree Network Ports on Specified Interfaces 110
Enabling BPDU Guard Globally 111
Enabling BPDU Guard on Specified Interfaces 111
Enabling BPDU Filtering Globally 112
Enabling BPDU Filtering on Specified Interfaces 113
Enabling Loop Guard Globally 114
Enabling Loop Guard or Root Guard on Specified Interfaces 115
Verifying the STP Extension Configuration 116
Troubleshooting Loop Detection Error Message 116
Generating Syslog Error Messages 117
CHAPTER 10 Configuring LLDP 119
Information About Global LLDP Commands 119
Configuring LLDP 120
Information About LLDP Management TLV IP Addresses 121
Configuring LLDP Management TLV IP Addresses on an Interface 123
Configuring Interface LLDP 124
MIBs for LLDP 125
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CHAPTER 11 Configuring MAC Address Tables 127
Information About MAC Addresses 127
Guidelines for Configuring the MAC Address Tables 128
MAC Address Movement 128
Configuring MAC Addresses 128
Configuring Static MAC Addresses 128
Configuring the Aging Time for the MAC Table 129
Configuring MAC Move Loop Detection 130
Disabling MAC Address Learning on Layer 2 Interfaces 130
Clearing Dynamic Addresses from the MAC Table 131
Verifying the MAC Address Configuration 131
Triggering the Layer 2 Consistency Checker 132
CHAPTER 12 Configuring IGMP Snooping 135
Information About IGMP Snooping 135
IGMPv1 and IGMPv2 136
IGMPv3 137
IGMP Snooping Querier 137
IGMP Forwarding 137
Configuring IGMP Snooping Parameters 138
Verifying the IGMP Snooping Configuration 140
CHAPTER 13 Configuring Traffic Storm Control 143
Information About Traffic Storm Control 143
Guidelines and Limitations for Traffic Storm Control 145
Default Settings for Traffic Storm Control 146
Configuring Traffic Storm Control 146
Verifying the Traffic Storm Control Configuration 147
Traffic Storm Control Example Configuration 148
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CHAPTER 1
New and Changed Information
This chapter contains the following sections:
•New and Changed Information, page 1
New and Changed Information
This chapter contains the following sections:
Table 1: New and Changed Features
Where DocumentedAdded or
Changed
in
Release
DescriptionFeature
Information About
LLDP Management
TLV IP Addresses, on
page 121
6.0(2)U4(1)You can now send two TLVs. One for IPv4 and
the other for IPv6.
LLDP TLV
Management
Configuring LLDP
Management TLV IP
Addresses on an
Interface, on page 123
6.0(2)U3(1)You can now explicitly specify the management
IP address to be sent in the LLDP management
TLV.
This address can be one of the following:
•IP address of a port
•IP address of a VLAN (SVI)
LLDP TLV
Management
Assignment
Configuring MAC
Move Loop
Detection, on page
130
6.0(2)U3(1)You can now configure the action of bringing
down the port with the lower interface index
when a MAC address move loop is detected
between two ports.
MAC Move Threshold
Action
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Where DocumentedAdded or
Changed
in
Release
DescriptionFeature
Configuring Traffic
Storm Control, on
page 146
6.0(2)U3(1)You can configure traffic storm control to
perform the following optional corrective
actions when traffic exceeds the configured
level:
•Shut down
•Trap
Storm Control
Enhancements
•Triggering the
Layer 2
Consistency
Checker, on
page 132
•Triggering the
VLAN
Membership
Consistency
Checker, on
page 13
•Triggering the
VLAN STP
State
Consistency
Checker, on
page 77
6.0(2)U2(1)The following consistency checkers were
introduced to check for consistency and to
display the results:
•Layer 2 Consistency Checker
•VLAN Membership Consistency Checker
•VLAN STP State Consistency Checker
Consistency Checkers
Configuring IGMP
Snooping Parameters,
on page 138
6.0(2)U1(1)Added for vPCvPC
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New and Changed Information
New and Changed Information

