Configuring Layer 2 Interfaces

This chapter describes how to configure Layer 2 switching ports as access or trunk ports on Cisco NX-OS devices.


Note

A Layer 2 port can function as either one of the following:

  • A trunk port

  • An access port

Note

See the System Management Overview for information about configuring a SPAN destination interface.

You can configure Layer 2 switching ports as access or trunk ports. Trunks carry the traffic of multiple VLANs over a single link and allow you to extend VLANs across an entire network. All Layer 2 switching ports maintain media access control (MAC) address tables.


Note

See the Layer 2 Switching Configuration Guide for information about VLANs, MAC address tables, private VLANs, and the Spanning Tree Protocol.

Information About Access and Trunk Interfaces


Note

The device supports only IEEE 802.1Q-type VLAN trunk encapsulation.

About Access and Trunk Interfaces

A Layer 2 port can be configured as an access or a trunk port as follows:

  • An access port can have only one VLAN configured on that port; it can carry traffic for only one VLAN.

  • A trunk port can have two or more VLANs configured on that port; it can carry traffic for several VLANs simultaneously.

By default, all the ports on the Cisco Nexus® 3550-T switches are Layer 3 ports/Layer 2 ports.

You can make all ports Layer 2 ports using the setup script or by entering the system default switchport command. See the Cisco Nexus® 3550-T Fundamentals Configuration section for information about using the setup script. To configure the port as a Layer 2 port using the CLI, use the switchport command.

The following figure shows how you can use trunk ports in the network. The trunk port carries traffic for two or more VLANs.

Figure 1. Trunk and Access Ports and VLAN Traffic



Note

See the Cisco Nexus® 3550-T Layer 2 Switching Configuration section for information about VLANs.

In order to correctly deliver the traffic on a trunk port with several VLANs, the device uses the IEEE 802.1Q encapsulation, or tagging, method (see the “IEEE 802.1Q Encapsulation” section for more information).

To optimize the performance on access ports, you can configure the port as a host port. Once the port is configured as a host port, it is automatically set as an access port, and channel grouping is disabled. Use the host designation to decrease the time that it takes the designated port to begin to forward packets.

Only an end station can be set as a host port; you will receive an error message if you attempt to configure other ports as hosts.

If an access port receives a packet with an 802.1Q tag in the header other than the access VLAN value, that port drops the packet without learning its MAC source address.

A Layer 2 interface can function as either an access port or a trunk port; it cannot function as both port types simultaneously.

When you change a Layer 2 interface back to a Layer 3 interface, that interface loses all the Layer 2 configuration and resumes the default VLAN configurations.

IEEE 802.1Q Encapsulation


Note

For information about VLANs, see the Cisco Nexus® 3550-T Layer 2 Switching Configuration section.

A trunk is a point-to-point link between the switch and another networking device. Trunks carry the traffic of multiple VLANs over a single link and allow you to extend VLANs across an entire network.

To correctly deliver the traffic on a trunk port with several VLANs, the device uses the IEEE 802.1Q encapsulation, or tagging, method that uses a tag that is inserted into the frame header. This tag carries information about the specific VLAN to which the frame and packet belong. This method allows packets that are encapsulated for several different VLANs to traverse the same port and maintain traffic separation between the VLANs. Also, the encapsulated VLAN tag allows the trunk to move traffic end-to-end through the network on the same VLAN.

Figure 2. Header Without and With 802.1Q Tag


Access VLANs

When you configure a port in access mode, you can specify which VLAN will carry the traffic for that interface. If you do not configure the VLAN for a port in access mode, or an access port, the interface carries traffic for the default VLAN (VLAN1).

You can change the access port membership in a VLAN by specifying the new VLAN. You must create the VLAN before you can assign it as an access VLAN for an access port. If you change the access VLAN on an access port to a VLAN that is not yet created, the system shuts that access port down.

If an access port receives a packet with an 802.1Q tag in the header other than the access VLAN value, that port drops the packet without learning its MAC source address.

Native VLAN IDs for Trunk Ports

A trunk port can carry nontagged packets simultaneously with the 802.1Q tagged packets. When you assign a default port VLAN ID to the trunk port, all untagged traffic travels on the default port VLAN ID for the trunk port, and all untagged traffic is assumed to belong to this VLAN. This VLAN is referred to as the native VLAN ID for a trunk port. That is, the native VLAN ID is the VLAN that carries untagged traffic on trunk ports.


Note

Native VLAN ID numbers must match on both ends of the trunk.

