Configuring Layer 2 Interfaces

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:

  • Interface type—All physical Ethernet interfaces use the ethernet keyword.

  • Slot number:

    • Slot 1 includes all the fixed ports.

    • Slot 2 includes the ports on the upper expansion module (if populated).

    • Slot 3 includes the ports on the lower expansion module (if populated).

    • Slot 4 includes the ports on the lower expansion module (if populated).

  • Port number— Port number within the group.

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.

About 40-Gbps Interface Speed

You can enable 40-Gigabits per second (Gbps) speed on up to 12 interfaces. You enable 40-Gbps speed on the first port of a group of four adjacent ports. For example, you enable 40-Gbps speed on port 1 of port group 1-4, port 5 of port group 5-8, and port 9 of port group 9-12, and so on. The 40-Gbps port numbering is Ethernet interface 1/1, 1/5, 1/9, 1/13, 1/17, and so on.

The configuration is applied to the first port, not on the remaining three ports in the group. The remaining ports act like the ports without an enhanced small form-factor pluggable (SFP+) transceiver inserted. The configuration takes effect immediately. You do not need to reload the switch.

An SFP+ transceiver security check is performed only on the first port of the group.

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.

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.

MTU Configuration

The 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.

You can configure an MTU size of up to 9216 bytes on management interfaces. The change in configuration might trigger a temporary link flap at the end device.

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.

Guidelines and Limitations for Layer 2 Interfaces

  • 40-Gbps Ethernet interfaces do not support the following features:

    • Switched Port Analyzer (SPAN)

    • Encapsulated Remote Switched Port Analyzer (ERSPAN)

    • Warp SPAN

    • Private Virtual Local Area Network (PVLAN)

    • Active buffer monitoring

    • Latency monitoring

    • Link level flow control

    • Precession Time Protocol (PTP)

    • Image downgrade after 40-Gbps interface configuration

    • Configuration rollback

  • If you set the 40-Gbps interface speed on an interface and the link is up, the CLI shows the first port as up and the remaining three ports as down. If any of the four links are down, the CLI shows all of the links as down.

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.

SUMMARY STEPS

  1. switch# configure terminal
  2. switch(config)# feature udld
  3. switch(config)# no feature udld
  4. switch(config)# show udld global
  5. switch(config)# interface type slot/port
  6. switch(config-if)# udld {enable | disable | aggressive}
  7. switch(config-if)# show udld interface

DETAILED STEPS

  Command or Action Purpose

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.

Example

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

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.

SUMMARY STEPS

  1. switch# configure terminal
  2. switch(config)# interface type slot/port
  3. switch(config-if)# speed speed

DETAILED STEPS

  Command or Action Purpose

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

Example

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 40-Gigabit Interface Speed

Before you begin

To achieve 40-Gbps port speed, each of the four ports in an adjacent port group must have a 10-Gbps SFP installed. All four SFP+ must be capable of 10-Gbps speed and must be the same type of port. By default, all ports are 10-Gbps ports.

SUMMARY STEPS

  1. switch# configure terminal
  2. switch(config)# interface type slot/port-range
  3. switch(config-if-rang)# shut
  4. switch(config-if-rang)# exit
  5. switch(config-if)# interface type slot/port
  6. switch(config-if)# speed 40000
  7. switch(config-if)# no shut

DETAILED STEPS

  Command or Action Purpose

Step 1

switch# configure terminal

Enters global configuration mode.

Step 2

switch(config)# interface type slot/port-range

Enters interface configuration mode for the specified range of interfaces.

Step 3

switch(config-if-rang)# shut

Shuts down the range of interfaces that you specified.

Step 4

switch(config-if-rang)# exit

Exits the current configuration mode.

Step 5

switch(config-if)# interface type slot/port

Enters interface configuration mode for the interface. You specify the first port in the four adjacent port group to configure that port with 40-Gbps speed. For example, you specify interface 1/1, which is the first port in port group 1/1 through 1/4, to configure that port with 40-Gbps speed.

Note

 
All four adjacent ports must have 10-Gbps Ethernet SFP transceivers installed.

Step 6

switch(config-if)# speed 40000

Sets the speed on the interface for 40 Gbps.

Step 7

switch(config-if)# no shut

Brings up the range of interfaces.

Example

This example shows how to set the speed to 40 Gbps on Ethernet interface 1/33: 

switch# configure terminal
switch(config)# interface ethernet 1/33-36
switch(config-if-rang)# shut
switch(config-if-rang)# exit
switch(config)# interface ethernet 1/33
switch(config-if)# speed 40000
switch(config-if)# no shut

Disabling Link Negotiation

You can disable link negotiation using the no negotiate auto command. By default, auto-negotiation is enabled on 1-Gigabit ports and disabled on 10-Gigabit ports. The no negotiate auto command is supported on 100M port with full duplex setting.

