Configuring Interfaces
Download this chapter
Configuring InterfacesConfiguring Interfaces
 Feedback

Table Of Contents

Configuring Interfaces

Understanding Interface Configuration

Using the Interface Command

Configuring a Range of Interfaces

Defining and Using Interface-Range Macros

Configuring Optional Interface Features

Configuring Ethernet Interface Speed and Duplex Mode

Speed and Duplex Mode Configuration Guidelines

Configuring the Ethernet Interface Speed

Setting the Interface Duplex Mode

Configuring Link Negotiation on Gigabit Ethernet Ports

Displaying the Speed and Duplex Mode Configuration

Configuring Jumbo Frame Support

Understanding Jumbo Frame Support

Configuring MTU Sizes

Configuring IEEE 802.3x Flow Control

Configuring the Port Debounce Timer

Adding a Description for an Interface

Understanding Online Insertion and Removal

Monitoring and Maintaining Interfaces

Monitoring Interface Status

Clearing Counters on an Interface

Resetting an Interface

Shutting Down and Restarting an Interface

Checking the Cable Status Using the TDR


Configuring Interfaces

This chapter describes how to configure interfaces in Cisco IOS Software Release 12.2SX. This chapter consists of these sections:

•Understanding Interface Configuration

•Using the Interface Command

•Configuring a Range of Interfaces

•Defining and Using Interface-Range Macros

•Configuring Optional Interface Features

•Understanding Online Insertion and Removal

•Monitoring and Maintaining Interfaces

•Checking the Cable Status Using the TDR

Note For complete syntax and usage information for the commands used in this chapter, see these publications:

•The Cisco IOS Software Releases 12.2SX Command References at this URL:

http://www.cisco.com/en/US/docs/ios/mcl/122sx_mcl.html

•The Release 12.2 publications at this URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/index.htm

Understanding Interface Configuration

Many features in the software are enabled on a per-interface basis. When you enter the interface command, you must specify the following information:

•Interface type:

–Fast Ethernet (use the fastethernet keyword)

–Gigabit Ethernet (use the gigabitethernet keyword)

–10-Gigabit Ethernet (use the tengigabitethernet keyword)

Note For WAN interfaces, see the configuration note for the WAN module.

•Slot number—The slot in which the module is installed. On switches supported by Cisco IOS Software Release 12.2SX, slots are numbered starting with 1, from top to bottom.

•Port number—The physical port number on the module. On switches supported by Cisco IOS Software Release 12.2SX, the port numbers always begin with 1. When facing the rear of the switch, ports are numbered from the left to the right.

You can identify ports from the physical location. You also can use show commands to display information about a specific port, or all the ports.

Using the Interface Command

Note You use the commands described in this section to configure both physical ports and logical interfaces.

These procedures apply to all interface configuration processes. Begin the interface configuration process in global configuration mode. To use the interface command, follow these steps:

Step 1 Enter the configure terminal command at the privileged EXEC prompt to enter global configuration mode: 

Router# configure terminal 

Enter configuration commands, one per line.  End with CNTL/Z.

Router(config)#

Step 2 In the global configuration mode, enter the interfaces command. Identify the interface type and the number of the connector or interface card.

The following example shows how to select Fast Ethernet, slot 5, interface 1: 

Router(config)# interfaces fastethernet 5/1 

Router(config-if)#

Step 3 Enter the show interfaces EXEC command to see a list of all interfaces that are installed. A report is provided for each interface that the device supports, as shown in this display: 

Router# show interfaces fastethernet 5/48 

FastEthernet5/48 is up, line protocol is up 

  Hardware is C6k 100Mb 802.3, address is 0050.f0ac.3083 (bia 0050.f0ac.3083)

  Internet address is 172.20.52.18/27

  MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, 

     reliability 255/255, txload 1/255, rxload 1/255

  Encapsulation ARPA, loopback not set

  Keepalive set (10 sec)

  Half-duplex, 100Mb/s

  ARP type: ARPA, ARP Timeout 04:00:00

  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 1000 bits/sec, 1 packets/sec

  5 minute output rate 1000 bits/sec, 1 packets/sec

     4834677 packets input, 329545368 bytes, 0 no buffer

     Received 4796465 broadcasts, 0 runts, 0 giants, 0 throttles

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

     0 input packets with dribble condition detected

     51926 packets output, 15070051 bytes, 0 underruns

     0 output errors, 2 collisions, 2 interface resets

     0 babbles, 0 late collision, 0 deferred

     0 lost carrier, 0 no carrier

     0 output buffer failures, 0 output buffers swapped out

Router#

Step 4 Enter the show hardware EXEC command to see a list of the system software and hardware: 

Router# show hardware 

Cisco Internetwork Operating System Software 

IOS (tm) c6sup2_rp Software (c6sup2_rp-JSV-M), Version 12.1(5c)EX, EARLY DEPLOY)

Synced to mainline version: 12.1(5c)

TAC:Home:Software:Ios General:CiscoIOSRoadmap:12.1

Copyright (c) 1986-2001 by cisco Systems, Inc.