The trunk port sends an egressing packet with a VLAN that is equal to the default port VLAN ID as untagged; all the other egressing packets are tagged by the trunk port. If you do not configure a native VLAN ID, the trunk port uses the default VLAN.

Tagging Native VLAN Traffic

The Cisco software supports the IEEE 802.1Q standard on trunk ports. In order to pass untagged traffic through the trunk ports, you must create a VLAN that does not tag any packets (or you can use the default VLAN). Untagged packets can pass through trunk ports and access ports.

However, all packets that enter the device with an 802.1Q tag that matches the value of the native VLAN on the trunk are stripped of any tagging and egress the trunk port as untagged packets. This situation can cause problems because you may want to retain the tagging on packets on the native VLAN for the trunk port.

Allowed VLANs

By default, a trunk port sends traffic to and receives traffic from all VLANs. All VLAN IDs are allowed on each trunk. However, you can remove VLANs from this inclusive list to prevent traffic from the specified VLANs from passing over the trunk. Later, you can add any specific VLANs that you may want the trunk to carry traffic for back to the list.

To partition the Spanning Tree Protocol (STP) topology for the default VLAN, you can remove VLAN1 from the list of allowed VLANs. Otherwise, VLAN1, which is enabled on all ports by default, will have a very big STP topology, which can result in problems during STP convergence. When you remove VLAN1, all data traffic for VLAN1 on this port is blocked, but the control traffic continues to move on the port.


Note

See the Cisco Nexus® 3550-T Layer 2 Switching Configuration section for more information about STP.

Default Interfaces

You can use the default interface feature to clear the configured parameters for both physical and logical interfaces such as the Ethernet, loopback, VLAN network, and the port-channel interface.


Note

All 48 ports can be selected for the default interface.

Switch Virtual Interface and Autostate Behavior

In Cisco NX-OS, a switch virtual interface (SVI) represents a logical interface between the bridging function and the routing function of a VLAN in the device.

The operational state of this interface is governed by the state of the various ports in its corresponding VLAN. An SVI interface on a VLAN comes up when at least one port in that VLAN is in the Spanning Tree Protocol (STP) forwarding state. Similarly, this interface goes down when the last STP forwarding port goes down or goes to another STP state.

High Availability

The software supports high availability for Layer 2 ports.


Note

See the Cisco Nexus® 3550-T High Availability and Redundancy Guide for complete information about high availability features.

Prerequisites for Layer 2 Interfaces

Layer 2 interfaces have the following prerequisites:

  • You are logged onto the device.

  • By default, Cisco NX-OS configures Layer 3 parameters. If you want to configure Layer 2 parameters, you need to switch the port mode to Layer 2. You can change the port mode by using the switchport command.

  • You must configure the port as a Layer 2 port before you can use the switchport mode command. By default, all ports on the device are Layer 3 ports. By default, all ports on the Cisco Nexus® 3550-T devices are Layer 2 ports.

Guidelines and Limitations for Layer 2 Interfaces

VLAN trunking has the following configuration guidelines and limitations:

  • A port can be either a Layer 2 or a Layer 3 interface; it cannot be both simultaneously.

  • When you change a Layer 3 port to a Layer 2 port or a Layer 2 port to a Layer 3 port, all layer-dependent configuration is lost. When you change an access or trunk port to a Layer 3 port, all information about the access VLAN, native VLAN, allowed VLANs, and so forth, is lost.

  • Do not connect devices with access links because access links may partition a VLAN.

  • When connecting Cisco devices through an 802.1Q trunk, make sure that the native VLAN for an 802.1Q trunk is the same on both ends of the trunk link. If the native VLAN on one end of the trunk is different from the native VLAN on the other end, spanning tree loops might result.

  • Disabling spanning tree on the native VLAN of an 802.1Q trunk without disabling spanning tree on every VLAN in the network can cause spanning tree loops. You must leave spanning tree enabled on the native VLAN of an 802.1Q trunk. If you cannot leave spanning tree enabled, you must disable spanning tree on every VLAN in the network. Make sure that your network has no physical loops before you disable spanning tree.

  • When you connect two Cisco devices through 802.1Q trunks, the devices exchange spanning tree bridge protocol data units (BPDUs) on each VLAN allowed on the trunks. The BPDUs on the native VLAN of the trunk are sent untagged to the reserved IEEE 802.1D spanning tree multicast MAC address (01-80-C2-00-00-00). The BPDUs on all other VLANs on the trunk are sent tagged to the reserved Cisco Shared Spanning Tree (SSTP) multicast MAC address (01-00-0c-cc-cc-cd).

