Configuring Layer 2 Interfaces

This chapter contains the following sections:

Information About Ethernet Interfaces

The Ethernet ports can operate as standard Ethernet interfaces connected to servers or to a LAN.

The Ethernet interfaces are enabled by default.

Interface Command

You can enable the various capabilities of the Ethernet interfaces on a per-interface basis using the interface command. When you enter the interface command, you specify the following information:

The interface numbering convention is extended to support use with a Cisco Nexus Fabric Extender as follows:

switch(config)# interface ethernet [chassis/]slot/port

  • The chassis ID is an optional entry that you can use to address the ports of a connected Fabric Extender. The chassis ID is configured on a physical Ethernet or EtherChannel interface on the switch to identify the Fabric Extender discovered through the interface. The chassis ID ranges from 100 to 199.

Unidirectional Link Detection Parameter

The Cisco-proprietary Unidirectional Link Detection (UDLD) protocol allows ports that are connected through fiber optics or copper (for example, Category 5 cabling) Ethernet cables to monitor the physical configuration of the cables and detect when a unidirectional link exists. When the switch detects a unidirectional link, UDLD shuts down the affected LAN port and alerts the user. Unidirectional links can cause a variety of problems, including spanning tree topology loops.

UDLD is a Layer 2 protocol that works with the Layer 1 protocols to determine the physical status of a link. At Layer 1, autonegotiation takes care of physical signaling and fault detection. UDLD performs tasks that autonegotiation cannot perform, such as detecting the identities of neighbors and shutting down misconnected LAN ports. When you enable both autonegotiation and UDLD, Layer 1 and Layer 2 detections work together to prevent physical and logical unidirectional connections and the malfunctioning of other protocols.

A unidirectional link occurs whenever traffic transmitted by the local device over a link is received by the neighbor but traffic transmitted from the neighbor is not received by the local device. If one of the fiber strands in a pair is disconnected, and if autonegotiation is active, the link does not stay up. In this case, the logical link is undetermined, and UDLD does not take any action. If both fibers are working normally at Layer 1, then UDLD at Layer 2 determines whether those fibers are connected correctly and whether traffic is flowing bidirectionally between the correct neighbors. This check cannot be performed by autonegotiation, because autonegotiation operates at Layer 1.

A Cisco Nexus device periodically transmits UDLD frames to neighbor devices on LAN ports with UDLD enabled. If the frames are echoed back within a specific time frame and they lack a specific acknowledgment (echo), the link is flagged as unidirectional and the LAN port is shut down. Devices on both ends of the link must support UDLD in order for the protocol to successfully identify and disable unidirectional links.

The following figure shows an example of a unidirectional link condition. Device B successfully receives traffic from Device A on the port. However, Device A does not receive traffic from Device B on the same port. UDLD detects the problem and disables the port.

Figure 1. Unidirectional Link

Default UDLD Configuration

The following table shows the default UDLD configuration.

Table 1  UDLD Default Configuration

Feature

Default Value

UDLD global enable state

Globally disabled

UDLD aggressive mode

Disabled

UDLD per-port enable state for fiber-optic media

Enabled on all Ethernet fiber-optic LAN ports

UDLD per-port enable state for twisted-pair (copper) media

Enabled

UDLD Aggressive and Nonaggressive Modes

UDLD aggressive mode is disabled by default. You can configure UDLD aggressive mode only on point-to-point links between network devices that support UDLD aggressive mode. If UDLD aggressive mode is enabled, when a port on a bidirectional link that has a UDLD neighbor relationship established stops receiving UDLD frames, UDLD tries to reestablish the connection with the neighbor. After eight failed retries, the port is disabled.

To prevent spanning tree loops, nonaggressive UDLD with the default interval of 15 seconds is fast enough to shut down a unidirectional link before a blocking port transitions to the forwarding state (with default spanning tree parameters).

When you enable the UDLD aggressive mode, the following occurs:

  • One side of a link has a port stuck (both transmission and receive)

  • One side of a link remains up while the other side of the link is down

In these cases, the UDLD aggressive mode disables one of the ports on the link, which prevents traffic from being discarded.

Interface Speed

Cisco Nexus 3000 Series switches have a number of fixed 10-Gigabit ports; each is equipped with SFP+ interface adapters. Cisco Nexus 3100 Series switches have 32 Quad Same Factor Pluggable (QSFP) ports and 4 SFP+ interface adapters. The default speed for these 32 ports is 40 Gbps.

40-Gigabit Ethernet Interface Speed

You can operate QSFP ports as either 40-Gigabit Ethernet or 4 x10-Gigabit Ethernet modes on Cisco Nexus 3132 and Cisco Nexus 3172 switches. By default, there are 32 ports in the 40-Gigabit Ethernet mode. These 40-Gigabit Ethernet ports are numbered in a 2-tuple naming convention. For example, the second 40-Gigabit Ethernet port is numbered as 1/2. The process of changing the configuration from 40-Gigabit Ethernet to 10-Gigabit Ethernet is called breakout and the process of changing the configuration from 10-Gigabit Ethernet to Gigabit Ethernet is called breakin. When you break out a 40-Gigabit Ethernet port into 10-Gigabit Ethernet ports, the resulting ports are numbered using a 3-tuple naming convention. For example, the break-out ports of the second 40-Gigabit Ethernet port are numbered as 1/2/1, 1/2/2, 1/2/3, 1/2/4.

You can break out the 40-Gigabit Ethernet port into four 10-Gigabit Ethernet ports by using the speed 10000 command and using a splitter cable to connect to multiple peer switches. You can break in four 10-Gigabit Ethernet ports to a 40-Gigabit Ethernet port by using the speed 40000 command. The configuration change from 40-Gigabit Ethernet to 10-Gigabit Ethernet and from 10-Gigabit Ethernet to 40-Gigabit Ethernet takes effect immediately. You do not need to reload the switch. A QSFP transceiver security check is also performed.


Note
When you break out from 40-Gigabit Ethernet to 10-Gigabit Ethernet, or break in from 10-Gigabit Ethernet to 40-Gigabit Ethernet, all interface configurations are reset, and the affected ports are administratively unavailable. To make these ports available, use the no shut command.