Compiled Wed 28-Mar-01 17:52 by hqluong

Image text-base: 0x30008980, data-base: 0x315D0000


ROM: System Bootstrap, Version 12.1(3r)E2, RELEASE SOFTWARE (fc1)

BOOTFLASH: c6sup2_rp Software (c6sup2_rp-JSV-M), Version 12.1(5c)EX, EARLY DEPL)


Router uptime is 2 hours, 55 minutes

System returned to ROM by power-on (SP by power-on)

Running default software


cisco Catalyst 6000 (R7000) processor with 114688K/16384K bytes of memory.

Processor board ID SAD04430J9K

R7000 CPU at 300Mhz, Implementation 39, Rev 2.1, 256KB L2, 1024KB L3 Cache

Last reset from power-on

Bridging software.

X.25 software, Version 3.0.0.

SuperLAT software (copyright 1990 by Meridian Technology Corp).

TN3270 Emulation software.

1 Virtual Ethernet/IEEE 802.3  interface(s)

48 FastEthernet/IEEE 802.3 interface(s)

2 Gigabit Ethernet/IEEE 802.3 interface(s)

381K bytes of non-volatile configuration memory.


16384K bytes of Flash internal SIMM (Sector size 512K).

Configuration register is 0x2


Router#

Step 5 To begin configuring Fast Ethernet port 5/5, enter the interface keyword, interface type, and slot number/port number at the privileged EXEC prompt, as shown in the following example: 

Router# configure terminal 

Enter configuration commands, one per line.  End with CNTL/Z.

Router(config)# interface fastethernet 5/5 

Router(config-if)#

Note You do not need to add a space between the interface type and interface number. For example, in the preceding line you can specify either fastethernet 5/5 or fastethernet5/5.

Step 6 After each interface command, enter 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 command until you enter another interface command or press Ctrl-Z to get out of interface configuration mode and return to privileged EXEC mode.

Step 7 After you configure an interface, check its status by using the EXEC show commands listed in "Monitoring and Maintaining Interfaces" section.

Configuring a Range of Interfaces

The interface-range configuration mode allows you to configure multiple interfaces with the same configuration parameters. After you enter the interface-range configuration mode, all command parameters you enter are attributed to all interfaces within that range until you exit out of the interface-range configuration mode.

To configure a range of interfaces with the same configuration, perform this task:

Command
Purpose

Router(config)# [no] interface range {{vlan vlan_ID - vlan_ID [, vlan vlan_ID - vlan_ID]} | {type1 slot/port - port [, type1 slot/port - port]} | {macro_name [, macro_name]}}

Selects the range of interfaces to be configured.

1 type = fastethernet, gigabitethernet, or tengigabitethernet


When configuring a range of interfaces, note the following information:

•For information about macros, see the "Defining and Using Interface-Range Macros" section.

•You can enter up to five comma-separated ranges.

•You are not required to enter spaces before or after the comma.

•You do not need to add a space between the interface numbers and the dash when using the interface range command.

•The no interface range command supports VLAN interfaces.

•The interface range command supports VLAN interfaces for which Layer 2 VLANs have not been created with the interface vlan command.

Note The link state messages (LINK-3-UPDOWN and LINEPROTO-5-UPDOWN) are disabled by default. Enter the logging event link status command on each interface where you want the messages enabled.

