Table Of Contents
Configuring Layer 2 Interfaces
Information About Access and Trunk Interfaces
Access and Trunk Interfaces
IEEE 802.1Q Encapsulation
High Availability
Guidelines and Limitations
Default Settings
Configuring Access and Trunk Interfaces
Configuring a LAN Interface as a Layer 2 Access Port
Configuring Access Host Ports
Configuring Trunk Ports
Configuring the Native VLAN for 802.1Q Trunking Ports
Configuring the Allowed VLANs for Trunking Ports
Configuring the Device to Tag Native VLAN Traffic
Verifying the Interface Configuration
Monitoring the Interface Configuration
Configuration Examples for Access and Trunk Port Mode
Additional References
Related Documents
Standards
Feature History for Layer 2 Interface Parameters
Configuring Layer 2 Interfaces
This chapter describes how to configure Layer 2 switching ports as access or trunk ports.
This chapter includes the following sections:
•
Information About Access and Trunk Interfaces
•Guidelines and Limitations
•Configuring Access and Trunk Interfaces
•Verifying the Interface Configuration
•Monitoring the Interface Configuration
•Configuration Examples for Access and Trunk Port Mode
•Default Settings
•Additional References
•Feature History for Layer 2 Interface Parameters
Note For information about configuring a Switched Port Analyzer (SPAN) destination interface, see the Cisco Nexus 1000V System Management Configuration Guide, Release 4.0(4)SV1(2).
Note for information about VLANs, MAC address tables, and private VLANs, see the Cisco Nexus 1000V Layer 2 Switching Configuration Guide, Release 4.0(4)SV1(2).
Information About Access and Trunk Interfaces
This section includes the following topics:
•Access and Trunk Interfaces
•IEEE 802.1Q Encapsulation
•High Availability
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 ports on the Cisco Nexus 1000V are Layer 2 ports. You can change the default port mode (access or trunk). See the Cisco Nexus 1000V Getting Started Guide, Release 4.0(4)SV1(2) for information about setting the default port mode.
Figure 3-1 shows how you can use trunk ports in the network. The trunk port carries traffic for two or more VLANs.
Figure 3-1 Trunk and Access Ports and VLAN Traffic
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.
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.
IEEE 802.1Q Encapsulation
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 (see Figure 3-2 and Figure 3-3). 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 3-2 Header Without 802.1Q Tag
Figure 3-3 Header With 802.1Q Tag
High Availability
High availability is supported for Layer 2 ports.
Guidelines and Limitations
VLAN trunking has the following guidelines and limitations:
•Do not connect devices with access links because access links may partition a VLAN.
•When connecting Cisco switches 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.
•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.
•If you try to enable 802.1X on a trunk port, an error message appears, and 802.1X is not enabled.
•If you try to change the mode of an 802.1X-enabled port to trunk, the port mode is not changed.
Default Settings
The following table lists the default settings for Layer 2 interfaces.
Parameters
|
Default
|
Switchport mode
|
Access
|
Allowed VLANs
|
1 to 3967, 4048 to 4094
|
Access VLAN ID
|
VLAN1
|
Native VLAN ID
|
VLAN1
|
Native VLAN ID tagging
|
Disabled
|
Administrative state
|
Shut
|
Configuring Access and Trunk Interfaces
This section includes the following topics:
•Configuring a LAN Interface as a Layer 2 Access Port
•Configuring Access Host Ports
•Configuring Trunk Ports
•Configuring the Native VLAN for 802.1Q Trunking Ports
•Configuring the Allowed VLANs for Trunking Ports
•Configuring the Device to Tag Native VLAN Traffic
Note Be aware that the Cisco Nexus 1000V commands may differ from the Cisco IOS commands.
Configuring a LAN Interface as a Layer 2 Access Port
Use this procedure to configure a Layer 2 port as an access port.
BEFORE YOU BEGIN
Before beginning this procedure, you must know or do the following:
•You are logged in to the CLI in EXEC mode.
•The interface can be either Ethernet or vEthernet.
•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.
SUMMARY STEPS
1. config t
2. interface interface
3. switchport mode access
4. switchport access vlan vlan-id
5. exit
6. show interface
7. copy running-config startup-config
DETAILED STEPS
| |
Command
|
Purpose
|
Step 1
|
config t
Example:
n1000v# config t
n1000v(config)#
|
Places you into global configuration mode.
|
Step 2
|
interface interface
Example 1:
n1000v(config)# interface ethernet 3/1
n1000v(config-if)#
|
Specifies the interface that you are configuring and places you in interface configuration mode.
•For an Ethernet port, use ethernet slot/port, where slot is the module slot number and port is the port number.
