Catalyst 2940 Switch Software Configuration Guide, 12.1(19)EA1
Configuring the Switch Interfaces
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Configuring the Switch Interfaces

Table Of Contents

Configuring the Switch Interfaces

Understanding Interface Types

Access Ports

Trunk Ports

Port-Based VLANs

EtherChannel Port Groups

Connecting Interfaces

Using the Interface Command

Procedures for Configuring Interfaces

Configuring a Range of Interfaces

Configuring and Using Interface-Range Macros

Configuring Ethernet Interfaces

Default Ethernet Interface Configuration

Configuring Interface Speed and Duplex Mode

Configuration Guidelines

Setting the Interface Speed and Duplex Parameters

Configuring Auto-MDIX on an Interface

Adding a Description for an Interface

Monitoring and Maintaining the Interfaces

Monitoring Interface and Controller Status

Clearing and Resetting Interfaces and Counters

Shutting Down and Restarting the Interface


Configuring the Switch Interfaces


This chapter describes the types of interfaces on a Catalyst 2940 switch and how to configure them. The chapter has these sections:

Understanding Interface Types

Using the Interface Command

Configuring Ethernet Interfaces

Monitoring and Maintaining the Interfaces


Note For complete syntax and usage information for the commands used in this chapter, refer to the switch command reference for this release and the online Cisco IOS Interface Command Reference for Cisco IOS Release 12.1.


Understanding Interface Types

This section describes the different types of interfaces supported by the switch with references to chapters that contain more detailed information about configuring these interface types. The rest of the chapter describes configuration procedures for switch ports.

Switch ports are Layer 2-only interfaces associated with a physical port. They are used for managing the physical interface and associated Layer 2 protocols and do not handle routing or bridging. A switch port can be an access port or a trunk port.

You can configure a port as an access port or trunk port or let the Dynamic Trunking Protocol (DTP) operate on a per-port basis to determine if a switch port should be an access port or a trunk port by negotiating with the port on the other end of the link.

Configure switch ports by using the switchport interface configuration commands. For detailed information about configuring access port and trunk port characteristics, see "Configuring VLANs."

These sections describes these types of interfaces:

Access Ports

Trunk Ports

Port-Based VLANs

EtherChannel Port Groups

Connecting Interfaces

Access Ports

An access port belongs to and carries the traffic of only one VLAN (unless it is configured as a voice VLAN port). Traffic is received and sent in native formats with no VLAN tagging. Traffic arriving on an access port is assumed to belong to the VLAN assigned to the port. If an access port receives an 802.1P- or 802.1Q-tagged packet for the VLAN assigned to the port, the packet is forwarded. If the port receives an 802.1P- or 802.1Q-tagged packet for another VLAN, the packet is dropped, the source address is not learned, and the frame is counted in the No destination statistic.

The Catalyst 2940 switch does not support ISL-tagged packets. If the switch receives an ISL-tagged packet, the packet is flooded in the native VLAN of the port on which it was received because the MAC destination address in the ISL-tagged packet is a multicast address.

Two types of access ports are supported:

Static access ports are manually assigned to a VLAN.

VLAN membership of dynamic access ports is learned through incoming packets. By default, a dynamic access port is a member of no VLAN, and forwarding to and from the port is enabled only when the VLAN membership of the port is discovered. Dynamic access ports on the switch are assigned to a VLAN by a VLAN Membership Policy Server (VMPS). The VMPS can be a Catalyst 6000 series switch; the Catalyst 2940 switch does not support the function of a VMPS.

You can also configure an access port with an attached Cisco IP Phone to use one VLAN for voice traffic and another VLAN for data traffic from a device attached to the phone. From more information about voice VLAN ports, see "Configuring VLANs."

Trunk Ports

A trunk port carries the traffic of multiple VLANs and by default is a member of all VLANs in the VLAN database. Only IEEE 802.1Q trunk ports are supported. An IEEE 802.1Q trunk port supports simultaneous tagged and untagged traffic. An 802.1Q trunk port is assigned a default Port VLAN ID (PVID), and all untagged traffic travels on the port default PVID. All untagged traffic and tagged traffic with a NULL VLAN ID are assumed to belong to the port default PVID. A packet with a VLAN ID equal to the outgoing port default PVID is sent untagged. All other traffic is sent with a VLAN tag.