Note

Starting with Release 6.0(2)U5(1), a new QSFP+ 40-Gb transceiver is now supported on the Cisco Nexus 3000 Series switches. The new QSFP+ (40-Gb) transceiver has a cable that splits into four 10Gb SFP-10G-LR transceivers. To use it, you need the port to be in 4x10G mode. If you are using the breakout cable, you need to run that 40G port in 4x10G mode.

The ability to break out a 40-Gigabit Ethernet port into four 10-Gigabit Ethernet ports and break in four 10-Gigabit Ethernet ports into a 40-Gigabit Ethernet port dynamically allows you to use any of the breakout-capable ports to work in the 40-Gigabit Ethernet or 10-Gigabit Ethernet modes without permanently defining them.

For Cisco Nexus 3132Q switches, when the Ethernet interface 1/1 is in the 40-Gigabit Ethernet mode, the first QSFP port is active. After breakout, when the Ethernet interface 1/1/1-4 is in the 10-Gigabit Ethernet mode, you can choose to use either QSFP ports or SFP+ ports. However, both the first QSFP port and the four SFP+ ports cannot be active at the same time.

Port Modes

Cisco Nexus 3100 Series switches have various port modes. In Cisco NX-OS Release 6.0(2)U(2)1, only the Cisco Nexus 3132Q switch has port modes that support breakout. Cisco NX-OS Release 6.0(2)U(2)3 introduces breakout port modes for the Cisco Nexus 3172PQ switch.


Note

Prior to Release 6.0(2)U5(1), the default mode on Cisco Nexus 3132Q and Cisco Nexus 3132CR Series switches used to be Fixed32x40G mode. Starting with Release 6.0(2)U5(1), the default port mode on Cisco Nexus 3132Q and Cisco Nexus 3132CR Series switches after write erase is 32x40G mode.

Nexus 3100 Series Switches Ports Port Modes
Cisco Nexus 3132Q 32 x QSFP ports and 4 SFP+ ports
The following port modes support breakout:
  • 32x40G—This is an oversubscribed port mode. All 32 ports are oversubscribed and the first 24 QSFP ports are break-out capable. You cannot enter the speed 10000 command on ports 25 through 32. Starting with Release 6.0(2)U5(1), the 32x40G breakout mode is the default port mode.
  • 26x40G—This is an oversubscribed port mode. Of the 26 ports, 12 ports are nonoversubscribed (cut-through). These ports are 2,4 to 8,14,and 16 to 20. The remaining 14 ports are oversubscribed. All available QSFP ports are break-out capable.
  • 24x40G—This is the only nonoversubscribed (cut-through) mode. All available QSFP ports are break-out capable.

The Fixed32x40G port mode does not support breakout.

Cisco Nexus 3172PQ 6 x QSFP ports and 48 SFP+ ports
The following is the default port mode and supports breakout:
  • 48x10G+breakout6x40G
The following are the fixed port modes that do not support breakout:
  • 48x10G+6x40G
  • 72x10G

SVI Autostate

The Switch Virtual Interface (SVI) represents a logical interface between the bridging function and the routing function of a VLAN in the device. By default, when a VLAN interface has multiple ports in the VLAN, the SVI goes to the down state when all the ports in the VLAN go down.

Autostate behavior is the operational state of an interface that is governed by the state of the various ports in its corresponding VLAN. An SVI interface on a VLAN comes up when there is at least one port in that vlan that is in STP forwarding state. Similarly, this interface goes down when the last STP forwarding port goes down or goes to another STP state.

By default, Autostate calculation is enabled. You can disable Autostate calculation for an SVI interface and change the default value.


Note

Nexus 3000 Series switches do not support bridging between two VLANs when an SVI for one VLAN exists on the same device as the bridging link. Traffic coming into the device and bound for the SVI is dropped as a IPv4 discard. This is because the BIA MAC address is shared across VLANs/SVIs with no option to modify the MAC of the SVI.

Cisco Discovery Protocol

The Cisco Discovery Protocol (CDP) is a device discovery protocol that runs over Layer 2 (the data link layer) on all Cisco-manufactured devices (routers, bridges, access servers, and switches) and allows network management applications to discover Cisco devices that are neighbors of already known devices. With CDP, network management applications can learn the device type and the Simple Network Management Protocol (SNMP) agent address of neighboring devices that are running lower-layer, transparent protocols. This feature enables applications to send SNMP queries to neighboring devices.

CDP runs on all media that support Subnetwork Access Protocol (SNAP). Because CDP runs over the data-link layer only, two systems that support different network-layer protocols can learn about each other.

Each CDP-configured device sends periodic messages to a multicast address, advertising at least one address at which it can receive SNMP messages. The advertisements also contain time-to-live, or holdtime information, which is the length of time a receiving device holds CDP information before discarding it. Each device also listens to the messages sent by other devices to learn about neighboring devices.

The switch supports both CDP Version 1 and Version 2.

Default CDP Configuration

The following table shows the default CDP configuration.

Table 2  Default CDP Configuration

Feature

Default Setting

CDP interface state

Enabled

CDP timer (packet update frequency)

60 seconds

CDP holdtime (before discarding)

180 seconds

CDP Version-2 advertisements

Enabled

Error-Disabled State

An interface is in the error-disabled (err-disabled) state when the inteface is enabled administratively (using the no shutdown command) but disabled at runtime by any process. For example, if UDLD detects a unidirectional link, the interface is shut down at runtime. However, because the interface is administratively enabled, the interface status displays as err-disabled. Once an interface goes into the err-disabled state, you must manually reenable it or you can configure an automatic timeout recovery value. The err-disabled detection is enabled by default for all causes. The automatic recovery is not configured by default.

When an interface is in the err-disabled state, use the errdisable detect cause command to find information about the error.

You can configure the automatic err-disabled recovery timeout for a particular err-disabled cause by changing the time variable.

The errdisable recovery cause command provides automatic recovery after 300 seconds. To change the recovery period, use the errdisable recovery interval command to specify the timeout period. You can specify 30 to 65535 seconds.