CHAPTER 2
Overview
This chapter contains the following sections:
•Layer 2 Ethernet Switching Overview, page 3
•VLANs, page 3
•Private VLANs, page 4
•Spanning Tree , page 4
Layer 2 Ethernet Switching Overview
The device supports simultaneous, parallel connections between Layer 2 Ethernet segments. Switched
connections between Ethernet segments last only for the duration of the packet. New connections can be made
between different segments for the next packet.
The device assigns a domain (for example, a server) to each device to solve traffic congestion caused by
high-bandwidth devices and large number of users.
Because collisions cause significant congestion in Ethernet networks, an effective solution is full-duplex
communication. Typically, 10/100-Mbps Ethernet operates in half-duplex mode, which means that stations
can either receive or transmit. In full-duplex mode, which is configurable on these interfaces, two stations
can transmit and receive at the same time. When packets can flow in both directions simultaneously, the
effective Ethernet bandwidth doubles. 1/10-Gigabit Ethernet operates in full-duplex only.
VLANs
A VLAN is a switched network that is logically segmented by function, project team, or application, without
regard to the physical locations of the users. VLANs have the same attributes as physical LANs, but you can
group end stations even if they are not physically located on the same LAN segment.
Any switch port can belong to a VLAN, and unicast, broadcast, and multicast packets are forwarded and
flooded only to end stations in that VLAN. Each VLAN is considered as a logical network, and packets
destined for stations that do not belong to the VLAN must be forwarded through a bridge or a router.
All ports are assigned to the default VLAN (VLAN1) when the device comes up.
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The devices support 4094 VLANs in accordance with the IEEE 802.1Q standard. These VLANs are organized
into several ranges, and you use each range slightly differently. Some of these VLANs are reserved for internal
use by the device and are not available for configuration.
Inter-Switch Link (ISL) trunking is not supported.Note
Private VLANs
Private VLANs provide traffic separation and security at the Layer 2 level.
A private VLAN is one or more pairs of a primary VLAN and a secondary VLAN, all with the same primary
VLAN. The two types of secondary VLANs are isolated and community VLANs. Hosts on isolated VLANs
communicate only with hosts in the primary VLAN. Hosts in a community VLAN can communicate only
among themselves and with hosts in the primary VLAN but not with hosts in isolated VLANs or in other
community VLANs.
Regardless of the combination of isolated and community secondary VLANs, all interfaces within the primary
VLAN comprise one Layer 2 domain, and therefore, require only one IP subnet.
Spanning Tree
This section discusses the implementation of the Spanning Tree Protocol (STP).
STP Overview
STP provides a loop-free network at the Layer 2 level. Layer 2 LAN ports send and receive STP frames,
which are called Bridge Protocol Data Units (BPDUs), at regular intervals. Network devices do not forward
these frames but use the frames to construct a loop-free path.
802.1D is the original standard for STP, and many improvements have enhanced the basic loop-free STP.
You can create a separate loop-free path for each VLAN, which is named Per VLAN Spanning Tree (PVST+).
Additionally, the entire standard was reworked to make the loop-free convergence process faster to keep up
with the faster equipment. This STP standard with faster convergence is the 802.1w standard, which is known
as Rapid Spanning Tree (RSTP).
Finally, the 802.1s standard, Multiple Spanning Trees (MST), allows you to map multiple VLANs into a
single spanning tree instance. Each instance runs an independent spanning tree topology.
Although the software can interoperate with legacy 802.1D systems, the device runs Rapid PVST+ and MST.
You can use either Rapid PVST+ or MST in a given VDC; you cannot mix both in one VDC. Rapid PVST+
is the default STP protocol.
Cisco NX-OS uses the extended system ID and MAC address reduction; you cannot disable these features.Note
In addition, Cisco has created some proprietary features to enhance the spanning tree activities.
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Overview
Private VLANs

Rapid PVST+
Rapid PVST+ is the default spanning tree mode for the software and is enabled by default on the default
VLAN and all newly created VLANs.
A single instance, or topology, of RSTP runs on each configured VLAN, and each Rapid PVST+ instance on
a VLAN has a single root device. You can enable and disable STP on a per-VLAN basis when you are running
Rapid PVST+.
MST
The software also supports MST. The multiple independent spanning tree topologies enabled by MST provide
multiple forwarding paths for data traffic, enable load balancing, and reduce the number of STP instances
required to support a large number of VLANs.
MST incorporates RSTP, so it also allows rapid convergence. MST improves the fault tolerance of the network
because a failure in one instance (forwarding path) does not affect other instances (forwarding paths).
Changing the spanning tree mode disrupts the traffic because all spanning tree instances are stopped for
the previous mode and started for the new mode.
Note
STP Extensions
The software supports the following Cisco proprietary features:
•Spanning tree port types—The default spanning tree port type is normal. You can configure interfaces
connected to Layer 2 hosts as edge ports and interfaces connected to Layer 2 switches or bridges as
network ports.
•Bridge Assurance—Once you configure a port as a network port, Bridge Assurance sends BPDUs on
all ports and moves a port into the blocking state if it no longer receives BPDUs. This enhancement is
available only when you are running Rapid PVST+ or MST.
•BPDU Guard—BPDU Guard shuts down the port if that port receives a BPDU.
•BPDU Filter—BPDU Filter suppresses sending and receiving BPDUs on the port.
•Loop Guard—Loop guard prevents the occurrence of loop bridging because of unidirectional link failure
in a point-to-point link.
•Root Guard—Root guard prevents a port from becoming a root port or a blocked port. If you configure
a port with root guard then the port receives a superior BPDU and it immediately goes to root-inconsistent
(blocked) state.
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Overview
Rapid PVST+