  • Non-Cisco 802.1Q devices maintain only a single instance of spanning tree (the Mono Spanning Tree) that defines the spanning tree topology for all VLANs. When you connect a Cisco switch to a non-Cisco switch through an 802.1Q trunk, the Mono Spanning Tree of the non-Cisco switch and the native VLAN spanning tree of the Cisco switch combine to form a single spanning tree topology known as the Common Spanning Tree (CST).

  • Because Cisco devices transmit BPDUs to the SSTP multicast MAC address on VLANs other than the native VLAN of the trunk, non-Cisco devices do not recognize these frames as BPDUs and flood them on all ports in the corresponding VLAN. Other Cisco devices connected to the non-Cisco 802.1Q cloud receive these flooded BPDUs. This BPDU reception allows Cisco switches to maintain a per-VLAN spanning tree topology across a cloud of non-Cisco 802.1Q devices. The non-Cisco 802.1Q cloud that separates the Cisco devices is treated as a single broadcast segment between all devices connected to the non-Cisco 802.1Q cloud through 802.1Q trunks.

  • Make certain that the native VLAN is the same on all of the 802.1Q trunks that connect the Cisco devices to the non-Cisco 802.1Q cloud.

  • If you are connecting multiple Cisco devices to a non-Cisco 802.1Q cloud, all of the connections must be through 802.1Q trunks. You cannot connect Cisco devices to a non-Cisco 802.1Q cloud through access ports because doing so places the access port on the Cisco device into the spanning tree “port inconsistent” state and no traffic will pass through the port.

  • You can group trunk ports into port-channel groups, but all trunks in the group must have the same configuration. When a group is first created, all ports follow the parameters set for the first port to be added to the group. If you change the configuration of one of these parameters, the device propagates that setting to all ports in the group, such as the allowed VLANs and the trunk status. For example, if one port in a port group ceases to be a trunk, all ports cease to be trunks.

  • When MAC addresses are cleared on a VLAN with the clear mac address-table dynamic command, the dynamic ARP (Address Resolution Protocol) entries on that VLAN are refreshed.

  • If a static ARP entry exists on the VLAN and no MAC address to port mapping is present, the supervisor may generate an ARP request to learn the MAC address. Upon learning the MAC address, the adjacency entry points to the correct physical port.

  • Cisco NX-OS does not support transparent bridging between two VLANs when one of the SVIs is on the Cisco Nexus 9000 using the BIA MAC (burned-in MAC address). This occurs when the BIA MAC is shared between SVIs/VLANs. A MAC, different from the BIA MAC, can be configured under the SVI for transparent bridging to work properly.

  • You may get an error message when you attempt to configure the interface mode to trunk and trunk VLANs simultaneously. On Cisco NX-OS interfaces, the default value of interface mode is access. To implement any trunk related configurations, you must first change the interface mode to trunk and then configure the trunk VLAN ranges.

  • Cisco Nexus 3550-T - 10.1(2t) release switch does cut-through forwarding; hence there is no MTU- check implemented.

    Hardware buffering is not designed for jumbo packets and packets beyond regular mtu size 1516 is not supported.

Default Settings for Layer 2 Interfaces

The following table lists the default settings for device access and trunk port mode parameters.

Configuring Access and Trunk Interfaces


Note

If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature might differ from the Cisco IOS commands that you would use.

Configuring a VLAN Interface as a Layer 2 Access Port

You can configure a Layer 2 port as an access port. An access port transmits packets on only one, untagged VLAN. You specify which VLAN traffic that the interface carries, which becomes the access VLAN. If you do not specify a VLAN for an access port, that interface carries traffic only on the default VLAN. The default VLAN is VLAN1.

The VLAN must exist before you can specify that VLAN as an access VLAN. The system shuts down an access port that is assigned to an access VLAN that does not exist.

Before you begin

Ensure that you are configuring a Layer 2 interface.

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

interface ethernet {{type slot/port} | {port-channel number}}

Example:

switch(config)# interface ethernet 1/1
switch(config-if)#

Specifies an interface to configure, and enters interface configuration mode.

Step 3

switchport mode [access | trunk]

Example:

switch(config-if)# switchport mode access

Sets the interface as a nontrunking nontagged, single-VLAN Layer 2 interface. An access port can carry traffic in one VLAN only. By default, an access port carries traffic for VLAN1; to set the access port to carry traffic for a different VLAN, use the switchport access vlan command.