To disable recovery of an interface from the err-disabled state, use the no errdisable recovery cause command.

The various options for the errdisable recover cause command are as follows:

  • all—Enables a timer to recover from all causes.

  • bpduguard—Enables a timer to recover from the bridge protocol data unit (BPDU) Guard error-disabled state.

  • failed-port-state—Enables a timer to recover from a Spanning Tree Protocol (STP) set port state failure.

  • link-flap—Enables a timer to recover from linkstate flapping.

  • pause-rate-limit—Enables a timer to recover from the pause rate limit error-disabled state.

  • udld—Enables a timer to recover from the Unidirectional Link Detection (UDLD) error-disabled state.

  • loopback—Enables a timer to recover from the loopback error-disabled state.

If you do not enable the err-disabled recovery for the cause, the interface stays in the err-disabled state until you enter the shutdown and no shutdown commands. If the recovery is enabled for a cause, the interface is brought out of the err-disabled state and allowed to retry operation once all the causes have timed out. Use the show interface status err-disabled command to display the reason behind the error.

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, management, VLAN, and the port-channel interface.

Debounce Timer Parameters

The debounce timer delays notification of a link change, which can decrease traffic loss due to network reconfiguration. You can configure the debounce timer separately for each Ethernet port and specify the delay time in milliseconds. The delay time can range from 0 milliseconds to 5000 milliseconds. By default, this parameter is set for 100 milliseconds, which results in the debounce timer not running. When this parameter is set to 0 milliseconds, the debounce timer is disabled.


Caution
Enabling the debounce timer causes the link-down detections to be delayed, which results in a loss of traffic during the debounce period. This situation might affect the convergence and reconvergence of some Layer 2 and Layer 3 protocols.

MTU Configuration

The Cisco Nexus device switch does not fragment frames. As a result, the switch cannot have two ports in the same Layer 2 domain with different maximum transmission units (MTUs). A per-physical Ethernet interface MTU is not supported. Instead, the MTU is set according to the QoS classes. You modify the MTU by setting class and policy maps.


Note

When you show the interface settings, a default MTU of 1500 is displayed for physical Ethernet interfaces.

Downlink Delay

You can operationally enable uplink SFP+ ports before downlink RJ-45 ports after a reload on a Cisco Nexus 3048 switch. You must delay enabling the RJ-45 ports in the hardware until the SFP+ ports are enabled.

You can configure a timer that during reload enables the downlink RJ-45 ports in hardware only after the specified timeout. This process allows the uplink SFP+ ports to be operational first. The timer is enabled in the hardware for only those ports that are admin-enable.

Downlink delay is disabled by default and must be explicitly enabled. When enabled, if the delay timer is not specified, it is set for a default delay of 20 seconds.

Default Physical Ethernet Settings

The following table lists the default settings for all physical Ethernet interfaces:

Parameter

Default Setting

Duplex

Auto (full-duplex)

Encapsulation

ARPA

MTU1

1500 bytes

Port Mode

Access

Speed

Auto (10000)

1 MTU cannot be changed per-physical Ethernet interface. You modify MTU by selecting maps of QoS classes.

Configuring Ethernet Interfaces

Configuring the UDLD Mode

You can configure normal or aggressive unidirectional link detection (UDLD) modes for Ethernet interfaces on devices configured to run UDLD. Before you can enable a UDLD mode for an interface, you must make sure that UDLD is already enabled on the device that includes the interface. UDLD must also be enabled on the other linked interface and its device.

To use the normal UDLD mode, you must configure one of the ports for normal mode and configure the other port for the normal or aggressive mode. To use the aggressive UDLD mode, you must configure both ports for the aggressive mode.


Note

Before you begin, UDLD must be enabled for the other linked port and its device.

Procedure
     Command or ActionPurpose
    Step 1 switch# configure terminal
     

    Enters global configuration mode.

     
    Step 2 switch(config)# feature udld
     

    Enables UDLD for the device.

     
    Step 3 switch(config)# no feature udld
     

    Disables UDLD for the device.

     
    Step 4 switch(config)# show udld global
     

    Displays the UDLD status for the device.

     
    Step 5 switch(config)# interface type slot/port
     

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

     
    Step 6 switch(config-if)# udld {enable | disable | aggressive}
     

    Enables the normal UDLD mode, disables UDLD, or enables the aggressive UDLD mode.

     
    Step 7 switch(config-if)# show udld interface
     

    Displays the UDLD status for the interface.

     

    This example shows how to enable UDLD for the switch: 

     
switch# configure terminal
switch(config)# feature udld

    This example shows how to enable the normal UDLD mode for an Ethernet port: 

     
switch# configure terminal
switch(config)# interface ethernet 1/4
switch(config-if)# udld enable

    This example shows how to enable the aggressive UDLD mode for an Ethernet port: 

    switch# configure terminal
switch(config)# interface ethernet 1/4
switch(config-if)# udld aggressive

    This example shows how to disable UDLD for an Ethernet port: 

     
switch# configure terminal
switch(config)# interface ethernet 1/4
switch(config-if)# udld disable

    This example shows how to disable UDLD for the switch: 

    switch# configure terminal
switch(config)# no feature udld

    Triggering the Link State Consistency Checker

    You can manually trigger the link state consistency checker to compare the hardware and software link status of an interface and display the results. To manually trigger the link state consistency checker and display the results, use the following command in any mode:

    Procedure
       Command or ActionPurpose
      Step 1switch# show consistency-checker link-state module slot  

      Starts a link state consistency check on the specified module and displays its results.

       

      This example shows how to trigger a Link State consistency check and display its results: 

      switch# show consistency-checker link-state module 1
Link State Checks: Link state only
Consistency Check: FAILED
No inconsistencies found for:
   Ethernet1/1
   Ethernet1/2
   Ethernet1/3
   Ethernet1/4
   Ethernet1/5
   Ethernet1/6
   Ethernet1/7
   Ethernet1/8
   Ethernet1/9
   Ethernet1/10
   Ethernet1/12
   Ethernet1/13
   Ethernet1/14
   Ethernet1/15   
Inconsistencies found for following interfaces:
   Ethernet1/11

      Changing an Interface Port Mode

      You can configure a Quad small form-factor pluggable (QSFP+) port by using the hardware profile portmode command. To restore the defaults, use the no form of these commands. The Cisco Nexus 3172PQ switch has 48x10g+breakout6x40g as the default port mode.