This example shows how to reenable all Fast Ethernet ports 5/1 to 5/5: 

Router(config)# interface range fastethernet 5/1 - 5 

Router(config-if)# no shutdown 

Router(config-if)#

*Oct  6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/1, changed state to up

*Oct  6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/2, changed state to up

*Oct  6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/3, changed state to up

*Oct  6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/4, changed state to up

*Oct  6 08:24:35: %LINK-3-UPDOWN: Interface FastEthernet5/5, changed state to up

*Oct  6 08:24:36: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet5/

5, changed state to up

*Oct  6 08:24:36: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet5/

3, changed state to up

*Oct  6 08:24:36: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet5/

4, changed state to up

Router(config-if)#

This example shows how to use a comma to add different interface type strings to the range to reenable all Fast Ethernet ports in the range 5/1 to 5/5 and both Gigabit Ethernet ports (1/1 and 1/2): 

Router(config-if)# interface range fastethernet 5/1 - 5, gigabitethernet 1/1 - 2 

Router(config-if)# no shutdown 

Router(config-if)#

*Oct  6 08:29:28: %LINK-3-UPDOWN: Interface FastEthernet5/1, changed state to up

*Oct  6 08:29:28: %LINK-3-UPDOWN: Interface FastEthernet5/2, changed state to up

*Oct  6 08:29:28: %LINK-3-UPDOWN: Interface FastEthernet5/3, changed state to up

*Oct  6 08:29:28: %LINK-3-UPDOWN: Interface FastEthernet5/4, changed state to up

*Oct  6 08:29:28: %LINK-3-UPDOWN: Interface FastEthernet5/5, changed state to up

*Oct  6 08:29:28: %LINK-3-UPDOWN: Interface GigabitEthernet1/1, changed state to

 up

*Oct  6 08:29:28: %LINK-3-UPDOWN: Interface GigabitEthernet1/2, changed state to

 up

*Oct  6 08:29:29: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet5/

5, changed state to up

*Oct  6 08:29:29: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet5/

3, changed state to up

*Oct  6 08:29:29: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet5/

4, changed state to up

Router(config-if)#

If you enter multiple configuration commands while you are in interface-range configuration mode, each command is executed as it is entered (they are not batched together and executed after you exit interface-range configuration mode).

If you exit interface-range configuration mode while the commands are being executed, some commands may not be executed on all interfaces in the range. Wait until the command prompt reappears before exiting interface-range configuration mode.

Defining and Using Interface-Range Macros

You can define 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 command string, you must define the macro.

To define an interface-range macro, perform this task:

Command
Purpose

Router(config)# define interface-range macro_name {vlan vlan_ID - vlan_ID} | {type1 slot/port - port} [, {type1 slot/port - port}]

Defines the interface-range macro and save it in NVRAM.

Router(config)# no define interface-range macro_name

Deletes a macro.

1 type = fastethernet, gigabitethernet, or tengigabitethernet


This example shows how to define an interface-range macro named enet_list to select Fast Ethernet ports 5/1 through 5/4: 

Router(config)# define interface-range enet_list fastethernet 5/1 - 4

To show the defined interface-range macro configuration, perform this task:

Command
Purpose

Router# show running-config

Shows the defined interface-range macro configuration.


This example shows how to display the defined interface-range macro named enet_list: 

Router# show running-config | include define 

define interface-range enet_list FastEthernet5/1 - 4

Router#

To use an interface-range macro in the interface range command, perform this task:

Command
Purpose

Router(config)# interface range macro macro_name

Selects the interface range to be configured using the values saved in a named interface-range macro.


This example shows how to change to the interface-range configuration mode using the interface-range macro enet_list: 

Router(config)# interface range macro enet_list 

Router(config-if)#

Configuring Optional Interface Features

These sections describe optional interface features:

•Configuring Ethernet Interface Speed and Duplex Mode

•Configuring Jumbo Frame Support

•Configuring IEEE 802.3x Flow Control

•Configuring the Port Debounce Timer

•Adding a Description for an Interface

Configuring Ethernet Interface Speed and Duplex Mode

These sections describe how to configure Ethernet port speed and duplex mode:

•Speed and Duplex Mode Configuration Guidelines

•Configuring the Ethernet Interface Speed

•Setting the Interface Duplex Mode

•Configuring Link Negotiation on Gigabit Ethernet Ports

•Displaying the Speed and Duplex Mode Configuration

Speed and Duplex Mode Configuration Guidelines

You usually configure Ethernet port speed and duplex mode parameters to auto and allow ports to negotiate the speed and duplex mode. If you decide to configure the port speed and duplex modes manually, consider the following information:

•If you set the Ethernet port speed to auto, the switch automatically sets the duplex mode to auto.

•If you enter the no speed command, the switch automatically configures both speed and duplex to auto.

•If you configure an Ethernet port speed to a value other than auto (for example, 10, 100, or 1000 Mbps), configure the connecting port to match. Do not configure the connecting port to negotiate the speed.