Although by default, a trunk port is a member of every VLAN known to the VTP, you can limit VLAN membership by configuring an allowed list of VLANs for each trunk port. The list of allowed VLANs does not affect any other port but the associated trunk port. By default, all possible VLANs (VLAN ID 1 to 1005) are in the allowed list. A trunk port can only become a member of a VLAN if VTP knows of the VLAN and the VLAN is in the enabled state. If VTP learns of a new, enabled VLAN and the VLAN is in the allowed list for a trunk port, the trunk port automatically becomes a member of that VLAN and traffic is forwarded to and from the trunk port for that VLAN. If VTP learns of a new, enabled VLAN that is not in the allowed list for a trunk port, the port does not become a member of the VLAN, and no traffic for the VLAN is forwarded to or from the port.


Note VLAN 1 cannot be excluded from the allowed list.


For more information about trunk ports, see "Configuring VLANs."

Port-Based VLANs

A VLAN is a switched network that is logically segmented by function, team, or application, without regard to the physical location of the users. For more information about VLANs, see "Configuring VLANs." Packets received on a port are forwarded only to ports that belong to the same VLAN as the receiving port. Network devices in different VLANs cannot communicate with one another without a Layer 3 device to route traffic between the VLANs.

VLAN partitions provide hard firewalls for traffic in the VLAN, and each VLAN has its own MAC address table. A VLAN comes into existence when a local port is configured to be associated with the VLAN, when the VLAN Trunking Protocol (VTP) learns of its existence from a neighbor on a trunk, or when a user creates a VLAN.

To configure normal-range VLANs (VLAN IDs 1 to 1005), use the vlan vlan-id global configuration command to enter config-vlan mode or the vlan database privileged EXEC command to enter VLAN configuration mode. The VLAN configurations for VLAN IDs 1 to 1005 are saved in the VLAN database.

Add ports to a VLAN by using the switchport interface configuration commands:

Identify the interface.

For a trunk port, set trunk characteristics, and if desired, define the VLANs to which it can belong.

For an access port, set and define the VLAN to which it belongs.

EtherChannel Port Groups

EtherChannel port groups provide the ability to treat multiple switch ports as one switch port. These port groups act as a single logical port for high-bandwidth connections between switches or between switches and servers. An EtherChannel balances the traffic load across the links in the channel. If a link within the EtherChannel fails, traffic previously carried over the failed link changes to the remaining links. You can group multiple trunk ports into one logical trunk port or group multiple access ports into one logical access port. Most protocols operate over either single ports or aggregated switch ports and do not recognize the physical ports within the port group. Exceptions are the DTP, the Cisco Discovery Protocol (CDP), the Port Aggregation Protocol (PAgP), and Link Aggregation Control Protocol (LACP) which operate only on physical ports.

When you configure an EtherChannel, you create a port-channel logical interface and assign an interface to the EtherChannel. For Layer 2 interfaces, the logical interface is dynamically created. You manually assign an interface to the EtherChannel by using the channel-group interface configuration command. This command binds the physical and logical ports together. For more information, see "Configuring EtherChannels."

Connecting Interfaces

Devices within a single VLAN can communicate directly through any switch. Ports in different VLANs cannot exchange data without going through a routing device or routed interface.

With a standard Layer 2 switch, ports in different VLANs have to exchange information through a router. In the configuration shown in Figure 9-1, when Host A in VLAN 20 sends data to Host B in VLAN 30, it must go from Host A to the switch, to the router, back to the switch, and then to Host B.

Figure 9-1 Connecting VLANs with Layer 2 Switches

Using the Interface Command

To configure a physical interface (port), use the interface global configuration command to enter interface configuration mode and to specify the interface type, slot, and number.

TypeFast Ethernet (fastethernet or fa) for 10/100 Ethernet or Gigabit Ethernet (gigabitethernet or gi).