      Note

      Using the CVR-QSFP-SFP10G adapter does not work with the twinax cables in 40G ports on the Cisco Nexus 3000 Series platforms. You have to first configure the port for breakout. You can then use the first port in the breakout.

      Procedure
         Command or ActionPurpose
        Step 1switch# configure terminal  

        Enters global configuration mode.

         
        Step 2switch(config)# copy running-config bootflash: my-config.cfg  

        Copies the running configuration to the bootflash. You can use this file to configure your device later.

         
        Step 3switch(config)# write erase
         

        Removes all the interface configurations.

         
        Step 4switch(config)# reload
         

        Reloads the Cisco NX-OS software.

         
        Step 5switch(config)# [no] hardware profile portmode portmode
         

        Changes the interface port mode.

         
        Step 6switch(config)# hardware profile portmode portmode 2-tuple
                  		(Optional)

        Displays the port names in 2-tuple mode instead of the default 3-tuple convention mode.

         
        Step 7switch(config)# copy running-config startup-config   (Optional)

        Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

         
        Step 8switch(config)# reload
         

        Reloads the Cisco NX-OS software.

        Manually apply all the interface configuration. You can refer to the configuration file that you saved earlier.

        Note   

        The interface numbering changes if the ports are changed from 40G mode to 4x10G mode or vice versa.

         

        This example shows how to change the port mode to 48x10g+breakout6x40g for QSFP+ ports: 

        switch# configure terminal
switch(config)# copy running-config bootflash:my-config.cfg
switch(config)# write erase
switch(config)# reload
WARNING: This command will reboot the system
Do you want to continue? (y/n) [n] y
switch(config)# hardware profile portmode 48x10g+breakout6x40g
Warning: This command will take effect only after saving the configuration and reload!
Port configurations could get lost when port mode is changed!
switch(config)# copy running-config startup-config
switch(config)# reload
WARNING: This command will reboot the system
Do you want to continue? (y/n) [n] y

        This example shows how to change the port mode to 48x10g+4x40g for QSFP+ ports: 

        switch# configure terminal
switch(config)# copy running-config bootflash:my-config.cfg
switch(config)# write erase
switch(config)# reload
WARNING: This command will reboot the system
Do you want to continue? (y/n) [n] y
switch(config)# hardware profile portmode 48x10g+4x40g
Warning: This command will take effect only after saving the configuration and reload!
Port configurations could get lost when port mode is changed!
switch(config)# copy running-config startup-config
switch(config)# reload
WARNING: This command will reboot the system
Do you want to continue? (y/n) [n] y

        This example shows how to change the port mode to 48x10g+4x40g for QSFP+ ports and verify the changes: 

        switch# configure terminal
switch(config)# hardware profile portmode 48x10g+4x40g
Warning: This command will take effect only after saving the configuration and r
eload! Port configurations could get lost when port mode is changed!
switch(config)# show running-config
!Command: show running-config
!Time: Thu Aug 25 07:39:37 2011
version 5.0(3)U2(1)
feature telnet
no feature ssh
feature lldp
username admin password 5 $1$OOV4MdOM$BAB5RkD22YanT4empqqSM0 role network-admin
ip domain-lookup
switchname BLR-QG-5
ip access-list my-acl
10 deny ip any 10.0.0.1/32
20 deny ip 10.1.1.1/32 any
class-map type control-plane match-any copp-arp
class-map type control-plane match-any copp-bpdu
:
:
control-plane
service-policy input copp-system-policy
hardware profile tcam region arpacl 128
hardware profile tcam region ifacl 256
hardware profile tcam region racl 256
hardware profile tcam region vacl 512
hardware profile portmode 48x10G+4x40G
snmp-server user admin network-admin auth md5 0xdd1d21ee42e93106836cdefd1a60e062
<--Output truncated-->
switch#

        This example shows how to restore the default port mode for QSFP+ ports: 

        switch# configure terminal
switch(config)# no hardware profile portmode
Warning: This command will take effect only after saving the configuration and r
eload! Port configurations could get lost when port mode is changed!
switch(config)#

        Configuring the Interface Speed


        Note

        If the interface and transceiver speed is mismatched, the SFP validation failed message is displayed when you enter the show interface ethernet slot/port command. For example, if you insert a 1-Gigabit SFP transceiver into a port without configuring the speed 1000 command, you will get this error. By default, all ports are 10 Gbps.

        Procedure
           Command or ActionPurpose
          Step 1 switch# configure terminal
           

          Enters global configuration mode.

           
          Step 2 switch(config)# interface type slot/port
           

          Enters interface configuration mode for the specified interface. This interface must have a 1-Gigabit Ethernet SFP transceiver inserted into it.

           
          Step 3 switch(config-if)# speed speed
           

          Sets the speed on the interface.

          This command can only be applied to a physical Ethernet interface. The speed argument can be set to one of the following:

          • 10 Mbps

          • 100 Mbps

          • 1 Gbps

          • 10 Gbps

          • automatic

           

          This example shows how to set the speed for a 1-Gigabit Ethernet port: 

          switch# configure terminal
switch(config)# interface ethernet 1/4
switch(config-if)# speed 1000

          Configuring Break-Out 10-Gigabit Interface Speed Ports

          By default, all ports on Cisco Nexus 3132 switches are 40-Gigabit Ethernet. You can break out a 40-Gigabit Ethernet port to four x10-Gigabit Ethernet ports.

          Procedure
             Command or ActionPurpose
            Step 1switch# configure terminal  

            Enters global configuration mode.

             
            Step 2switch(config)# interface type slot/port-range  
            Enters interface configuration mode for the specified interface.
            Note    Interface range is not supported for 40-Gigabit Ethernet interfaces. For example, Eth 1/2-5 is not supported.
             
