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This chapter contains the following sections:
Information About the Basic Interface Parameters
For the vEthernet, Ethernet, and management interfaces, you can configure the description parameter to provide a name for the interface. Using a unique name for each interface allows you to quickly identify the interface when you are looking at a listing of multiple interfaces.
By default, the description for vEthernet interfaces is automatically formatted to contain information about the connected device. The description for a virtual Network Interface Card (vNIC), for example, contains the VM name and network adapter number. You keep this default description or you can override it with a description of your choosing.
The speed and duplex modes are interrelated for each Ethernet and management interface. By default, each interface autonegotiates its speed and duplex modes with the other interface, but you can change these settings. If you change the settings, be sure to use the same speed and duplex mode settings on both interfaces or use autonegotiation for at least one of the interfaces.
The maximum transmission unit (MTU) size specifies the maximum frame size that an Ethernet port can process. For transmissions to occur between two ports, you must configure the same MTU size for both ports. A port drops any frames that exceed its MTU size.
By default, the MTU size for each port is 1500 bytes, which is the IEEE 802.3 standard for Ethernet frames. Larger MTU sizes are possible for more efficient processing of data with less overhead. The larger frames, called jumbo frames, can be up to 9000 bytes in size, which is also the fixed system jumbo MTU size in the Cisco Nexus 1000V.
For a Layer 2 port, you can configure an MTU size as the system default of 1500 bytes or the system default jumbo MTU size of 9000 bytes.
The administrative-status parameter determines whether an interface is up or down. When an interface is administratively down, it is disabled and unable to transmit data. When an interface is administratively up, it is enabled and able to transmit data.
The Cisco Discovery Protocol (CDP) is a Layer 2 protocol that enables two devices that run CDP to learn about each other. You can use CDP to troubleshoot the network by displaying information about the neighboring devices that are linked through each interface. By default, CDP is enabled.
A port channel is an aggregation of multiple physical interfaces that comprise a logical interface. You can bundle up to eight individual interfaces into a port channel to provide increased bandwidth and redundancy. Port channeling also load balances traffic across these physical interfaces. The port channel stays operational if at least one physical interface within the port channel is operational.
Any configuration changes that you apply to the port channel are applied to each interface member of that port channel.
Interface parameters have the following configuration guidelines and limitations:
You usually configure Ethernet port speed and duplex mode parameters to auto to allow negotiation of the speed and duplex modes between ports. If you decide to configure the port speed and duplex modes manually for these ports, consider the following:
If you set the Ethernet port speed to auto, the device automatically sets the duplex mode to auto.
If you enter the no speed command, the device automatically sets both the speed and duplex parameters to auto (the no speed command produces the same results as the speed auto command).
If you configure an Ethernet port speed to a value other than auto (for example, 10, 100, or 1000 Mbps), you must configure the connecting port to match. Do not configure the connecting port to negotiate the speed.
![]() Note | The device cannot automatically negotiate the Ethernet port speed and duplex modes if the connecting port is configured to a value other than auto. |
![]() Note | Changing the Ethernet port speed and duplex mode configuration might shut down and reenable the interface. |
To specify an interface in the CLI, use the following guidelines:
For an Ethernet port, use the ethernet slot/port command, where slot is the module slot number and port is the port number.
For a vEthernet port, use the vethernet number command, where number is a number from 1 to 1048575.
A space is not required between the interface type and the slot/port or interface number. For example, for the Ethernet slot 4, port 5 interface, you can specify either the ethernet 4/5 command or the ethernet4/5 command.
Jumbo frames are only supported on the vmxnet3 driver. Attempts to change the MTU appear to succeed but the adapter always drops frames larger than 1500 bytes. For more information, see the VMware KB article http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1015556.
Configuring the Basic Interface Parameters
You can specify an interface to configure.
Log in to the CLI in EXEC mode.