Step 4

switchport access vlan vlan-id

Example:

switch(config-if)# switchport access vlan 5

Specifies the VLAN for which this access port will carry traffic. If you do not enter this command, the access port carries traffic on VLAN1 only; use this command to change the VLAN for which the access port carries traffic.

Step 5

exit

Example:

switch(config-if)# exit
switch(config)#

Exits the interface configuration mode.

Step 6

show interface

Example:

switch# show interface

(Optional) Displays the interface status and information.

Step 7

no shutdown

Example:

switch# configure terminal
switch(config)# int e1/1
switch(config-if)# no shutdown

(Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

Step 8

copy running-config startup-config

Example:

switch(config)# copy running-config startup-config

(Optional) Copies the running configuration to the startup configuration.

Example

This example shows how to set Ethernet 1/1 as a Layer 2 access port that carries traffic for VLAN 5 only: 

switch# configure terminal 
switch(config)# interface ethernet 1/1
switch(config-if)# switchport mode access
switch(config-if)# switchport access vlan 5
switch(config-if)#

Configuring Access Host Ports


Note

You should apply the switchport host command only to interfaces that are connected to an end station.

You can optimize the performance of access ports that are connected to end stations by simultaneously setting that port as an access port. An access host port handles the STP like an edge port and immediately moves to the forwarding state without passing through the blocking and learning states. Configuring an interface as an access host port also disables port channeling on that interface.


Note

See the Configuring Port Channels and the Cisco Nexus® 3550-T Layer 2 Switching Configuration sections for information about port-channel interfaces

Before you begin

Ensure that you are configuring the correct interface to an interface that is an end station.

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

interface ethernet type slot/port

Example:

switch(config)# interface ethernet 1/1
switch(config-if)#

Specifies an interface to configure, and enters interface configuration mode.

Step 3

switchport host

Example:

switch(config-if)# switchport host

Sets the interface to be an access host port, which immediately moves to the spanning tree forwarding state and disables port channeling on this interface.

Note

 

Apply this command only to end stations.

Step 4

exit

Example:

switch(config-if-range)# exit
switch(config)#

Exits the interface mode.

Step 5

show interface

Example:

switch# show interface

(Optional) Displays the interface status and information.

Step 6

no shutdown

Example:

switch# configure terminal
switch(config)# int e1/1
switch(config-if)# no shutdown

(Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

Step 7

copy running-config startup-config

Example:

switch(config)# copy running-config startup-config

(Optional) Copies the running configuration to the startup configuration.

Example

This example shows how to set Ethernet 1/1 as a Layer 2 access port with PortFast enabled and port channel disabled: 

switch# configure terminal 
switch(config)# interface ethernet 1/1
switch(config-if)# switchport host
switch(config-if)#

Configuring Trunk Ports

You can configure a Layer 2 port as a trunk port. A trunk port transmits untagged packets for one VLAN plus encapsulated, tagged, packets for multiple VLANs. (See the IEEE 802.1Q Encapsulation section for information about encapsulation.)


Note

The device supports 802.1Q encapsulation only.

Before you begin

Before you configure a trunk port, ensure that you are configuring a Layer 2 interface.

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

interface {type slot/port | port-channel number}

Example:

switch(config)# interface ethernet 1/1
switch(config-if)#

Specifies an interface to configure, and enters interface configuration mode.

Step 3

switchport mode [access | trunk]

Example:

switch(config-if)# switchport mode trunk

Sets the interface as a Layer 2 trunk port. A trunk port can carry traffic in one or more VLANs on the same physical link (VLANs are based on the trunk-allowed VLANs list). By default, a trunk interface can carry traffic for all VLANs. To specify that only certain VLANs are allowed on the specified trunk, use the switchport trunk allowed vlan command.

Step 4

exit

Example:

switch(config-if)# exit
switch(config)#

Exits the interface mode.

Step 5

show interface

Example:

switch# show interface

(Optional) Displays the interface status and information.

Step 6

no shutdown

Example:

switch# configure terminal
switch(config)# int e1/1
switch(config-if)# no shutdown

(Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

Step 7

copy running-config startup-config

Example:

switch(config)# copy running-config startup-config

(Optional) Copies the running configuration to the startup configuration.