SlotThe slot number on the switch (always 0 on this switch).

Port number—The interface number on the switch. The port numbers always begin at 1, starting at the left when facing the front of the switch; for example, fastethernet 0/1, fastethernet 0/2. If there is more than one media type (for example, 10/100 ports and Gigabit Ethernet ports), the port number starts again with the second medium: gigabitethernet 0/1.

You can identify physical interfaces by physically checking the interface location on the switch. You can also use the Cisco IOS show privileged EXEC commands to display information about a specific interface or all the interfaces on the switch. The remainder of this chapter primarily provides physical interface configuration procedures.

This section describes how to configure all types of interfaces and how to configure a range of interfaces:

Procedures for Configuring Interfaces

Configuring a Range of Interfaces

Configuring and Using Interface-Range Macros

Procedures for Configuring Interfaces

These general instructions apply to all interface configuration processes.


Step 1 Enter the configure terminal command at the privileged EXEC prompt:

Switch# configure terminal 
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)# 

Step 2 Enter the interface global configuration command. Identify the interface type and the number of the connector. In these examples, Fast Ethernet interface 0/4 is selected, and Gigabit Ethernet 0/1 is selected:

Switch(config)# interface fastethernet0/4 
Switch(config-if)# 
Switch(config)# interface gigabitethernet0/1 
Switch(config-if)# 


Note You do not need to add a space between the interface type and interface number. In the preceding examples, you can specify either fastethernet 0/4, fa 0/4, or fa0/4; gigabitethernet 0/1, gi 0/1, or gi0/1.


Step 3 Follow each interface command with the interface configuration commands your particular interface requires. The commands you enter define the protocols and applications that will run on the interface. The commands are collected and applied to the interface when you enter another interface command or enter end to return to privileged EXEC mode.

You can also configure a range of interfaces by using the interface range or interface range macro global configuration commands. Interfaces configured in a range must be the same type and must be configured with the same feature options.

Step 4 After you configure an interface, verify its status by using the show privileged EXEC commands listed in the "Monitoring and Maintaining the Interfaces" section.


Enter the show interfaces privileged EXEC command to see a list of all interfaces on or configured for the switch. A report is provided for each interface that the device supports or for the specified interface:

Switch# show interfaces
Vlan1 is up, line protocol is up 
  Hardware is CPU Interface, address is 0003.fd62.8d40 (bia 0003.fd62.8d40)
  Internet address is 172.20.139.142/27
  MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:00, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue :0/40 (size/max)
  5 minute input rate 2000 bits/sec, 4 packets/sec
  5 minute output rate 1000 bits/sec, 2 packets/sec
     2832963 packets input, 214073802 bytes, 0 no buffer
     Received 21170 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 14 ignored
     2120022 packets output, 271900223 bytes, 0 underruns
     0 output errors, 2 interface resets
     0 output buffer failures, 0 output buffers swapped out
FastEthernet0/1 is up, line protocol is up (connected)
  Hardware is Fast Ethernet, address is 0003.fd62.8d41 (bia 0003.fd62.8d41)
  MTU 1500 bytes, BW 100000 Kbit, DLY 1000 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 100Mb/s
  input flow-control is off, output flow-control is off
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue :0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute ouxtput rate 0 bits/sec, 0 packets/sec
     1074142 packets input, 81896024 bytes, 0 no buffer
     Received 922680 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 922675 multicast, 0 pause input
     0 input packets with dribble condition detected
     1547721 packets output, 107609465 bytes, 0 underruns
     0 output errors, 0 collisions, 2 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 PAUSE output
     0 output buffer failures, 0 output buffers swapped out

<output truncated>

Configuring a Range of Interfaces

You can use the interface range global configuration command to configure multiple interfaces with the same configuration parameters. When you enter the interface-range configuration mode, all command parameters that you enter are attributed to all interfaces within that range until you exit this mode.

Beginning in privileged EXEC mode, follow these steps to configure a range of interfaces with the same parameters:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

interface range {port-range | macro macro_name}

Enter interface-range configuration mode by entering the range of interfaces (VLANs or physical ports) to be configured.