This example shows how to specify an interface to configure:
switch# configure terminal switch(config)# interface ethernet 3/1 switch(config-if)# show interface ethernet 3/1 switch(config-if)#
You can add a description to an Ethernet, vEthernet, or management interface.
This example shows how to set the interface description to Ethernet port 24 on module 3:
switch# configure terminal switch(config)# interface ethernet 3/24 switch(config-if)# description Ethernet port 24 on module 3 switch(config-if)#
You can configure the interface speed and duplex modes.
Log in to the CLI in EXEC mode.
![]() Note | The interface speed that you specify can affect the duplex mode used for an interface, so you should set the speed before setting the duplex mode. If you set the speed for autonegotiation, the duplex mode is automatically set to be autonegotiated. If you specify a speed of 10 Mbps or 100 Mbps, the port is automatically configured to use half-duplex mode, but you can specify full-duplex mode instead. If you specify a speed of 1000 Mbps (1 Gbps) or faster, full duplex is automatically used. |
Make sure that the remote port has a speed setting that supports your changes for the local port. If you want to set the local port to use a specific speed, you must set the remote port for the same speed or set the local port to automatically negotiate the speed.
This example shows how to set the port speed and duplex mode to Ethernet port 1 on module 3:
switch# configure terminal switch(config)# interface ethernet 3/1 switch(config-if)# speed 1000 switch(config-if)# duplex full switch(config-if)# show interface ethernet 3/1 switch(config-if)#
You can configure the size of the maximum transmission unit (MTU) for a Layer 2 Ethernet interface.
Log in to the CLI in EXEC mode.
Specify an MTU size between 1500 and 9000 bytes for an Ethernet interface.
Make sure that the MTU value you set is supported by the VEM physical NIC. See your VMware documentation for more information about supported MTU for physical NICs.
Know that Jumbo frames are supported only on the vmxnet3 driver. Attempts to change the MTU appear to succeed but the adapter always drops frames larger than 1500 bytes. For more information, see the VMware KB article http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1015556
This example shows how to configure the Ethernet interface 3/1 with the default MTU size of 1500 bytes:
switch# configure terminal switch# interface ethernet 3/1 switch(config-if)# mtu 1500 switch(config-if)#
You can shut down and restart Ethernet or management interfaces.
This example shows how to disable the interface Ethernet port 1 on module 3:
switch# configure terminal switch(config)# interface ethernet 3/1 switch(config-if)# shutdown switch(config-if)# no shutdown switch(config-if)#
You can enable or disable the Cisco Discovery Protocol (CDP) for Ethernet and management interfaces.
This example shows how to enable CDP for Ethernet port 3/1:
switch# configure terminal switch(config)# interface ethernet 3/1 switch(config-if)# cdp enable switch(config-if)#
This example shows how to disable CDP for Ethernet port 3/1:
switch# configure terminal switch(config)# interface ethernet 3/1 switch(config-if)# no cdp enable switch(config-if)#
You can clear the Ethernet, vEthernet, and management interface counters.
Log in to the CLI in EXEC mode, configuration mode, or interface configuration mode.
Command or Action | Purpose |
---|
This example shows how to clear and reset the counters on Ethernet port 5/5:
switch# clear counters ethernet 5/5 switch#
Use one of the following commands to verify the configuration:
Command | Purpose |
---|---|
show cdp |
Displays the CDP status. |
show interface interface |
Displays the configured states of one or all interfaces. |
show interface brief |
Displays a table of interface states. |
show interface switchport |
Displays the status of Layer 2 ports. |
Feature Name |
Releases |
Feature Information |
---|---|---|
System jumbo MTU |
4.2(1)SV1(4) |
The system jumbo MTU is fixed at 9000 and cannot be changed. |
Interface MTU |
4.2(1)SV1(4) |
The interface MTU can be configured as a value between 1500 and 9000. |
Basic interface parameters |
4.0(4)SV1(1) |
This feature was introduced. |