            Step 3switch(config-if)# speed 10000  

            Sets the speed on the interface to 10-Gigabit per second.

             

            This example shows how to set the speed to 10-Gigabit per second on Ethernet interface 1/2: 

            switch# configure terminal
switch(config)# interface ethernet 1/2
switch(config-if)# speed 10000

            Configuring Break-In 40-Gigabit Ethernet Interface Speed Ports

            You can break in four x 10-Gigabit Ethernet ports to a 40-Gigabit Ethernet port.

            Procedure
               Command or ActionPurpose
              Step 1switch# configure terminal  

              Enters global configuration mode.

               
              Step 2switch(config)# interface type slot/port  
              Enters interface configuration mode for the specified interface.
              Note    The Interface range is supported for 10-Gigabit Ethernet interfaces. For example, Eth 1/2/1-4 is supported.
               
              Step 3switch(config-if)# speed 40000  

              Sets the speed on the interface to 40 Gbps.

               

              This example shows how to set the speed to 40 Gbps on Ethernet interface 1/2/1: 

              switch# configure terminal 
switch(config)# interface ethernet 1/2/1
switch(config-if)# speed 40000

              Switching Between QSFP and SFP+ Ports

              When you break out ports into the 10-GbE mode, you can switch between the first QSFP port and SFP+ ports 1 to 4. Either the first QSFP port or the four SFP+ ports can be active at any time. QSFP is the default port with an interface speed of 40 Gbps.

              When the first QSFP port is in the 40-GbE mode, you cannot switch the port to four SFP+ ports and the first QSFP port will be active until you break out the port into the 10-GbE mode. This is because SFP+ ports do not support the 40-GbE mode.

              Procedure
                 Command or ActionPurpose
                Step 1switch# configure terminal  

                Enters global configuration mode.

                 
                Step 2switch(config)# [no] hardware profile front portmode qsfp | sfp-plus  
                Activates the specified port mode.
                • qsfp—The front panel QSFP port is active
                • sfp-plus—The front panel SFP+ ports 1 to 4 are active

                The no form of this command activates the QSFP port.

                Note    If the first QSFP port speed is 40 Gbps, this command will run, but the SFP+ ports will not become active until after the speed is changed to 10 Gbps.
                 
                Step 3switch(config)# copy running-config startup-config   (Optional)

                Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

                 

                This example shows how to make the SFP+ ports active: 

                switch# configure terminal
switch(config)# hardware profile front portmode sfp-plus
switch(config)# copy running-config startup-config

                This example shows how to make the QSFP port active: 

                switch# configure terminal
switch(config)# no hardware profile front portmode
switch(config)# copy running-config startup-config

                Disabling Link Negotiation

                By default, auto-negotiation is enabled on all 1G SFP+ and 40G QSFP ports and it is disabled on 10G SFP+ ports. Auto-negotiation is by default enabled on all 1G and 10G Base-T ports. It cannot be disabled on 1G and 10G Base-T ports.

                This command is equivalent to the Cisco IOS speed non-negotiate command.

                Starting with Release 6.0(2)U5(1), you can disable auto-negotiation on all 40G interfaces. A new CLI command no system default interface 40g auto-negotation is introduced to disable auto-negotiation across all the 40G interfaces. The new CLI command is only effective on the 40G interfaces and it does not have any effect on 1G or10G interfaces. For CR4 cables, the auto-negotiation configuration has to be identical at both the end devices for the link to come up.


                Note
                The auto-negotiation configuration is not applicable on 10-Gigabit Ethernet ports. When auto-negotiation is configured on a 10-Gigabit port, the following error message is displayed: 
                ERROR: Ethernet1/40: Configuration does not match the port capability
                Procedure
                   Command or ActionPurpose
                  Step 1switch# configure terminal  

                  Enters global configuration mode.

                   
                  Step 2 switch(config)# interface ethernet slot/port  

                  Selects the interface and enters interface mode.

                   
                  Step 3 switch(config-if)# no negotiate auto  

                  Disables link negotiation on the selected Ethernet interface (1-Gigabit port).

                   
                  Step 4 switch(config-if)# negotiate auto   (Optional)

                  Enables link negotiation on the selected Ethernet interface. The default for 1-Gigabit Ethernet ports is enabled.

                  Note   

                  This command is not applicable for 10GBASE-T ports. It should not be used on 10-GBASE-T ports.

                   

                  This example shows how to disable auto-negotiation on a specified Ethernet interface (1-Gigabit port): 

                  switch# configure terminal
switch(config)# interface ethernet 1/1
switch(config-if)# no negotiate auto
switch(config-if)#

                  This example shows how to enable auto-negotiation on a specified Ethernet interface (1-Gigabit port): 

                  switch# configure terminal
switch(config)# interface ethernet 1/5
switch(config-if)# negotiate auto
switch(config-if)#

                  The following example displays the new CLI introduced for global knob for auto-negotiation disable. The system default configuration is system default interface 40g auto-negotiation. 

                   
switch# configure terminal
(config)# no system default interface 40g auto-negotiation
(config)# sh running-config | grep auto-neg
no system default interface 40g auto-negotiation
(config)# sh interface eth1/19 brief
Eth1/19    1   eth  access up      none    40G(D) –
(config)# sh running-config interface eth1/19 all | grep auto
no negotiate auto 
(config)#

                  Disabling SVI Autostate

                  You can configure a SVI to remain active even if no interfaces are up in the corresponding VLAN. This enhancement is called Autostate Disable.

                  When you enable or disable autostate behavior, it is applied to all the SVIs in the switch unless you configure autostate per SVI .


                  Note

                  Autostate behavior is enabled by default.

                  Procedure
                     Command or ActionPurpose
                    Step 1switch# configure terminal  

                    Enters global configuration mode.

                     
                    Step 2switch(config)# feature interface-vlan 

                    Enables the interface-vlan feature.

                     
                    Step 3switch(config)# system default interface-vlan [no] autostate 

                    Configures the system to enable or disable the Autostate default behavior.

                     
                    Step 4switch(config)# interface vlan interface-vlan-number  (Optional)

                    Creates a VLAN interface. The number range is from 1 to 4094.