You can use the interface range command to configure up to five port ranges or a previously defined macro.

The macro variable is explained in the "Configuring and Using Interface-Range Macros" section.

Each comma-separated port-range must consist of the same port type. You do not need to enter spaces before or after the comma.

When you define a range, the space between the first port and the hyphen is required.

Step 3 

 

You can now use the normal configuration commands to apply the configuration parameters to all interfaces in the range.

Step 4 

end

Return to privileged EXEC mode.

Step 5 

show interfaces [interface-id]

Verify the configuration of the interfaces in the range.

Step 6 

copy running-config startup-config

(Optional) Save your entries in the configuration file.

When using the interface range global configuration command, note these guidelines:

Valid entries for port-range:

vlan vlan-ID - vlan-ID, where VLAN ID is from 1 to 1005

fastethernet slot/{first port} - {last port}, where slot is 0

gigabitethernet slot/{first port} - {last port}, where slot is 0

port-channel port-channel-number - port-channel-number, where port-channel-number is from 1 to 6

You must add a space between the interface numbers and the hyphen when using the interface range command. For example, the command interface range fastethernet 0/1 - 5 is a valid range; the command interface range fastethernet 0/1-5 is not a valid range.

The interface range command works only with VLAN interfaces that have been configured with the interface vlan command (the show running-config privileged EXEC command output shows the configured VLAN interfaces). VLAN interfaces that do not appear by using the show running-config command cannot be used with the interface range command.

All interfaces in a range must be the same type; that is, all Fast Ethernet ports, all Gigabit Ethernet ports, all EtherChannel ports, or VLAN interfaces.

This example shows how to use the interface range global configuration command to enable Fast Ethernet interfaces 0/1 to 0/5:

Switch# configure terminal
Switch(config)# interface range fastethernet0/1 - 5 
Switch(config-if-range)# no shutdown 
Switch(config-if-range)#
*Oct  6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to up
*Oct  6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet0/2, changed state to up
*Oct  6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet0/3, changed state to up
*Oct  6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet0/4, changed state to up
*Oct  6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to up
*Oct  6 08:24:36: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/05, 
changed state to up
*Oct  6 08:24:36: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/3, changed 
state to up
*Oct  6 08:24:36: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/4, changed 
state to up

This example shows how to use a comma to add different interface type strings to the range to enable all Fast Ethernet interfaces in the range 0/1 to 0/3 and Gigabit Ethernet interfaces 0/1:

Switch# configure terminal
Switch(config)# interface range fastethernet0/1 - 3, gigabitethernet0/1
Switch(config-if-range)# no shutdown 
Switch(config-if-range)#
*Oct  6 08:29:28: %LINK-3-UPDOWN: Interface FastEthernet0/1, changed state to up
*Oct  6 08:29:28: %LINK-3-UPDOWN: Interface FastEthernet0/2, changed state to up
*Oct  6 08:29:28: %LINK-3-UPDOWN: Interface FastEthernet0/3, changed state to up
*Oct  6 08:29:28: %LINK-3-UPDOWN: Interface GigabitEthernet0/1, changed state to up
*Oct  6 08:29:29: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/ 1, 
changed state to up
*Oct  6 08:29:29: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/ 2, 
changed state to up
*Oct  6 08:29:29: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/ 3, 
changed state to up

If you enter multiple configuration commands while you are in interface-range mode, each command is executed as it is entered. The commands are not batched together and executed after you exit interface-range mode. If you exit interface-range configuration mode while the commands are being executed, some commands might not be executed on all interfaces in the range. Wait until the command prompt reappears before exiting interface-range configuration mode.

Configuring and Using Interface-Range Macros

You can create an interface-range macro to automatically select a range of interfaces for configuration. Before you can use the macro keyword in the interface range macro global configuration command string, you must use the define interface-range global configuration command to define the macro.

Beginning in privileged EXEC mode, follow these steps to define an interface-range macro:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

define interface-range macro_name interface-range

Define the interface-range macro, and save it in NVRAM.