•If you manually configure the Ethernet port speed to either 10 Mbps or 100 Mbps, the switch prompts you to also configure the duplex mode on the port.

Note A LAN port cannot automatically negotiate Ethernet port speed and duplex mode if the connecting port is configured to a value other than auto.

Caution Changing the Ethernet port speed and duplex mode configuration might shut down and reenable the interface during the reconfiguration.

Configuring the Ethernet Interface Speed

Note If you configure the Ethernet port speed to auto on a 10/100-Mbps or 10/100/1000-Mbps Ethernet port, both speed and duplex are autonegotiated.

To configure the port speed for a 10/100 or a 10/100/1000-Mbps Ethernet port, perform this task:

 
Command
Purpose

Step 1 

Router(config)# interface fastethernet slot/port

Selects the Ethernet port to be configured.

Step 2 

Router(config-if)# speed {10 | 100 | 1000 | {auto [10 100 [1000]]}}

Configures the speed of the Ethernet interface.

Router(config-if)# no speed

Reverts to the default configuration (speed auto).

When configuring the port speed for a 10/100/1000-Mbps Ethernet port, note the following:

•Enter the auto 10 100 keywords to restrict the negotiated speed to 10-Mbps or 100-Mbps.

•The auto 10 100 1000 keywords have the same effect as the auto keyword by itself.

This example shows how to configure the speed to 100 Mbps on the Fast Ethernet port 5/4: 

Router(config)# interface fastethernet 5/4

Router(config-if)# speed 100

Setting the Interface Duplex Mode

Note•10-Gigabit Ethernet and Gigabit Ethernet are full duplex only. You cannot change the duplex mode on 10-Gigabit Ethernet or Gigabit Ethernet ports or on a 10/100/1000-Mps port configured for Gigabit Ethernet.

•If you set the port speed to auto on a 10/100-Mbps or a 10/100/1000-Mbps Ethernet port, both speed and duplex are autonegotiated. You cannot change the duplex mode of autonegotiation ports.

To set the duplex mode of an Ethernet or Fast Ethernet port, perform this task:

 
Command
Purpose

Step 1 

Router(config)# interface fastethernet slot/port

Selects the Ethernet port to be configured.

Step 2 

Router(config-if)# duplex [auto | full | half]

Sets the duplex mode of the Ethernet port.

Router(config-if)# no duplex

Reverts to the default configuration (duplex auto).

This example shows how to set the duplex mode to full on Fast Ethernet port 5/4: 

Router(config)# interface fastethernet 5/4

Router(config-if)# duplex full

Configuring Link Negotiation on Gigabit Ethernet Ports

Note Link negotiation does not negotiate port speed.

On Gigabit Ethernet ports, link negotiation exchanges flow-control parameters, remote fault information, and duplex information. Link negotiation is enabled by default.

The ports on both ends of a link must have the same setting. The link will not come up if the ports at each end of the link are set inconsistently (link negotiation enabled on one port and disabled on the other port).

Table 8-1 shows the four possible link negotiation configurations and the resulting link status for each configuration.

Table 8-1 Link Negotiation Configuration and Possible Link Status 

Link Negotiation State
Link Status
Local Port
Remote Port
Local Port
Remote Port

Off

Off

Up

Up

On

On

Up

Up

Off

On

Up

Down

On

Off

Down

Up


To configure link negotiation on a port, perform this task:

 
Command
Purpose

Step 1 

Router(config)# interface gigabitethernet slot/port

Selects the port to be configured.

Step 2 

Router(config-if)# speed nonegotiate

Disables link negotiation.

Router(config-if)# no speed nonegotiate

Reverts to the default configuration (link negotiation enabled).

This example shows how to enable link negotiation on Gigabit Ethernet port 5/4: 

Router(config)# interface gigabitethernet 5/4 

Router(config-if)# no speed nonegotiate

Displaying the Speed and Duplex Mode Configuration

To display the speed and duplex mode configuration for a port, perform this task:

Command
Purpose

Router# show interfaces type1 slot/port

Displays the speed and duplex mode configuration.