                     
                    Step 5switch(config-if)# [no] autostate  (Optional)

                    Enables or disables Autostate behavior per SVI.

                     
                    Step 6switch(config)# show interface-vlan interface-vlan  (Optional)

                    Displays the enabled or disabled Autostate behavior of the SVI.

                     
                    Step 7switch(config)# copy running-config startup-config   (Optional)

                    Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

                     

                    This example shows how to disable the systems Autostate default for all the SVIs on the switch:

                    switch# configure terminal
switch(config)# feature interface-vlan
switch(config)# system default interface-vlan no autostate
switch(config)# interface vlan 50
switch(config-if)# no autostate
switch(config)# copy running-config startup-config

                    This example shows how to enable the systems autostate configuration:

                    switch(config)# show interface-vlan 2
Vlan2 is down, line protocol is down, autostate enabled
Hardware is EtherSVI, address is 547f.ee40.a17c
MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec

                    Configuring a Default Interface

                    The default interface feature allows you to clear the existing configuration of multiple interfaces such as Ethernet, loopback, management, VLAN, and port-channel interfaces. All user configuration under a specified interface will be deleted.

                    Procedure
                       Command or ActionPurpose
                      Step 1switch# configure terminal  

                      Enters global configuration mode.

                       
                      Step 2switch(config)# default interface type interface number   Deletes the configuration of the interface and restores the default configuration. The following are the supported interfaces:
                      • ethernet
                      • loopback
                      • mgmt
                      • port-channel
                      • vlan
                       
                      Step 3switch(config)# exit   Exits global configuration mode.  

                      This example shows how to delete the configuration of an Ethernet interface and revert it to its default configuration: 

                      switch# configure terminal
switch(config)# default interface ethernet 1/3
.......Done
switch(config)# exit

                      Configuring the CDP Characteristics

                      You can configure the frequency of Cisco Discovery Protocol (CDP) updates, the amount of time to hold the information before discarding it, and whether or not to send Version-2 advertisements.

                      Procedure
                         Command or ActionPurpose
                        Step 1switch# configure terminal  

                        Enters global configuration mode.

                         
                        Step 2 switch(config)# [no] cdp advertise {v1 | v2 }
                                                  		(Optional)

                        Configures the version to use to send CDP advertisements. Version-2 is the default state.

                        Use the no form of the command to return to its default setting.

                         
                        Step 3 switch(config)# [no] cdp format device-id {mac-address | serial-number | system-name}
                                                  		(Optional)

                        Configures the format of the CDP device ID. The default is the system name, which can be expressed as a fully qualified domain name.

                        Use the no form of the command to return to its default setting.

                         
                        Step 4 switch(config)# [no] cdp holdtime seconds
                                                  		(Optional)

                        Specifies the amount of time a receiving device should hold the information sent by your device before discarding it. The range is 10 to 255 seconds; the default is 180 seconds.

                        Use the no form of the command to return to its default setting.

                         
                        Step 5 switch(config)# [no] cdp timer seconds
                                                  		(Optional)

                        Sets the transmission frequency of CDP updates in seconds. The range is 5 to 254; the default is 60 seconds.

                        Use the no form of the command to return to its default setting.

                         

                        This example shows how to configure CDP characteristics: 

                        switch# configure terminal
switch(config)# cdp timer 50
switch(config)# cdp holdtime 120
switch(config)# cdp advertise v2

                        Enabling or Disabling CDP

                        You can enable or disable CDP for Ethernet interfaces. This protocol works only when you have it enabled on both interfaces on the same link.

                        Procedure
                           Command or ActionPurpose
                          Step 1switch# configure terminal  

                          Enters global configuration mode.

                           
                          Step 2 switch(config)# interface type slot/port
                           

                          Enters interface configuration mode for the specified interface.

                           
                          Step 3 switch(config-if)# cdp enable
                           

                          Enables CDP for the interface.

                          To work correctly, this parameter must be enabled for both interfaces on the same link.

                           
                          Step 4 switch(config-if)# no cdp enable
                           

                          Disables CDP for the interface.

                           

                          This example shows how to enable CDP for an Ethernet port: 

                          switch# configure terminal
switch(config)# interface ethernet 1/4
switch(config-if)# cdp enable

                          This command can only be applied to a physical Ethernet interface.

                          Enabling the Error-Disabled Detection

                          You can enable error-disable (err-disabled) detection in an application. As a result, when a cause is detected on an interface, the interface is placed in an err-disabled state, which is an operational state that is similar to the link-down state.


                          Note

                          Base ports in Cisco Nexus 5500 never get error disabled due to pause rate-limit like in the Cisco Nexus 5020 or 5010 switch.

                          Procedure
                             Command or ActionPurpose
                            Step 1switch# configure terminal  

                            Enters global configuration mode.

                             
                            Step 2switch(config)# errdisable detect cause {all | link-flap | loopback}  

                            Specifies a condition under which to place the interface in an err-disabled state. The default is enabled.

                             
                            Step 3switch(config)# shutdown  

                            Brings the interface down administratively. To manually recover the interface from the err-disabled state, enter this command first.

                             
                            Step 4switch(config)# no shutdown  

                            Brings the interface up administratively and enables the interface to recover manually from the err-disabled state.

                             
                            Step 5switch(config)# show interface status err-disabled  

                            Displays information about err-disabled interfaces.

                             
                            Step 6switch(config)# copy running-config startup-config   (Optional)

                            Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

                             

                            This example shows how to enable the err-disabled detection in all cases: 

                            switch# configure terminal
switch(config)# errdisable detect cause all
switch(config)# shutdown
switch(config)# no shutdown
switch(config)# show interface status err-disabled
switch(config)# copy running-config startup-config

                            Enabling the Error-Disabled Recovery

                            You can specify the application to bring the interface out of the error-disabled (err-disabled) state and retry coming up. It retries after 300 seconds, unless you configure the recovery timer (see the errdisable recovery interval command).

                            Procedure
                               Command or ActionPurpose
                              Step 1switch# configure terminal  

                              Enters global configuration mode.