The macro_name is a 32-character maximum character string.

A macro can contain up to five comma-separated interface ranges. You do not need to enter spaces before or after the comma.

Each interface-range must consist of the same port type.

Step 3 

interface range macro macro_name

Select the interface range to be configured by using the values saved in the interface-range macro called macro_name.

You can now use the normal configuration commands to apply the configuration to all interfaces in the defined macro.

Step 4 

end

Return to privileged EXEC mode.

Step 5 

show running-config | include define

Show the defined interface-range macro configuration.

Step 6 

copy running-config startup-config

(Optional) Save your entries in the configuration file.

Use the no define interface-range macro_name global configuration command to delete a macro.

When using the define interface-range global configuration command, note these guidelines:

Valid entries for interface-range:

vlan vlan-ID - vlan-ID, where VLAN ID is from 1 to 1005

fastethernet slot/{first port} - {last port}, where slot is 0

gigabitethernet slot/{first port} - {last port}, where slot is 0

port-channel port-channel-number - port-channel-number, where port-channel-number is from 1 to 6.

You must add a space between the interface numbers and the hyphen when entering an interface-range. For example, fastethernet 0/1 - 5 is a valid range; fastethernet 0/1-5 is not a valid range.

The VLAN interfaces must have been configured with the interface vlan command. The show running-config privileged EXEC command output shows the configured VLAN interfaces. VLAN interfaces that do not appear by using the show running-config command cannot be used as interface-ranges.

All interfaces in a range must be the same type; that is, all Fast Ethernet ports, all Gigabit Ethernet ports, all EtherChannel ports, or all VLANs, but you can combine multiple interface types in a macro.

This example shows how to define an interface-range macro named enet_list to select Fast Ethernet ports 1 to 4 and to verify the macro configuration:

Switch# configure terminal
Switch(config)# define interface-range enet_list fastethernet0/1 - 4 
Switch(config)# end
Switch# show running-config | include define 
define interface-range enet_list FastEthernet0/1 - 4

This example shows how to create a multiple-interface macro named macro1:

Switch# configure terminal
Switch(config)# define interface-range macro1 gigabitethernet0/1 , fastethernet0/5 - 7
Switch(config)# end
Switch# 

This example shows how to enter interface range configuration mode for the interface-range macro enet_list:

Switch# configure terminal
Switch(config)# interface range macro enet_list 
Switch(config-if-range)# 

This example shows how to delete the interface-range macro enet_list and to verify that it has been deleted.

Switch# configure terminal
Switch(config)# no define interface-range enet_list 
Switch# show run | include define

Configuring Ethernet Interfaces

The switch supports these interface types:

Physical ports—Switch ports, including access and trunk ports

VLANs—Switch virtual interfaces (SVIs)

Port-channels—EtherChannel of interfaces

These sections describe the default interface configuration and the optional features that you can configure on most physical interfaces:

Default Ethernet Interface Configuration

Configuring Interface Speed and Duplex Mode

Configuring Auto-MDIX on an Interface

Adding a Description for an Interface

Default Ethernet Interface Configuration

Table 9-1 shows the Ethernet interface default configuration. For more details on the VLAN parameters listed in the table, see "Configuring VLANs." For details on controlling traffic to the port, see "Configuring Port-Based Traffic Control."

Table 9-1 Default Ethernet Interface Configuration 

Feature
Default Setting

Operating mode

Layer 2.

Allowed VLAN range

VLANs 1 to 1005.

Default VLAN (for access ports)

VLAN 1.

Native VLAN (for 802.1Q trunks)

VLAN 1.

VLAN trunking

Switchport mode dynamic desirable (supports DTP).

Port enable state

All ports are enabled.

Port description

None defined.

Speed

Autonegotiate.

Duplex mode

Autonegotiate.

Flow control

Flow control is set to off for receive and desired for send for Gigabit Ethernet ports.

EtherChannel (PAgP) and Link Aggregation Control Protocol (LACP)

Disabled on all Ethernet ports. See "Configuring EtherChannels."