1 type = fastethernet, gigabitethernet, or tengigabitethernet


This example shows how to display the speed and duplex mode of Fast Ethernet port 5/4: 

Router# show interfaces fastethernet 5/4

FastEthernet5/4 is up, line protocol is up

  Hardware is Cat6K 100Mb Ethernet, address is 0050.f0ac.3058 (bia 0050.f0ac.3058)

  MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,

     reliability 255/255, txload 1/255, rxload 1/255

  Encapsulation ARPA, loopback not set

  Keepalive set (10 sec)

  Full-duplex, 100Mb/s

  ARP type: ARPA, ARP Timeout 04:00:00

  Last input 00:00:33, output never, output hang never

  Last clearing of "show interface" counters never

  Queueing strategy: fifo

  Output queue 0/40, 0 drops; input queue 0/75, 0 drops

  5 minute input rate 0 bits/sec, 0 packets/sec

  5 minute output rate 0 bits/sec, 0 packets/sec

     1238 packets input, 273598 bytes, 0 no buffer

     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

     0 input packets with dribble condition detected

     1380 packets output, 514382 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 output buffer failures, 0 output buffers swapped out

Router#

Configuring Jumbo Frame Support

These sections describe jumbo frame support:

•Understanding Jumbo Frame Support

•Configuring MTU Sizes

Caution The following switching modules support a maximum ingress frame size of 8092 bytes:

· WS-X6516-GE-TX when operating at 100 Mbps
· WS-X6148-RJ-45, WS-X6148-RJ-45V and WS-X6148-RJ21, WS-X6148-RJ21V
· WS-X6248-RJ-45 and WS-X6248-TEL
· WS-X6248A-RJ-45 and WS-X6248A-TEL
· WS-X6348-RJ-45, WS-X6348-RJ45V and WS-X6348-RJ-21, WX-X6348-RJ21V

When jumbo frame support is configured, these modules drop ingress frames larger than 8092 bytes.

Note The WS-X6548-GE-TX, WS-X6548V-GE-TX, WS-X6148-GE-TX, and WS-X6148V-GE-TX do not support jumbo frames.

Understanding Jumbo Frame Support

These sections describe jumbo frame support:

•Jumbo Frame Support Overview

•Ethernet Ports

•VLAN Interfaces

Jumbo Frame Support Overview

A jumbo frame is a frame larger than the default Ethernet size. You enable jumbo frame support by configuring a larger-than-default maximum transmission unit (MTU) size on a port or VLAN interface and configuring the global LAN port MTU size.

Note•Jumbo frame support fragments routed traffic in software on the route processor (RP).

•Jumbo frame support does not fragment bridged traffic.

Bridged and Routed Traffic Size Check at Ingress 10, 10/100, and 100 Mbps Ethernet and 10-Gigabit Ethernet Ports

Jumbo frame support compares ingress traffic size with the global LAN port MTU size at ingress 10, 10/100, and 100 Mbps Ethernet and 10-Gigabit Ethernet LAN ports that have a nondefault MTU size configured. The port drops traffic that is oversized. You can configure the global LAN port MTU size (see the "Configuring the Global Egress LAN Port MTU Size" section).

Bridged and Routed Traffic Size Check at Ingress Gigabit Ethernet Ports

Gigabit Ethernet LAN ports configured with a nondefault MTU size accept frames containing packets of any size larger than 64 bytes. With a nondefault MTU size configured, Gigabit Ethernet LAN ports do not check for oversize ingress frames.

Routed Traffic Size Check on the PFC

For traffic that needs to be routed, Jumbo frame support on the PFC compares traffic sizes to the configured MTU sizes and provides Layer 3 switching for jumbo traffic between interfaces configured with MTU sizes large enough to accommodate the traffic. Between interfaces that are not configured with large enough MTU sizes, if the "do not fragment bit" is not set, the PFC sends the traffic to the RP to be fragmented and routed in software. If the "do not fragment bit" is set, the PFC drops the traffic.

Bridged and Routed Traffic Size Check at Egress 10, 10/100, and 100 Mbps Ethernet Ports

10, 10/100, and 100 Mbps Ethernet LAN ports configured with a nondefault MTU size transmit frames containing packets of any size larger than 64 bytes. With a nondefault MTU size configured, 10, 10/100, and 100 Mbps Ethernet LAN ports do not check for oversize egress frames.

Bridged and Routed Traffic Size Check at Egress Gigabit Ethernet and 10-Gigabit Ethernet Ports

Jumbo frame support compares egress traffic size with the global egress LAN port MTU size at egress Gigabit Ethernet and 10-Gigabit Ethernet LAN ports that have a nondefault MTU size configured. The port drops traffic that is oversized. You can configure the global LAN port MTU size (see the "Configuring the Global Egress LAN Port MTU Size" section).