Example

This example shows how to set Ethernet 1/1 as a Layer 2 trunk port: 

switch# configure terminal 
switch(config)# interface ethernet 1/1
switch(config-if)# switchport mode trunk
switch(config-if)#

Configuring the Native VLAN for 802.1Q Trunking Ports

You can configure the native VLAN for 802.1Q trunk ports. If you do not configure this parameter, the trunk port uses the default VLAN as the native VLAN ID.

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

interface {{type slot/port} | {port-channel number}}

Example:

switch(config)# interface ethernet 1/1
switch(config-if)#

Specifies an interface to configure, and enters interface configuration mode.

Step 3

switchport trunk native vlan vlan-id

Example:

switch(config-if)# switchport trunk native vlan 5

Sets the native VLAN for the 802.1Q trunk. Valid values are from 1 to 4094, except those VLANs reserved for internal use. The default value is VLAN1.

Step 4

exit

Example:

switch(config-if-range)# exit
switch(config)#

Exits interface configuration mode.

Step 5

show vlan

Example:

switch# show vlan

(Optional) Displays the status and information of VLANs.

Step 6

no shutdown

Example:

switch# configure terminal
switch(config)# int e1/1
switch(config-if)# no shutdown

(Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

Step 7

copy running-config startup-config

Example:

switch(config)# copy running-config startup-config

(Optional) Copies the running configuration to the startup configuration.

Example

This example shows how to set the native VLAN for the Ethernet 1/1, Layer 2 trunk port to VLAN 5: 

switch# configure terminal 
switch(config)# interface ethernet 1/1
switch(config-if)# switchport trunk native vlan 5
switch(config-if)#

Configuring the Allowed VLANs for Trunking Ports

You can specify the IDs for the VLANs that are allowed on the specific trunk port.


Note

The switchport trunk allowed vlan vlan-list command replaces the current VLAN list on the specified port with the new list. You are prompted for confirmation before the new list is applied.

If you are doing a copy and paste of a large configuration, you might see some failures because the CLI is waiting for a confirmation before accepting other commands. To avoid this problem, you can disable prompting by using the terminal dont-ask command before you paste the configuration.

Before you begin

Before you configure the allowed VLANs for the specified trunk ports, ensure that you are configuring the correct interfaces and that the interfaces are trunks.

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

interface {ethernet slot/port | port-channel number}

Example:

switch(config)# interface ethernet 1/1

Specifies an interface to configure, and enters interface configuration mode.

Step 3

switchport trunk allowed vlan {vlan-list add vlan-list | all | except vlan-list | none | remove vlan-list}

Example:

switch(config-if)# switchport trunk allowed vlan add 15-20#

Sets the allowed VLANs for the trunk interface. The default is to allow all VLANs on the trunk interface: 1 to 3967 and 4048 to 4094.

Step 4

exit

Example:

switch(config-if)# exit
switch(config)#

Exits the interface mode.

Step 5

show vlan

Example:

switch# show vlan

(Optional) Displays the status and information for VLANs.

Step 6

no shutdown

Example:

switch# configure terminal
switch(config)# int e1/1
switch(config-if)# no shutdown

(Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

Step 7

copy running-config startup-config

Example:

switch(config)# copy running-config startup-config

(Optional) Copies the running configuration to the startup configuration.

Example

This example shows how to add VLANs 15 to 20 to the list of allowed VLANs on the Ethernet 1/1, Layer 2 trunk port: 

switch# configure terminal 
switch(config)# interface ethernet 1/1
switch(config-if)# switchport trunk allowed vlan 15-20
switch(config-if)#

Configuring a Default Interface

The default interface feature allows you to clear the existing configuration of multiple interfaces such as Ethernet, loopback, VLAN network, port-channel, and tunnel interfaces. All user configuration under a specified interface will be deleted. You can optionally create a checkpoint before clearing the interface configuration so that you can later restore the deleted configuration.


Note

The default interface feature is not supported for management interfaces because the device could go to an unreachable state.

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

default interface int-if [checkpoint name]

Example:

switch(config)# default interface ethernet 1/1 checkpoint test8

Deletes the configuration of the interface and restores the default configuration. Use the ? keyword to display the supported interfaces.

Use the checkpoint keyword to store a copy of the running configuration of the interface before clearing the configuration.

Step 3

exit

Example:

switch(config)# exit
switch(config)#

Exits global configuration mode.

Step 4

show interface

Example:

switch# show interface

(Optional) Displays the interface status and information.