Broadcast, multicast, and unicast storm control

Disabled.

Protected port

Disabled. See the "Configuring Protected Ports" section.

Port security

Disabled. See the "Default Port Security Configuration" section.

Port Fast

Disabled.

Auto-MDIX

Disabled.


Configuring Interface Speed and Duplex Mode

The 10/100 Ethernet interfaces on the switch operate in 10 or 100 Mbps and in either full- or half- duplex mode. The 10/100/1000 Ethernet interfaces operate at 10, 100, or 1000 Mbps. The Gigabit Ethernet interfaces operates in 10 or 100 Mbps in either full- or half-duplex mode and in 1000 full-duplex mode.

In full-duplex mode, two stations can send and receive at the same time. When packets can flow in both directions simultaneously, effective Ethernet bandwidth doubles to 20 Mbps for 10-Mbps interfaces, to 200 Mbps for Fast Ethernet interfaces, and to 2 Gbps for a Gigabit interface. Full-duplex communication is often an effective solution to collisions, which are major constrictions in Ethernet networks. Normally, 10-Mbps ports operate in half-duplex mode, which means that stations can either receive or send.

You can configure interface speed on Fast Ethernet (10/100-Mbps) and Gigabit Ethernet (10/100/1000-Mbps) interfaces. You can configure duplex mode on any Fast Ethernet interfaces that are not set to autonegotiate.

These sections describe how to configure the interface speed and duplex mode:

Configuration Guidelines

Setting the Interface Speed and Duplex Parameters

Configuration Guidelines

When configuring an interface speed and duplex mode, note these guidelines:

Ethernet ports set to 1000 Mbps should always be set to full duplex.

A Gigabit Ethernet port that does not match the settings of an attached device can lose connectivity and does not generate statistics.

If both ends of the line support autonegotiation, we highly recommend the default setting of autonegotiation.

When connecting an interface to a 100BASE-T device that does not autonegotiate, set the speed to a non-auto value (for example, nonegotiate) and set the duplex mode to full or half to match the device. The speed value and duplex mode must be explicitly set.

When connecting an interface to a Gigabit Ethernet device that does not autonegotiate, disable autonegotiation on the switch and set the duplex and flow control parameters to be compatible with the remote device.

100BASE-FX ports operate only at 100 Mbps and in full-duplex mode.

When Spanning Tree Protocol (STP) is enabled and a port is reconfigured, the switch can take up to 30 seconds to check for loops. The port LED is amber while STP reconfigures.


Caution Changing the interface speed and duplex mode configuration might shut down and re-enable the interface during the reconfiguration.

Setting the Interface Speed and Duplex Parameters

Beginning in privileged EXEC mode, follow these steps to set the speed and duplex mode for a physical interface:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

interface interface-id

Enter interface configuration mode and the physical interface identification.

Step 3 

speed {10 | 100 | 1000 | auto}

Enter the appropriate speed parameter for the interface, or enter auto.

Note The 1000 keyword is available only for 10/100/1000 Mbps ports. 100BASE-FX ports operate only at 100 Mbps.

Step 4 

duplex {auto | full | half}

Enter the duplex parameter for the interface.

Step 5 

end

Return to privileged EXEC mode.

Step 6 

show interfaces interface-id

Display the interface speed and duplex mode configuration.

Step 7 

copy running-config startup-config

(Optional) Save your entries in the configuration file.

Use the no speed and no duplex interface configuration commands to return the interface to the default speed and duplex settings (autonegotiate). To return all interface settings to the defaults, use the default interface interface-id interface configuration command.