Ethernet Ports

These sections describe configuring nondefault MTU sizes on Ethernet ports:

•Ethernet Port Overview

•Layer 3 Ethernet Ports

•Layer 2 Ethernet Ports

Ethernet Port Overview

Configuring a nondefault MTU size on a 10, 10/100, or 100 Mbps Ethernet port limits ingress packets to the global LAN port MTU size and permits egress traffic of any size larger than 64 bytes.

Configuring a nondefault MTU size on a Gigabit Ethernet port permits ingress packets of any size larger than 64 bytes and limits egress traffic to the global LAN port MTU size.

Configuring a nondefault MTU size on a 10-Gigabit Ethernet port limits ingress and egress packets to the global LAN port MTU size.

Configuring a nondefault MTU size on an Ethernet port limits routed traffic to the configured MTU size.

You can configure the MTU size on any Ethernet port.

Layer 3 Ethernet Ports

On a Layer 3 port, you can configure an MTU size on each Layer 3 Ethernet port that is different than the global LAN port MTU size.

Note Traffic through a Layer 3 Ethernet LAN port that is configured with a nondefault MTU size is also subject to the global LAN port MTU size (see the "Configuring the Global Egress LAN Port MTU Size" section).

Layer 2 Ethernet Ports

On a Layer 2 port, you can only configure an MTU size that matches the global LAN port MTU size (see the "Configuring the Global Egress LAN Port MTU Size" section).

VLAN Interfaces

You can configure a different MTU size on each Layer 3 VLAN interface. Configuring a nondefault MTU size on a VLAN interface limits traffic to the nondefault MTU size. You can configure the MTU size on VLAN interfaces to support jumbo frames.

Configuring MTU Sizes

These sections describe how to configure MTU sizes:

•Configuring MTU Sizes

•Configuring the Global Egress LAN Port MTU Size

Configuring the MTU Size

To configure the MTU size, perform this task:

 
Command
Purpose

Step 1 

Router(config)# interface {{vlan vlan_ID} | {{type1  slot/port} | {port-channel port_channel_number} slot/port}}

Selects the interface to configure.

Step 2 

Router(config-if)# mtu mtu_size

Configures the MTU size.

Router(config-if)# no mtu

Reverts to the default MTU size (1500 bytes).

Step 3 

Router(config-if)# end

Exits configuration mode.

Step 4 

Router# show running-config interface [{gigabitethernet | tengigabitethernet} slot/port]

Displays the running configuration.

1 type = fastethernet, gigabitethernet, tengigabitethernet, or ge-wan

When configuring the MTU size, note the following information:

•For VLAN interfaces and Layer 3 Ethernet ports, supported MTU values are from 64 to 9216 bytes.

•For Layer 2 Ethernet ports, you can configure only the global egress LAN port MTU size (see the "Configuring the Global Egress LAN Port MTU Size" section).

This example shows how to configure the MTU size on Gigabit Ethernet port 1/2: 

Router# configure terminal 

Router(config)# interface gigabitethernet 1/2 

Router(config-if)# mtu 9216

Router(config-if)# end

This example shows how to verify the configuration: 

Router# show interface gigabitethernet 1/2

GigabitEthernet1/2 is administratively down, line protocol is down

  Hardware is C6k 1000Mb 802.3, address is 0030.9629.9f88 (bia 0030.9629.9f88)

  MTU 9216 bytes, BW 1000000 Kbit, DLY 10 usec,

<...Output Truncated...>

Router#

Configuring the Global Egress LAN Port MTU Size

To configure the global egress LAN port MTU size, perform this task:

 
Command
Purpose

Step 1 

Router(config)# system jumbomtu mtu_size

Configures the global egress LAN port MTU size.

Router(config)# no system jumbomtu

Reverts to the default global egress LAN port MTU size (9216 bytes).

Step 2 

Router(config)# end

Exits configuration mode.

Configuring IEEE 802.3x Flow Control

Gigabit Ethernet and 10-Gigabit Ethernet ports use flow control to stop the transmission of frames to the port for a specified time; other Ethernet ports use flow control to respond to flow-control requests.

If a Gigabit Ethernet or 10-Gigabit Ethernet port receive buffer becomes full, the port can be configured to transmit an IEEE 802.3x pause frame that requests the remote port to delay sending frames for a specified time. All Ethernet ports can can be configured to respond to IEEE 802.3x pause frames from other devices.