Step 5

no shutdown

Example:

switch# configure terminal
switch(config)# int e1/1
switch(config-if)# no shutdown

(Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

Example

This example shows how to delete the configuration of an Ethernet interface while saving a checkpoint of the running configuration for rollback purposes: 

switch# configure terminal 
switch(config)# default interface ethernet 1/1 checkpoint test8
.......Done 
switch(config)#

Changing the System Default Port Mode to Layer 2

You can set the system default port mode to Layer 2 access ports.

Procedure

  Command or Action Purpose

Step 1

configure terminal

Example:

switch# configure terminal
switch(config)#

Enters global configuration mode.

Step 2

system default switchport [shutdown]

Example:

switch(config-if)# system default switchport

Sets the default port mode for all interfaces on the system to Layer 2 access port mode and enters interface configuration mode. By default, all the interfaces are Layer 3.

Note

 

When the system default switchport shutdown command is issued:

  • Any Layer 2 port that is not specifically configured with no shutdown are shutdown. To avoid the shutdown, configure the Layer 2 port with no shut

Step 3

exit

Example:

switch(config-if)# exit
switch(config)#

Exits the interface configuration mode.

Step 4

show interface brief

Example:

switch# show interface brief

(Optional) Displays the status and information for interfaces.

Step 5

no shutdown

Example:

switch# configure terminal
switch(config)# int e1/1
switch(config-if)# no shutdown

(Optional) Clears the errors on the interfaces and VLANs where policies correspond with hardware policies. This command allows policy programming to continue and the port to come up. If policies do not correspond, the errors are placed in an error-disabled policy state.

Step 6

copy running-config startup-config

Example:

switch(config)# copy running-config startup-config

(Optional) Copies the running configuration to the startup configuration.

Example

This example shows how to set the system ports to be Layer 2 access ports by default: 

switch# configure terminal 
switch(config-if)# system default switchport
switch(config-if)#

Verifying the Interface Configuration

To display access and trunk interface configuration information, perform one of the following tasks.

Command

Purpose

show interface ethernet slot/port [brief | | counters | debounce | description | flowcontrol | mac-address | status | transceiver]

Displays the interface configuration.

show interface brief

Displays interface configuration information, including the mode.

show interface switchport

Displays information, including access and trunk interface, information for all Layer 2 interfaces.

show interface trunk [module module-number | vlan vlan-id]

Displays trunk configuration information.

show interface capabilities

Displays information about the capabilities of the interfaces.

show running-config [all]

Displays information about the current configuration.

The all command displays the default and current configurations.

show running-config interface ethernet slot/port

Displays configuration information about the specified interface.

show running-config interface port-channel slot/port

Displays configuration information about the specified port-channel interface.

show running-config interface vlan vlan-id

Displays configuration information about the specified VLAN interface.

Monitoring the Layer 2 Interfaces

Use the following commands to display Layer 2 interfaces:

Command

Purpose

clear counters interface [interface]

Clears the counters.

show interface counters [module module]

Displays input and output octets unicast packets, multicast packets, and broadcast packets.

show interface counters detailed [all]

Displays input packets, bytes, and multicast as well as output packets and bytes.

show interface counters errors [module module]

Displays information on the number of error packets.

Configuration Examples for Access and Trunk Ports

This example shows how to configure a Layer 2 access interface and assign the access VLAN mode for that interface:

switch# configure terminal
switch(config)# interface ethernet 1/30
switch(config-if)# switchport
switch(config-if)# switchport mode access
switch(config-if)# switchport access vlan 5
switch(config-if)#

This example shows how to configure a Layer 2 trunk interface, assign the native VLAN and the allowed VLANs, and configure the device to tag the native VLAN traffic on the trunk interface: 

switch# configure terminal
switch(config)# interface ethernet 1/35
switch(config-if)# switchport
switch(config-if)# switchport mode trunk
switch(config-if)# switchport trunk native vlan 10
switch(config-if)# switchport trunk allowed vlan 5, 10
switch(config-if)# exit
switch(config)#

Related Documents

Related Documents

Document Title

Configuring Layer 3 interfaces

Configuring Layer 2 Interfaces section

Port Channels

Configuring Port Channels section

VLANs, and STP

Cisco Nexus® 3550-T Layer 2 Switching Configuration chapter

System management

Cisco Nexus® 3550-T System Management Configuration chapter

High availability

Cisco Nexus® Series High Availability and Redundancy Guide

Licensing

Cisco NX-OS Licensing Guide

Release Notes

Cisco Nexus® Series NX-OS Release Notes