•For a vEthernet port, use vethernet interface-number, where interface-number is a number from 1 to 1048575.
|
Step 3
|
switchport mode access
Example:
n1000v(config-if)# switchport mode
access
|
Sets the interface as a nontrunking nontagged, single-VLAN Layer 2 interface in the running configuration.
|
Step 4
|
switchport access vlan vlan-id
Example:
n1000v(config-if)# switchport access
vlan 5
|
(Optional) Specifies the VLAN for which this access port will carry traffic and saves the change in the running configuration. 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:
n1000v(config-if)# exit
n1000v(config)#
|
Exits the interface configuration mode and returns you to global configuration mode.
|
Step 6
|
show interface
Example:
n1000v(config)# show interface
|
(Optional) Displays the interface status and information.
|
Step 7
|
copy running-config startup-config
Example:
n1000v(config)# copy running-config
startup-config
|
(Optional) Saves the running configuration persistently through reboots and restarts by copying it to the startup configuration.
|
EXAMPLES
The following example shows how to set Ethernet 3/1 as a Layer 2 access port that carries traffic for VLAN 5 only:
n1000v(config)# interface ethernet 3/1
n1000v(config-if)# switchport mode access
n1000v(config-if)# switchport access vlan 5
Configuring Access Host Ports
Use this procedure to configure a port as an access port in order to optimize the performance of ports connected to end stations.
BEFORE YOU BEGIN
Before beginning this procedure, you must know or do the following:
•You are logged in to the CLI in EXEC mode.
•Ensure that you are configuring the correct interface to an interface that is an end station.
•You should apply the switchport host command only to interfaces that are connected to an end station.
•An access host port handles the Spanning Tree Protocol (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 Chapter 5 "Configuring Port Channels" for information about port channel interfaces.
•The interface can be either Ethernet or vEthernet.
SUMMARY STEPS
1. config t
2. interface interface
3. switchport host
4. exit
5. show interface
6. copy running-config startup-config
DETAILED STEPS
| |
Command
|
Purpose
|
Step 1
|
config t
Example:
n1000v# config t
n1000v(config)#
|
Places you into global configuration mode.
|
Step 2
|
interface interface
Example:
n1000v(config)# interface ethernet 3/1
n1000v(config-if)#
|
Specifies the interface that you are configuring and places you in interface configuration mode.
•For an Ethernet port, use ethernet slot/port, where slot is the module slot number and port is the port number.
•For a vEthernet port, use vethernet interface-number, where interface-number is a number from 1 to 1048575.
|
Step 3
|
switchport host
Example:
n1000v(config-if)# switchport host
|
Designates the interface as an access host port in the running configuration, which immediately moves it 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:
n1000v(config-if)# exit
n1000v(config)#
|
Exits the interface configuration mode and returns you to global configuration mode.
|
Step 5
|
show interface
Example:
n1000v(config)# show interface
|
(Optional) Displays the interface status and information.
|
Step 6
|
copy running-config startup-config
Example:
n1000v(config)# copy running-config
startup-config
|
(Optional) Saves the running configuration persistently through reboots and restarts by copying it to the startup configuration.
|
EXAMPLES
The following example shows how to set Ethernet 3/1 as a Layer 2 access port with PortFast enabled and port channel disabled:
n1000v(config)# interface ethernet 3/1
n1000v(config-if)# switchport host
Configuring Trunk Ports
Use this procedure to configure a Layer 2 port as a trunk port.
BEFORE YOU BEGIN
Before beginning this procedure, you must know or do the following:
•You are logged in to the CLI in EXEC mode.
•Before you configure a trunk port, ensure that you are configuring a Layer 2 interface.
•The interface can be either Ethernet or vEthernet.
•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.)
•The device supports 802.1Q encapsulation only.
SUMMARY STEPS
1. config t
2. interface interface
3. switchport mode trunk
4. exit
5. show interface
6. copy running-config startup-config
DETAILED STEPS
| |
Command
|
Purpose
|
Step 1
|
config t
Example:
n1000v# config t
n1000v(config)#
|
Places you into global configuration mode.
|
Step 2
|
interface interface
Example:
n1000v(config)# interface ethernet 3/1
n1000v(config-if)#
|
Specifies the interface that you are configuring and places you in interface configuration mode.
•For an Ethernet port, use ethernet slot/port, where slot is the module slot number and port is the port number.
•For a vEthernet port, use vethernet interface-number, where interface-number is a number from 1 to 1048575.
|
Step 3
|
switchport mode trunk
Example:
n1000v(config-if)# switchport mode trunk
|
Sets the interface as a Layer 2 trunk port in the running configuration. 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:
n1000v(config-if)# exit
n1000v(config)#
|
Exits the interface configuration mode and returns you to global configuration mode.
|
Step 5
|
show interface
Example:
n1000v(config)# show interface
|
(Optional) Displays the interface status and information.
|
Step 6
|
copy running-config startup-config
Example:
n1000v(config)# copy running-config
startup-config
|
(Optional Saves the running configuration persistently through reboots and restarts by copying it to the startup configuration.
|
EXAMPLES
The following example shows how to set Ethernet 3/1 as a Layer 2 trunk port:
n1000v(config)# interface ethernet 3/1
n1000v(config-if)# switchport mode trunk
Configuring the Native VLAN for 802.1Q Trunking Ports
Use this procedure to configure the native VLAN for 802.1Q trunk ports.