To configure flow control on an Ethernet port, perform this task:

 
Command
Purpose

Step 1 

Router(config)# interface type1  slot/port

Selects the port to configure.

Step 2 

Router(config-if)# flowcontrol {receive | send} {desired | off | on}

Configures a port to send or respond to pause frames.

Router(config-if)# no flowcontrol {receive | send}

Reverts to the default flow control settings.

Step 3 

Router# show interfaces [type1 slot/port] flowcontrol

Displays the flow-control configuration for all ports.

1 type = fastethernet, gigabitethernet, or tengigabitethernet

When configuring flow control, note the following information:

•You cannot configure how WS-X6502-10GE 10-Gigabit Ethernet ports respond to pause frames. WS-X6502-10GE 10-Gigabit Ethernet ports are permanently configured to respond to pause frames.

•When configuring how a port responds to pause frames, note the following information:

–For a Gigabit Ethernet port, when the configuration of a remote port is unknown, you can use the receive desired keywords to configure the Gigabit Ethernet port to respond to received pause frames. (Supported only on Gigabit Ethernet ports.)

–Use the receive on keywords to configure a port to respond to received pause frames.

–Use the receive off keywords to configure a port to ignore received pause frames.

•When configuring transmission of pause frames on a port, note the following information:

–For a Gigabit Ethernet port, when the configuration of the remote ports is unknown, you can use the send desired keywords to configure the Gigabit Ethernet port to send pause frames. (Supported only on Gigabit Ethernet ports.)

–Use the send on keywords to configure a port to send pause frames.

–Use the send off keywords to configure a port not to send pause frames.

This example shows how to turn on receive flow control and how to verify the flow-control configuration: 

Router# configure terminal

Router(config)# interface gigabitethernet 1/2

Router(config-if)# flowcontrol receive on

Router(config-if)# end

Router# show interfaces flowcontrol


Interface Send         Receive

Gi1/1     Desired      OFF

Gi1/2     Desired      ON

Fa5/1     Not capable  OFF

<output truncated>

Configuring the Port Debounce Timer

The port debounce timer delays notification of a link change, which can decrease traffic loss due to network reconfiguration. You can configure the port debounce timer separately on each LAN port.

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

To configure the debounce timer on a port, perform this task:

 
Command
Purpose

Step 1 

Router(config)# interface type1  slot/port

Selects the port to configure.

Step 2 

Router(config-if)# link debounce [time debounce_time]

Configures the debounce timer.

Router(config-if)# no link debounce

Reverts to the default setting.

Step 3 

Router# show interfaces debounce

Verifies the configuration.

1 type = fastethernet, gigabitethernet, or tengigabitethernet

When configuring the debounce timer on a port, note the following information:

•The time keyword is supported only on fiber Gigabit Ethernet ports.

•You can increase the port debounce timer value in increments of 100 milliseconds up to 5000 milliseconds on ports operating at 1000 Mpbs over copper media.

•The debounce timer recognizes 10 Gbps copper media and detects media-only changes.

Table 8-2 lists the time delay that occurs before notification of a link change.

Table 8-2 Port Debounce Timer Delay Time 

Port Type
Debounce Timer Disabled
Debounce Timer Enabled

Ports operating at 10 Mpbs or 100 Mbps

300 milliseconds

3100 milliseconds

Ports operating at 1000 Mpbs or 10 Gbps over copper media

300 milliseconds

3100 milliseconds

Ports operating at 1000 Mpbs or 10 Gbps over fiber media except WS-X6502-10GE

10 milliseconds

100 milliseconds

WS-X6502-10GE 10-Gigabit ports

1000 milliseconds

3100 milliseconds


This example shows how to enable the port debounce timer on Fast Ethernet port 5/12: 

Router(config)# interface fastethernet 5/12 

Router(config-if)# link debounce 

Router(config-if)# end

This example shows how to display the port debounce timer settings: 

Router# show interfaces debounce | include enable 

Fa5/12  enable          3100

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 the following commands: show configuration, show running-config, and show interfaces.

To add a description for an interface, perform this task:

Command
Purpose

Router(config-if)# description string

Adds a description for an interface.

Router(config-if)# no description

Deletes a description from an interface.


This example shows how to add a description on Fast Ethernet port 5/5: 

Router(config)# interface fastethernet 5/5 

Router(config-if)# description Channel-group to "Marketing"

Understanding Online Insertion and Removal

The online insertion and removal (OIR) feature supported on the Catalyst 6500 series switches allows you to remove and replace modules while the system is online. You can shut down the modules before removal and restart it after insertion without causing other software or interfaces to shut down.