This example shows how to set the interface speed to 10 Mbps and the duplex mode to half on Fast Ethernet interface 0/3 and to verify the configuration:

Switch# configure terminal
Switch(config)# interface fastethernet0/3
Switch(config-if)# speed 10
Switch(config-if)# duplex half
Switch(config)# end
Switch# show running-config
Current configuration : 1695 bytes
!
version 12.1
no service pad
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname switch
!
<output truncated>
!
interface FastEthernet0/2
 no ip address
 duplex half
 speed 10
!
<output truncated>

Configuring Auto-MDIX on an Interface

When automatic medium-dependent interface crossover (Auto-MDIX) is enabled on an interface, the interface automatically detects the required cable connection type (straight-through or crossover) and configures the connection appropriately. When connecting switches without the Auto-MDIX feature, you must use straight-through cables to connect to devices such as servers, workstations, or routers and crossover cables to connect to other switches or repeaters. With Auto-MDIX enabled, you can use either type of cable to connect to other devices, and the interface automatically corrects for any incorrect cabling. For more information about cabling requirements, refer to the hardware installation guide.

Auto-MDIX is disabled by default. When you enable Auto-MDIX, you must also set the speed and duplex on the interface to auto in order for the feature to operate correctly. Auto-MDIX is supported on all 10/100 and 10/100/1000 Mbps interfaces. It is not supported on the SFP module interfaces.

Table 9-2 shows the link states that results from Auto-MDIX settings and correct and incorrect cabling.

Table 9-2 Link Conditions and Auto-MDIX Settings 

Local Side Auto-MDIX
Remote Side Auto-MDIX
With Correct Cabling
With Incorrect Cabling

On

On

Link up

Link up

On

Off

Link up

Link up

Off

On

Link up

Link up

Off

Off

Link up

Link down


Beginning in privileged EXEC mode, follow these steps to configure Auto-MDIX on an interface:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode

Step 2 

interface interface-id

Enter interface configuration mode for the physical interface to be configured.

Step 3 

speed auto

Configure the interface to autonegotiate speed with the connected device.

Step 4 

duplex auto

Configure the interface to autonegotiate duplex mode with the connected device.

Step 5 

mdix auto

Enable Auto-MDIX on the interface.

Step 6 

end

Return to privileged EXEC mode.

Step 7 

show controllers ethernet-controller interface-id phy 32

or

show running-config

Verify the operational state of the Auto-MDIX feature on the interface.

Step 8 

copy running-config startup-config

(Optional) Save your entries in the configuration file.

To disable Auto-MDIX, use the no mdix auto interface configuration command.

This example shows how to enable Auto-MDIX on Gigabit Ethernet interface 0/1:

Switch# configure terminal
Switch(config)# interface gigabitethernet0/1
Switch(config-if)# speed auto
Switch(config-if)# duplex auto
Switch(config-if)# mdix auto
Switch(config-if)# end

Adding a Description for an Interface

You can add a description about an interface to help you remember its function. The description appears in the output of these commands: show configuration, show running-config, and show interfaces.

Beginning in privileged EXEC mode, follow these steps to add a description for an interface:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode

Step 2 

interface interface-id

Enter interface configuration mode, and enter the interface for which you are adding a description.

Step 3 

description string

Add a description (up to 240 characters) for an interface.

Step 4 

end

Return to privileged EXEC mode.

Step 5 

show interfaces interface-id description

or

show running-config

Verify your entry.

Step 6 

copy running-config startup-config

(Optional) Save your entries in the configuration file.

Use the no description interface configuration command to delete the description.

This example shows how to add a description on Fast Ethernet interface 0/4 and to verify the description:

Switch# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Switch(config)# interface fastethernet0/4
Switch(config-if)# description Connects to Marketing
Switch(config-if)# end
Switch# show interfaces fastethernet0/4 description
Interface Status         Protocol Description
Fa0/4     up             down     Connects to Marketing

Monitoring and Maintaining the Interfaces

You can perform the tasks in these sections to monitor and maintain interfaces:

Monitoring Interface and Controller Status

Clearing and Resetting Interfaces and Counters

Shutting Down and Restarting the Interface

Monitoring Interface and Controller Status

Commands entered at the privileged EXEC prompt display information about the interface, including the version of the software and the hardware, the controller status, and statistics about the interfaces. Table 9-3 lists some of these interface monitoring commands. (You can display the full list of show commands by using the show ? command at the privileged EXEC prompt.) These commands are fully described in the command reference for this release and in the Cisco IOS Interface Command Reference for Cisco IOS Release 12.1.