                               
                              Step 2switch(config)# errdisable recovery cause {all | udld | bpduguard | link-flap | failed-port-state | pause-rate-limit | loopback}  

                              Specifies a condition under which the interface automatically recovers from the err-disabled state, and the device retries bringing the interface up. The device waits 300 seconds to retry. The default is disabled.

                               
                              Step 3switch(config)# show interface status err-disabled 

                              Displays information about err-disabled interfaces.

                               
                              Step 4switch(config)# copy running-config startup-config   (Optional)

                              Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

                               

                              This example shows how to enable err-disabled recovery under all conditions:

                              switch# configure terminal
switch(config)# errdisable recovery cause loopback
switch(config)# show interface status err-disabled
switch(config)# copy running-config startup-config

                              Configuring the Error-Disabled Recovery Interval

                              You can use this procedure to configure the err-disabled recovery timer value. The range is from 30 to 65535 seconds. The default is 300 seconds.

                              Procedure
                                 Command or ActionPurpose
                                Step 1switch# configure terminal  

                                Enters global configuration mode.

                                 
                                Step 2switch(config)# errdisable recovery interval interval  

                                Specifies the interval for the interface to recover from the err-disabled state. The range is from 30 to 65535 seconds. The default is 300 seconds.

                                 
                                Step 3switch(config)# show interface status err-disabled  

                                Displays information about err-disabled interfaces.

                                 
                                Step 4switch(config)# copy running-config startup-config   (Optional)

                                Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

                                 

                                This example shows how to enable err-disabled recovery under all conditions: 

                                switch# configure terminal
switch(config)# errdisable recovery interval 32
switch(config)# show interface status err-disabled
switch(config)# copy running-config startup-config

                                Disabling the Error-Disabled Recovery

                                You can disable recovery of an interface from the err-disabled state.

                                Procedure
                                   Command or ActionPurpose
                                  Step 1switch# configure terminal  

                                  Enters global configuration mode.

                                   
                                  Step 2switch(config)# no errdisable recovery cause {all | udld | bpduguard | link-flap | failed-port-state | pause-rate-limit | loopback} 

                                  Specifies a condition under which the interface reverts back to the default err-disabled state.

                                   
                                  Step 3switch(config)# show interface status err-disabled  (Optional)

                                  Displays information about err-disabled interfaces.

                                   
                                  Step 4switch(config)# copy running-config startup-config   (Optional)

                                  Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

                                   

                                  This example shows how to disable err-disabled recovery:

                                  switch# configure terminal
switch(config)# no errdisable recovery cause loopback
switch(config)# show interface status err-disabled
switch(config)# copy running-config startup-config

                                  Configuring the Debounce Timer

                                  You can enable the debounce timer for Ethernet ports by specifying a debounce time, in milliseconds (ms), or disable the timer by specifying a debounce time of 0. By default, the debounce timer is set to 100 ms, which results in the debounce timer not running.

                                  You can show the debounce times for all of the Ethernet ports by using the show interface debounce command.

                                  Procedure
                                     Command or ActionPurpose
                                    Step 1switch# configure terminal  

                                    Enters global configuration mode.

                                     
                                    Step 2 switch(config)# interface type slot/port
                                     

                                    Enters interface configuration mode for the specified interface.

                                     
                                    Step 3 switch(config-if)# link debounce time milliseconds
                                     

                                    Enables the debounce timer for the amount of time (1 to 5000 ms) specified.

                                    Disables the debounce timer if you specify 0 milliseconds.

                                     

                                    This example shows how to enable the debounce timer and set the debounce time to 1000 ms for an Ethernet interface: 

                                    switch# configure terminal
switch(config)# interface ethernet 3/1
switch(config-if)# link debounce time 1000

                                    This example shows how to disable the debounce timer for an Ethernet interface: 

                                    switch# configure terminal
switch(config)# interface ethernet 3/1
switch(config-if)# link debounce time 0

                                    Configuring the Description Parameter

                                    You can provide textual interface descriptions for the Ethernet ports.

                                    Procedure
                                       Command or ActionPurpose
                                      Step 1switch# configure terminal  

                                      Enters global configuration mode.

                                       
                                      Step 2 switch(config)# interface type slot/port
                                       

                                      Enters interface configuration mode for the specified interface.

                                       
                                      Step 3 switch(config-if)# description test
                                       

                                      Specifies the description for the interface.

                                       

                                      This example shows how to set the interface description to Server 3 interface: 

                                      switch# configure terminal
switch(config)# interface ethernet 1/3
switch(config-if)# description Server 3 Interface

                                      Disabling and Restarting Ethernet Interfaces

                                      You can shut down and restart an Ethernet interface. This action disables all of the interface functions and marks the interface as being down on all monitoring displays. This information is communicated to other network servers through all dynamic routing protocols. When shut down, the interface is not included in any routing updates.

                                      Procedure
                                         Command or ActionPurpose
                                        Step 1switch# configure terminal  

                                        Enters global configuration mode.

                                         
                                        Step 2 switch(config)# interface type slot/port
                                         

                                        Enters interface configuration mode for the specified interface.

                                         
                                        Step 3 switch(config-if)# shutdown
                                         

                                        Disables the interface.

                                         
                                        Step 4 switch(config-if)# no shutdown
                                         

                                        Restarts the interface.

                                         

                                        This example shows how to disable an Ethernet port: 

                                        switch# configure terminal
switch(config)# interface ethernet 1/4
switch(config-if)# shutdown

                                        This example shows how to restart an Ethernet interface: 

                                        switch# configure terminal
switch(config)# interface ethernet 1/4
switch(config-if)# no shutdown

                                        Configuring Downlink Delay

                                        You can operationally enable uplink SFP+ ports before downlink RJ-45 ports after a reload on a Cisco Nexus 3048 switch by delaying enabling the RJ-45 ports in the hardware until the SFP+ ports are enabled.

                                        Procedure
                                           Command or ActionPurpose
                                          Step 1switch# configure terminal  

                                          Enters global configuration mode.