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STP Extensions

CHAPTER 3
Configuring VLANs
This chapter contains the following sections:
•Information About VLANs, page 7
•Configuring a VLAN, page 11
Information About VLANs
Understanding VLANs
A VLAN is a group of end stations in a switched network that is logically segmented by function or application,
without regard to the physical locations of the users. VLANs have the same attributes as physical LANs, but
you can group end stations even if they are not physically located on the same LAN segment.
Any switch port can belong to a VLAN, and unicast, broadcast, and multicast packets are forwarded and
flooded only to end stations in that VLAN. Each VLAN is considered as a logical network, and packets
destined for stations that do not belong to the VLAN must be forwarded through a router. The following figure
shows VLANs as logical networks. The stations in the engineering department are assigned to one VLAN,
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the stations in the marketing department are assigned to another VLAN, and the stations in the accounting
department are assigned to another VLAN.
Figure 1: VLANs as Logically Defined Networks
VLANs are usually associated with IP subnetworks. For example, all the end stations in a particular IP subnet
belong to the same VLAN. To communicate between VLANs, you must route the traffic.
By default, a newly created VLAN is operational; that is, the newly created VLAN is in the no shutdown
condition. Additionally, you can configure VLANs to be in the active state, which is passing traffic, or the
suspended state, in which the VLANs are not passing packets. By default, the VLANs are in the active state
and pass traffic.
VLAN Ranges
The extended system ID is always automatically enabled in Cisco NX-OS devices.Note
The device supports up to 4094 VLANs in accordance with the IEEE 802.1Q standard. The software organizes
these VLANs into ranges, and you use each range slightly differently.
For information about configuration limits, see the configuration limits documentation for your switch.
This table describes the VLAN ranges.
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VLAN Ranges

Table 2: VLAN Ranges
UsageRangeVLANs Numbers
Cisco default. You can use this
VLAN, but you cannot modify or
delete it.
Normal1
You can create, use, modify, and
delete these VLANs.
Normal2 to 1005
You can create, name, and use
these VLANs. You cannot change
the following parameters:
•The state is always active.
•The VLAN is always
enabled. You cannot shut
down these VLANs.
Extended1006 to 3967 and 4048 to 4093
These 80 VLANs and VLAN 4094
are allocated for internal device
use. You cannot create, delete, or
modify any VLANs within the
block reserved for internal use.
Internally allocated3968 to 4047 and 4094
The software allocates a group of VLAN numbers for features such as multicast and diagnostics that need to
use internal VLANs for their operation. You cannot use, modify, or delete any of the VLANs in the reserved
group. You can display the VLANs that are allocated internally and their associated use.
Creating, Deleting, and Modifying VLANs
VLANs are numbered from 1 to 4094. All configured ports belong to the default VLAN when you first bring
up the switch. The default VLAN (VLAN1) uses only default values. You cannot create, delete, or suspend
activity in the default VLAN.
You create a VLAN by assigning a number to it. You can delete VLANs as well as move them from the active
operational state to the suspended operational state. If you attempt to create a VLAN with an existing VLAN
ID, the switch goes into the VLAN submode but does not create the same VLAN again.
Newly created VLANs remain unused until ports are assigned to the specific VLAN. All the ports are assigned
to VLAN1 by default.
Depending on the range of the VLAN, you can configure the following parameters for VLANs (except the
default VLAN):
•VLAN name
•Shutdown or not shutdown
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Configuring VLANs
Creating, Deleting, and Modifying VLANs

When you delete a specified VLAN, the ports associated to that VLAN are shut down and no traffic flows.
However, the system retains all the VLAN-to-port mapping for that VLAN, and when you reenable,or recreate,
the specified VLAN, the system automatically reinstates all the original ports to that VLAN.
Commands entered in the VLAN configuration submode are immediately executed.
VLANs 3968 to 4047 and 4094 are reserved for internal use; these VLANs cannot be changed or used.
Note
About the VLAN Trunking Protocol
VTP is a distributed VLAN database management protocol that synchronizes the VTP VLAN database across
domains. A VTP domain includes one or more network switches that share the same VTP domain name and
that are connected with trunk interfaces. Each device can be in one VTP domain, Layer 2 trunk interfaces,
and Layer 2 port channels.
Guidelines and Limitations for VTP
VTP has the following configuration guidelines and limitations:
•VLAN 1 is required on all trunk ports used for switch interconnects if VTP is supported in the network.
Disabling VLAN 1 from any of these ports prevents VTP from functioning properly.
•If you enable VTP, you must configure either version 1 or version 2.
•The show running-configuration command does not show VLAN or VTP configuration information
for VLANs 1 to 1000.
•VTP pruning is not supported.
•You must enter the copy running-config startup-config command followed by a reload after changing
a reserved VLAN range. For example:
switch(config)# system vlan 2000 reserve
This will delete all configs on vlans 2000-2127. Continue anyway? (y/n) [no] y
After the switch reload, VLANs 2000 to 2127 are reserved for internal use, which requires that you enter
the copy running-config startup-config command before the switch reload. Creating VLANs within
this range is not allowed.
•SNMP can perform GET and SET operations on the CISCO-VTP-MIB objects.
•VTP server mode and VTP client mode are not supported. The only supported mode is transparent mode,
which is the default mode.
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Configuring VLANs
About the VLAN Trunking Protocol