Cisco Nexus 5000 Series NX-OS Software Configuration Guide
Configuring Ethernet Interfaces
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Configuring Ethernet Interfaces

Table Of Contents

Configuring Ethernet Interfaces

Information About Ethernet Interfaces

About the Interface Command

About the Unidirectional Link Detection Parameter

UDLD Overview

Default UDLD Configuration

UDLD Aggressive and Nonaggressive Modes

About Interface Speed

About the Cisco Discovery Protocol

Default CDP Configuration

About the Debounce Timer Parameters

About MTU Configuration

Configuring Ethernet Interfaces

Configuring the UDLD Mode

Configuring Interface Speed

Configuring the Cisco Discovery Protocol

Configuring the CDP Characteristics

Enabling or Disabling CDP

Configuring the Debounce Timer

Configuring the Description Parameter

Disabling and Restarting Ethernet Interfaces

Displaying Interface Information

Default Physical Ethernet Settings


Configuring Ethernet Interfaces


This section describes the configuration of the Ethernet interfaces on a Cisco Nexus 5000 Series switch. It includes the following sections:

Information About Ethernet Interfaces

Configuring Ethernet Interfaces

Displaying Interface Information

Information About Ethernet Interfaces

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

The Ethernet interfaces also support Fibre Channel over Ethernet (FCoE). FCoE allows the physical Ethernet link to carry both Ethernet and Fibre Channel traffic. For additional information, see Chapter 29, "Configuring FCoE" and Chapter 30, "Configuring Virtual Interfaces."

On a Cisco Nexus 5000 Series switch, the Ethernet interfaces are enabled by default.

This section includes the following topics:

About the Interface Command

About the Unidirectional Link Detection Parameter

About Interface Speed

About the Cisco Discovery Protocol

About the Debounce Timer Parameters

About MTU Configuration

About the 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).

Port number

Port number within the group.

The interface numbering convention is extended to support use with a Cisco Nexus 2000 Series Fabric Extender as follows:

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

Chassis ID is an optional entry to address 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 via the interface. The chassis ID ranges from 100 to 199.

About the Unidirectional Link Detection Parameter

This section includes the following topics:

UDLD Overview

Default UDLD Configuration

UDLD Aggressive and Nonaggressive Modes

UDLD Overview

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, as long as 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 5000 Series switch 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.


Note By default, UDLD is locally disabled on copper LAN ports to avoid sending unnecessary control traffic on this type of media.


Figure 5-1 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 5-1 Unidirectional Link

Default UDLD Configuration

Table 5-1 shows the default UDLD configuration.

Table 5-1 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
Disabled on all Ethernet 10/100 and 1000BASE-TX LAN ports

For information on configuring the UDLD for the device and its port, see the "Configuring the UDLD Mode" section.

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.

About Interface Speed

A Cisco Nexus 5000 Series switch has a number of fixed 10-Gigabit ports, each equipped with SFP+ interface adapters. The Cisco Nexus 5010 switch has 20 fixed ports, the first 8 of which are switchable 1-Gigabit and 10-Gigabit ports. The Cisco Nexus 5020 switch has 40 fixed ports, the first 16 of which are switchable 1-Gigabit and 10-Gigabit ports.

About 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 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

Table 5-2 shows the default CDP configuration.

Table 5-2 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


About the Debounce Timer Parameters

The port debounce time is the amount of time that an interface waits to notify the supervisor of a link going down. During this time, the interface waits to see if the link comes back up. The wait period is a time when traffic is stopped.

You can enable the debounce timer for each interface and specify the delay time in milliseconds.


Caution When you enable the port debounce timer the link up and link down detections are delayed, resulting in a loss of traffic during the debounce period. This situation might affect the convergence and reconvergence of some protocols.

About MTU Configuration

A per-physical Ethernet interface maximum transmission unit (MTU) is not supported. Instead, MTU is set according to the QoS classes. You modify MTU by setting Policy and Class maps. See Chapter 31, "Configuring QoS" for more details.

When you show the interface settings, an MTU of 1500 is displayed for physical Ethernet interfaces and a receive data field size of 2112 is displayed for Fibre Channel interfaces.