Table 9-3 show Commands for Interfaces 

Command
Purpose

show interfaces [interface-id]

Display the status and configuration of all interfaces or a specific interface.

show interfaces [interface-id] capabilities [module {module-number}]

Display the capabilities of an interface. If you do not specify a module, the capabilities for all ports on the switch appear.

show interfaces interface-id status [err-disabled]

Display interface status or a list of interfaces in error-disabled state.

show interfaces [interface-id] switchport

Display administrative and operational status of switching (nonrouting) ports.

show interfaces [interface-id] description

Display the description configured on an interface or all interfaces and the interface status.

show ip interface [interface-id]

Display the usability status of all interfaces configured for IP or the specified interface.

show running-config interface [interface-id]

Display the running configuration in RAM for the interface.

show version

Display the hardware configuration, software version, the names and sources of configuration files, and the boot images.

show controllers ethernet-controller interface-id phy 32

Verify the operational state of the Auto-MDIX feature on the interface.


For examples of the output from commands in Table 9-3, refer to the command reference for this release and to the Cisco IOS Interface Command Reference for Cisco IOS Release 12.1.

Clearing and Resetting Interfaces and Counters

Table 9-4 lists the privileged EXEC mode clear commands that you can use to clear counters and reset interfaces.

Table 9-4 Clear Commands for Interfaces

Command
Purpose

clear counters [interface-id]

Clear interface counters.

clear interface interface-id

Reset the hardware logic on an interface.

clear line [number | console 0 | vty number]

Reset the hardware logic on an asynchronous serial line.


To clear the interface counters shown by the show interfaces privileged EXEC command, use the clear counters privileged EXEC command. The clear counters command clears all current interface counters from the interface unless optional arguments are specified to clear only a specific interface type from a specific interface number.


Note The clear counters privileged EXEC command does not clear counters retrieved by using Simple Network Management Protocol (SNMP), but only those seen with the show interfaces privileged EXEC command output.


This example shows how to clear and reset the counters on Fast Ethernet interface 0/5:

Switch# clear counters fastethernet0/5 
Clear "show interface" counters on this interface [confirm] y 
Switch#
*Sep 30 08:42:55: %CLEAR-5-COUNTERS: Clear counter on interface FastEthernet0/5
by vty1 (171.69.115.10)

Use the clear interface or clear line privileged EXEC command to clear and reset an interface or serial line. Under most circumstances, you do not need to clear the hardware logic on interfaces or serial lines.

This example shows how to clear and reset Fast Ethernet interface 0/5:

Switch# clear interface fastethernet0/5 

Shutting Down and Restarting the Interface

Shutting down an interface disables all functions on the specified interface and marks the interface as unavailable on all monitoring command displays. This information is communicated to other network servers through all dynamic routing protocols. The interface is not mentioned in any routing updates.

Beginning in privileged EXEC mode, follow these steps to shut down an interface:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

interface {vlan vlan-id} | {{fastethernet | gigabitethernet} interface-id} | {port-channel port-channel-number}

Select the interface to be configured.

Step 3 

shutdown

Shut down an interface.

Step 4 

end

Return to privileged EXEC mode.

Step 5 

show running-config

Verify your entry.

Use the no shutdown interface configuration command to restart the interface.

This example shows how to shut down Fast Ethernet interface 0/5:

Switch# configure terminal
Switch(config)# interface fastethernet0/5 
Switch(config-if)# shutdown 
Switch(config-if)#
*Sep 30 08:33:47: %LINK-5-CHANGED: Interface FastEthernet0/5, changed state to 
administratively down

This example shows how to re-enable Fast Ethernet interface 0/5:

Switch# configure terminal
Switch(config)# interface fastethernet0/5 
Switch(config-if)# no shutdown 
Switch(config-if)#
*Sep 30 08:36:00: %LINK-3-UPDOWN: Interface FastEthernet0/5, changed state to up

To verify that an interface is disabled, enter the show interfaces privileged EXEC command. A disabled interface is shown as administratively down in the show interfaces command output