                                           
                                          Step 2 switch(config)# downlink delay enable | disable [timeout time-out]  

                                          Enables or disables downlink delay and configures the timeout.

                                           

                                          This example shows how to enable downlink delay and configure the delay timeout on the switch: 

                                          switch# configure terminal
switch(config)# downlink delay enable timeout 45

                                          Displaying Interface Information

                                          To view configuration information about the defined interfaces, perform one of these tasks:

                                          Command

                                          Purpose

                                          switch# show interface type slot/port

                                          Displays the detailed configuration of the specified interface.

                                          switch# show interface type slot/port capabilities

                                          Displays detailed information about the capabilities of the specified interface. This option is available only for physical interfaces.

                                          switch# show interface type slot/port transceiver

                                          Displays detailed information about the transceiver connected to the specified interface. This option is available only for physical interfaces.

                                          switch# show interface brief

                                          Displays the status of all interfaces.

                                          switch# show interface flowcontrol

                                          Displays the detailed listing of the flow control settings on all interfaces.

                                          The show interface command is invoked from EXEC mode and displays the interface configurations. Without any arguments, this command displays the information for all the configured interfaces in the switch.

                                          This example shows how to display the physical Ethernet interface: 

                                          switch# show interface ethernet 1/1
  Ethernet1/1 is up
  Hardware is 1000/10000 Ethernet, address is 000d.eca3.5f08 (bia 000d.eca3.5f08)
  MTU 1500 bytes, BW 10000000 Kbit, DLY 10 usec,
     reliability 255/255, txload 190/255, rxload 192/255
  Encapsulation ARPA
  Port mode is trunk
  full-duplex, 10 Gb/s, media type is 1/10g
  Input flow-control is off, output flow-control is off
  Auto-mdix is turned on
  Rate mode is dedicated
  Switchport monitor is off
  Last clearing of "show interface" counters never
  5 minute input rate 942201806 bytes/sec, 14721892 packets/sec
  5 minute output rate 935840313 bytes/sec, 14622492 packets/sec
  Rx
    129141483840 input packets 0 unicast packets 129141483847 multicast packets
    0 broadcast packets 0 jumbo packets 0 storm suppression packets
    8265054965824 bytes
    0 No buffer 0 runt 0 Overrun
    0 crc 0 Ignored 0 Bad etype drop
    0 Bad proto drop
  Tx
    119038487241 output packets 119038487245 multicast packets
   0 broadcast packets 0 jumbo packets
    7618463256471 bytes
    0 output CRC 0 ecc
    0 underrun 0 if down drop     0 output error 0 collision 0 deferred
    0 late collision 0 lost carrier 0 no carrier
    0 babble
    0 Rx pause 8031547972 Tx pause 0 reset

                                          This example shows how to display the physical Ethernet capabilities: 

                                          switch# show interface ethernet 1/1 capabilities
Ethernet1/1
  Model:                 734510033
  Type:                  10Gbase-(unknown)
  Speed:                 1000,10000
  Duplex:                full
  Trunk encap. type:     802.1Q
  Channel:               yes
  Broadcast suppression: percentage(0-100)
  Flowcontrol:											rx-(off/on),tx-(off/on)
  Rate mode:             none
  QOS scheduling:        rx-(6q1t),tx-(1p6q0t)
  CoS rewrite:           no
  ToS rewrite:           no
  SPAN:                  yes
  UDLD:                  yes

  MDIX:                  no
  FEX Fabric:            yes

                                          This example shows how to display the physical Ethernet transceiver: 

                                          switch# show interface ethernet 1/1 transceiver
Ethernet1/1
    sfp is present
    name is CISCO-EXCELIGHT
    part number is SPP5101SR-C1
    revision is A
    serial number is ECL120901AV
    nominal bitrate is 10300 MBits/sec
    Link length supported for 50/125mm fiber is 82 m(s)
    Link length supported for 62.5/125mm fiber is 26 m(s)
    cisco id is --
    cisco extended id number is 4

                                          This example shows how to display a brief interface status (some of the output has been removed for brevity): 

                                          switch# show interface brief

--------------------------------------------------------------------------------
Ethernet      VLAN   Type Mode   Status  Reason                   Speed     Port
Interface                                                                   Ch #
--------------------------------------------------------------------------------
Eth1/1        200    eth  trunk  up      none                        10G(D) --
Eth1/2        1      eth  trunk  up      none                        10G(D) --
Eth1/3        300    eth  access down    SFP not inserted            10G(D) --
Eth1/4        300    eth  access down    SFP not inserted            10G(D) --
Eth1/5        300    eth  access down    Link not connected         1000(D) --
Eth1/6        20     eth  access down    Link not connected          10G(D) --
Eth1/7        300    eth  access down    SFP not inserted            10G(D) --
...

                                          This example shows how to display the CDP neighbors: 

                                          switch# show cdp neighbors
Capability Codes: R - Router, T - Trans-Bridge, B - Source-Route-Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater,
                  V - VoIP-Phone, D - Remotely-Managed-Device,
                  s - Supports-STP-Dispute
Device ID              Local Intrfce   Hldtme  Capability  Platform      Port ID
d13-dist-1               mgmt0           148     S I      WS-C2960-24TC  Fas0/9
n5k(FLC12080012)         Eth1/5          8       S I s    N5K-C5020P-BA  Eth1/5

                                          MIBs for Layer 2 Interfaces

                                          MIB

                                          MIB Link

                                          IF-MIB

                                          To locate and download MIBs, go to the following URL:

                                          http:/​/​www.cisco.com/​public/​sw-center/​netmgmt/​cmtk/​mibs.shtml

                                          MAU-MIB

                                          Limited support includes only the following MIB Objects:

                                          • ifMauType (Read-only) GET

                                          • ifMauAutoNegSupported (Read-only) GET

                                          • ifMauTypeListBits (Read-only) GET

                                          • ifMauDefaultType (Read-write) GET-SET

                                          • ifMauAutoNegAdminStatus (Read-write) GET-SET

                                          • ifMauAutoNegCapabilityBits (Read-only) GET

                                          • ifMauAutoNegAdvertisedBits (Read-write) GET-SET