Configuring Ethernet Interfaces

This section shows how to configure Ethernet interfaces. It includes the following topics:

Configuring the UDLD Mode

Configuring Interface Speed

Configuring the Cisco Discovery Protocol

Configuring the Debounce Timer

Configuring the Description Parameter

Disabling and Restarting 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.


To configure the UDLD mode, perform this task:

 
Command
Purpose

Step 1 

switch# configure terminal

Enters configuration mode.

Step 2 

switch(config)# feature udld

Enables UDLD for the device.

 

switch(config)# no feature udld

Disables UDLD for the device.

Step 3 

switch(config)# show udld global

Displays the UDLD status for the device.

Step 4 

switch(config)# interface ethernet slot/port

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

Step 5 

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

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

Step 6 

switch(config-if)# show udld interface

Displays the UDLD status for the interface.

This example shows how to enable the 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 Interface Speed

The first 8 ports of a Cisco Nexus 5010 switch and the first 16 ports of a Cisco Nexus 5020 switch are switchable 1-Gigabit and 10-Gigabit ports. The default interface speed is 10-Gigabit. To configure these ports for 1-Gigabit Ethernet, insert a 1-Gigabit Ethernet SFP transceiver into the applicable port and then set its speed with the speed command.

To configure a 1-Gigabit Ethernet port, perform this task:

 
Command
Purpose

Step 1 

switch# configure terminal

Enters 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.

The following 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  

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


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 Gigabits.


Configuring the Cisco Discovery Protocol

This section shows how to configure the Cisco Discovery Protocol (CDP). It includes the following topics:

Configuring the CDP Characteristics

Enabling or Disabling CDP

Configuring the CDP Characteristics

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

To configure CDP characteristics for an interface, perform this task:

 
Command
Purpose

Step 1 

switch# configure terminal

Enters configuration mode.

Step 2 

switch(config)# cdp advertise {v1 | v2 }

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

Step 3 

switch(config)# 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.

Step 4 

switch(config)# 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.

Step 5 

switch(config)# 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 CDP commands to return to the default settings.

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.

To enable or disable CDP for an interface, perform this task:

 
Command
Purpose

Step 1 

switch# configure terminal

Enters 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.

switch(config-if)# no cdp enable

Disables CDP for the interface.

The following 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.

Configuring the Debounce Timer

You can enable the debounce timer for Ethernet ports by specifying a debounce time (in milliseconds) or disable the timer by specifying a debounce time of 0.

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

To enable or disable the debounce timer, perform this task:

 
Command
Purpose

Step 1 

switch# configure terminal

Enters 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 milliseconds) 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 milliseconds for an Ethernet interface:

switch# configure terminal  
switch(config)# interface ethernet 1/4  
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 1/4  
switch(config-if)# link debounce time 0  

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

Configuring the Description Parameter

To provide textual interface descriptions for the Ethernet ports, perform this task:

 
Command
Purpose

Step 1 

switch# configure terminal 

Enters 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.

To disable an interface, perform this task:

 
Command
Purpose

Step 1 

switch# configure terminal

Enters 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.

The following example shows how to disable an Ethernet port:

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

To restart an interface, perform this task:

Command
Purpose

switch(config-if)# no shutdown

Restarts the interface.


The following example shows how to restart an Ethernet interface:

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

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 only available for physical interfaces

switch# show interface type slot/port transceiver

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

switch# show interface brief

Displays the status of all interfaces.

switch# show interface debounce

Displays the debounce 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.

The following 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 

The following 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 
  Link Debounce:         yes 
  Link Debounce Time:    yes 
  MDIX:                  no 
  FEX Fabric:            yes 

The following 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 

The following 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) -- 
... 

The following example shows how to display the link debounce status (some of the output has been removed for brevity):

switch# show interface debounce  
 
-------------------------------------------------------------------------------- 
Port          Debounce time   Value(ms) 
-------------------------------------------------------------------------------- 
... 
Eth1/1        enable               100 
Eth1/2        enable               100 
Eth1/3        enable               100 
... 

The following 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 


Note For Release 4.0(1a)N1(1), the default value of the device ID field for CDP advertisement has been changed from the chassis serial number to the hostname and serial number, as in the example above.


Default Physical Ethernet Settings

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

Parameter
Default Setting

Debounce

Enable, 100 milliseconds

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. See Chapter 31, "Configuring QoS," for additional information.