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


Note
Auto negotiation configuration is not applicable on 10-Gigabit 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

SUMMARY STEPS

  1. switch# configure terminal
  2. switch(config)# interface ethernet slot/port
  3. switch(config-if)# no negotiate auto
  4. (Optional) switch(config-if)# negotiate auto

DETAILED STEPS

  Command or Action Purpose

Step 1

switch# 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

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

(Optional)

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

Note

 

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

Example

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)#

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.

SUMMARY STEPS

  1. switch# configure terminal
  2. switch(config)# feature interface-vlan
  3. switch(config)# system default interface-vlan [no] autostate
  4. (Optional) switch(config)# interface vlan interface-vlan-number
  5. (Optional) switch(config-if)# [no] autostate
  6. (Optional) switch(config)# show interface-vlan interface-vlan
  7. (Optional) switch(config)# copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

switch# configure terminal

Enters global configuration mode.

Step 2

switch(config)# feature interface-vlan

Enables the interface-vlan feature.

Step 3

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

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

Step 4

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

(Optional)

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

Step 5

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

(Optional)

Enables or disables Autostate behavior per SVI.

Step 6

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

(Optional)

Displays the enabled or disabled Autostate behavior of the SVI.

Step 7

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

(Optional)

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

Example

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 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.

SUMMARY STEPS

  1. switch# configure terminal
  2. (Optional) switch(config)# [no] cdp advertise {v1 | v2 }
  3. (Optional) switch(config)# [no] cdp format device-id {mac-address | serial-number | system-name}
  4. (Optional) switch(config)# [no] cdp holdtime seconds
  5. (Optional) switch(config)# [no] cdp timer seconds

DETAILED STEPS

  Command or Action Purpose

Step 1

switch# configure terminal

Enters global configuration mode.

Step 2

(Optional) 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

(Optional) 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

(Optional) 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

(Optional) 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.

Example

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.

SUMMARY STEPS

  1. switch# configure terminal
  2. switch(config)# interface type slot/port
  3. switch(config-if)# cdp enable
  4. switch(config-if)# no cdp enable

DETAILED STEPS

  Command or Action Purpose

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.

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.

Example

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.

SUMMARY STEPS

  1. switch# configure terminal
  2. switch(config)# errdisable detect cause {all | link-flap | loopback}
  3. switch(config)# shutdown
  4. switch(config)# no shutdown
  5. switch(config)# show interface status err-disabled
  6. (Optional) switch(config)# copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

switch# configure terminal

Enters global configuration mode.

Step 2

switch(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 3

switch(config)# shutdown

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

Step 4

switch(config)# no shutdown

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

Step 5

switch(config)# show interface status err-disabled

Displays information about err-disabled interfaces.

Step 6

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

(Optional)

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

Example

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).

SUMMARY STEPS

  1. switch# configure terminal
  2. switch(config)# errdisable recovery cause {all | udld | bpduguard | link-flap | failed-port-state | pause-rate-limit | loopback}
  3. switch(config)# show interface status err-disabled
  4. (Optional) switch(config)# copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

switch# configure terminal

Enters global configuration mode.

Step 2

switch(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 3

switch(config)# show interface status err-disabled

Displays information about err-disabled interfaces.

Step 4

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

(Optional)

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

Example

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.

SUMMARY STEPS

  1. switch# configure terminal
  2. switch(config)# errdisable recovery interval interval
  3. switch(config)# show interface status err-disabled
  4. (Optional) switch(config)# copy running-config startup-config

DETAILED STEPS

  Command or Action Purpose

Step 1

switch# configure terminal

Enters global configuration mode.

Step 2

switch(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 3

switch(config)# show interface status err-disabled

Displays information about err-disabled interfaces.

Step 4

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

(Optional)

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

Example

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

Configuring the Description Parameter

You can provide textual interface descriptions for the Ethernet ports.

SUMMARY STEPS

  1. switch# configure terminal
  2. switch(config)# interface type slot/port
  3. switch(config-if)# description test

DETAILED STEPS

  Command or Action Purpose

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.

Step 3

switch(config-if)# description test

Specifies the description for the interface.

Example

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.

SUMMARY STEPS

  1. switch# configure terminal
  2. switch(config)# interface type slot/port
  3. switch(config-if)# shutdown
  4. switch(config-if)# no shutdown

DETAILED STEPS

  Command or Action Purpose

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.

Step 3

switch(config-if)# shutdown

Disables the interface.

Step 4

switch(config-if)# no shutdown

Restarts the interface.

Example

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 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.


Note

The link debounce feature is available for 10G and 40G interfaces only.

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

SUMMARY STEPS

  1. switch# configure terminal
  2. switch(config)# interface type slot/port
  3. switch(config-if)# link debounce time milliseconds

DETAILED STEPS

  Command or Action Purpose

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.

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.

Example

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

Verifying the Layer 2 Interfaces Configuration

Use one of the following commands to verify the configuration:

Command

Purpose

show interface ethernet slot/port brief

Displays the Layer 2 interface operational status.

Note

 

If you have 40-Gbps interface speed set on an interface and the link is up, the CLI shows the first port as up and the remaining three ports as down. If any one of the four links are down, the CLI shows all of the links as down.

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

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.

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