BEFORE YOU BEGIN
Before beginning this procedure, you must know or do the following:
•You are logged in to the CLI in EXEC mode.
•If you do not configure a native VLAN, the trunk port uses the default VLAN as the native VLAN ID.
SUMMARY STEPS
1. config t
2. interface interface
3. switchport trunk native vlan vlan-id
4. exit
5. show vlan
6. copy running-config startup-config
DETAILED STEPS
| |
Command
|
Purpose
|
Step 1
|
config t
Example:
n1000v# config t
n1000v(config)#
|
Places you into global configuration mode.
|
Step 2
|
interface interface
Example:
n1000v(config)# interface ethernet 3/1
n1000v(config-if)#
|
Specifies the interface that you are configuring and places you in interface configuration mode.
•For an Ethernet port, use ethernet slot/port, where slot is the module slot number and port is the port number.
•For a vEthernet port, use vethernet interface-number, where interface-number is a number from 1 to 1048575.
|
Step 3
|
switchport trunk native vlan vlan-id
Example:
n1000v(config-if)# switchport trunk
native vlan 5
|
Designates the native VLAN for the 802.1Q trunk in the running configuration. Valid values are from 1 to 4094, except those VLANs reserved for internal use. The default value is VLAN1.
|
Step 4
|
exit
Example:
n1000v(config-if)# exit
n1000v(config)#
|
Exits the interface configuration mode and returns you to global configuration mode.
|
Step 5
|
show vlan
Example:
n1000v(config)# show vlan
|
(Optional) Displays the status and information of VLANs.
|
Step 6
|
copy running-config startup-config
Example:
n1000v(config)# copy running-config
startup-config
|
(Optional) Saves the running configuration persistently through reboots and restarts by copying it to the startup configuration.
|
EXAMPLES
The following example shows how to set the native VLAN for the Ethernet 3/1, Layer 2 trunk port to VLAN 5:
n1000v(config)# interface ethernet 3/1
n1000v(config-if)# switchport trunk native vlan 5
Configuring the Allowed VLANs for Trunking Ports
Use this procedure to specify the VLAN IDs that are allowed on a trunk port.
BEFORE YOU BEGIN
Before beginning this procedure, you must know or do the following:
•You are logged in to the CLI in EXEC mode.
•Make sure that you are configuring the correct interface and that the interface is a trunk.
SUMMARY STEPS
1. config t
2. interface interface
3. switchport trunk allowed vlan {vlan-list | all | none | [add | except | | remove {vlan-list}]}
4. exit
5. show vlan
6. copy running-config startup-config
DETAILED STEPS
| |
Command
|
Purpose
|
Step 1
|
config t
Example:
n1000v# config t
n1000v(config)#
|
Places you into global configuration mode.
|
Step 2
|
interface interface
Example:
n1000v(config)# interface ethernet 3/1
n1000v(config-if)#
|
Specifies the interface that you are configuring and places you in interface configuration mode.
•For an Ethernet port, use ethernet slot/port, where slot is the module slot number and port is the port number.
•For a vEthernet port, use vethernet interface-number, where interface-number is a number from 1 to 1048575.
|
Step 3
|
switchport trunk allowed vlan {vlan-list
all | none [add |except | none | remove
{vlan-list}]}
Example:
n1000v(config-if)# switchport trunk
allowed vlan add 15-20#
|
Sets the allowed VLANs for the trunk interface in the running configuration. The default is to allow all VLANs on the trunk interface. The range is from 1 to 3967 and 4048 to 4094. VLANs 3968 to 4047 are the default VLANs reserved for internal use by default; this group of VLANs is configurable. By default, all VLANs are allowed on all trunk interfaces.
Note You cannot add internally allocated VLANs as allowed VLANs on trunk ports. The system returns a message if you attempt to list an internally allocated VLAn as an allowed VLAN.
|
Step 4
|
exit
Example:
n1000v(config-if)# exit
n1000v(config)#
|
Exits the interface configuration mode and returns you to global configuration mode.
|
Step 5
|
show vlan
Example:
n1000v# show vlan
|
(Optional) Displays the status and information for VLANs.
|
Step 6
|
copy running-config startup-config
Example:
n1000v(config)# copy running-config
startup-config
|
(Optional) Saves the running configuration persistently through reboots and restarts by copying it to the startup configuration.
|
EXAMPLES
The following example shows how to add VLANs 15 to 20 to the list of allowed VLANs on the Ethernet 3/1, Layer 2 trunk port:
n1000v(config)# interface ethernet 3/1
n1000v(config-if)# switchport trunk allowed vlan 15-20
Configuring the Device to Tag Native VLAN Traffic
Use this procedure to maintain tagging on a packet that enters an 802.1Q trunked interface with a tag matching the native VLAN ID. Untagged traffic is dropped although control traffic is still carried on the interface.
BEFORE YOU BEGIN
Before beginning this procedure, you must know or do the following:
•You are logged in to the CLI in EXEC mode.
•The vlan dot1q tag native global command changes the behavior of all native VLAN ID interfaces on all trunks on the device.
•This feature applies to the entire device; you cannot apply it to selected VLANs on a device.
Note If you enable 802.1Q tagging on one device and disable it on another device, all traffic is dropped on the device with this feature disabled. You must configure this feature identically on each device.
SUMMARY STEPS
1. config t
2. vlan dot1q tag native
3. exit
4. show vlan
5. copy running-config startup-config
DETAILED STEPS
| |
Command
|
Purpose
|
Step 1
|
config t
Example:
n1000v# config t
n1000v(config)#
|
Places you into global configuration mode.
|
Step 2
|
vlan dot1q tag native
Example:
n1000v(config)# vlan dot1q tag native
|
Modifies the behavior of a 802.1Q trunked native VLAN ID interface in the running configuration. The interface maintains the taggings for all packets that enter with a tag that matches the value of the native VLAN ID and drops all untagged traffic. The control traffic is still carried on the native VLAN. The default is disabled.
|
Step 3
|
exit
Example:
n1000v(config)# exit
n1000v#
|
Exits global configuration mode and returns you to EXEC mode.
|
Step 4
|
show vlan
Example:
n1000v# show vlan
|
(Optional) Displays the status and information for VLANs.
|
Step 5
|
copy running-config startup-config
Example:
n1000v# copy running-config
startup-config
|
(Optional) Saves the running configuration persistently through reboots and restarts by copying it to the startup configuration.
|
EXAMPLES
The following example shows how to change the behavior of the native VLAN on an 802.1Q trunked interface to maintain the tagged packets and drop all untagged traffic (except control traffic):
n1000v(config)# vlan dot1q tag native
Verifying the Interface Configuration
Use the following commands to display and verify access and trunk interface information.
Command
|
Purpose
|
show interface ethernet slot/port [brief | | counters | debounce | description | mac-address | status | transceiver]
|
Displays the interface configuration
|
show interface ethernet slot/port counters [brief | detailed | errors | snmp | storm-control | trunk]
|
Displays the counters for a specified Ethernet interface.
|
show interface ethernet slot/port status [err-disable]
|
Displays the status for a specified Ethernet interface.
|
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 on the capabilities of the interfaces.
|
show running-config interface ethernet slot/port
|
Displays configuration information about the specified interface.
|
Monitoring the Interface Configuration
Use the following commands to display and monitor access and trunk interface information.
Command
|
Purpose
|
clear counters [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 Port Mode
The following example shows how to configure a Layer 2 access interface and assign the access VLAN for that interface:
n1000v# configure terminal
n1000v(config)# interface ethernet 2/30
n1000v(config-if)# switchport
n1000v(config-if)# switchport mode access
n1000v(config-if)# switchport access vlan 5
The following 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:
n1000v# configure terminal
n1000v(config)# interface ethernet 2/35
n1000v(config-if)# switchport
n1000v(config-if)# switchport mode trunk
n1000v(config-if)# switchport trunk native vlan 10
n1000v(config-if)# switchport trunk allowed vlan 5, 10
n1000v(config)# vlan dot1q tag native
Additional References
For additional information related to implementing access and trunk port modes, see the following sections:
•Related Documents
•Standards
Related Documents
Related Topic
|
Document Title
|
Port channels
|
Chapter 5 "Configuring Port Channels"
|
VLANs, private VLANs, and STP
|
Cisco Nexus 1000V Layer 2 Switching Configuration Guide, Release 4.0(4)SV1(2)
|
System management
|
Cisco Nexus 1000V System Management Configuration Guide, Release 4.0(4)SV1(2)
|
Release Notes
|
Cisco Nexus 1000V Release Notes, Release 4.0(4)SV1(2)
|
Standards
Standards
|
Title
|
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
|
—
|
Feature History for Layer 2 Interface Parameters
This section provides the feature history for Layer 2 interface parameters.
Feature Name
|
Releases
|
Feature Information
|
Layer 2 interface parameters
|
4.0
|
This feature was introduced.
|
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