Note Do not remove or install more than one module at a time. After you remove or install a module, check the LEDs before continuing. For module LED descriptions, see the Catalyst 6500 Series Switch Installation Guide.

When a module has been removed or installed, the Catalyst 6500 series switch stops processing traffic for the module and scans the system for a configuration change. Each interface type is verified against the system configuration, and then the system runs diagnostics on the new module. There is no disruption to normal operation during module insertion or removal.

The switch can bring only an identical replacement module online. To support OIR of an identical module, the module configuration is not removed from the running-config file when when you remove a module.

If the replacement module is different from the removed module, you must configure it before the switch can bring it online.

Layer 2 MAC addresses are stored in an EEPROM, which allows modules to be replaced online without requiring the system to update switching tables and data structures. Regardless of the types of modules installed, the Layer 2 MAC addresses do not change unless you replace the supervisor engine. If you do replace the supervisor engine, the Layer 2 MAC addresses of all ports change to those specified in the address allocator on the new supervisor engine.

Monitoring and Maintaining Interfaces

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

•Monitoring Interface Status

•Clearing Counters on an Interface

•Resetting an Interface

•Shutting Down and Restarting an Interface

Monitoring Interface Status

The software contains commands that you can enter at the EXEC prompt to display information about the interface including the version of the software and the hardware and statistics about interfaces. The following table lists some of the interface monitoring commands. (You can display the complete list of show commands by using the show ? command at the EXEC prompt.) These commands are described in the Cisco IOS Interface Command Reference publication.

To display information about the interface, perform these tasks:

Command
Purpose

Router# show ibc

Displays current internal status information.

Router# show eobc

Displays current internal out-of-band information.

Router# show interfaces [type slot/port]

Displays the status and configuration of all or a specific interface.

Router# show running-config

Displays the currently running configuration.

Router# show rif

Displays the current contents of the routing information field (RIF) cache.

Router# show protocols [type slot/port]

Displays the global (system-wide) and interface-specific status of any configured protocol.

Router# show version

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


This example shows how to display the status of Fast Ethernet port 5/5: 

Router# show protocols fastethernet 5/5 

FastEthernet5/5 is up, line protocol is up

Router#

Clearing Counters on an Interface

To clear the interface counters shown with the show interfaces command, perform this task:

Command
Purpose

Router# clear counters {{vlan vlan_ID} | {type1  slot/port} | {port-channel channel_ID}}

Clears interface counters.

1 type = fastethernet, gigabitethernet, or tengigabitethernet


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

Router# clear counters fastethernet 5/5 

Clear "show interface" counters on this interface [confirm] y 

Router#

*Sep 30 08:42:55: %CLEAR-5-COUNTERS: Clear counter on interface FastEthernet5/5

The clear counters command clears all the current counters from the interface unless the optional arguments specify a specific interface.

Note The clear counters command clears counters displayed with the EXEC show interfaces command, not counters retrieved using SNMP.

Resetting an Interface

To reset an interface, perform this task:

Command
Purpose

Router# clear interface type1 slot/port

Resets an interface.

1 type = fastethernet, gigabitethernet, or tengigabitethernet


This example shows how to reset Fast Ethernet port 5/5: 

Router# clear interface fastethernet 5/5 

Router#

Shutting Down and Restarting an Interface

You can shut down an interface, which disables all functions on the specified interface and shows 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 included in any routing updates.

To shut down an interface and then restart it, perform this task:

 
Command
Purpose

Step 1 

Router(config)# interface {{vlan vlan_ID} | {type1  slot/port} | {port-channel channel_ID}}

Selects the interface to be configured.

Step 2 

Router(config-if)# shutdown

Shuts down the interface.

Step 3 

Router(config-if)# no shutdown

Reenables the interface.

1 type = fastethernet, gigabitethernet, or tengigabitethernet

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

Router(config)# interface fastethernet 5/5 

Router(config-if)# shutdown 

Router(config-if)#

*Sep 30 08:33:47: %LINK-5-CHANGED: Interface FastEthernet5/5, changed state to 
administratively down

This example shows how to reenable Fast Ethernet port 5/5: 

Router(config-if)# no shutdown 

Router(config-if)#

*Sep 30 08:36:00: %LINK-3-UPDOWN: Interface FastEthernet5/5, changed state to up

To check if an interface is disabled, enter the EXEC show interfaces command. An interface that has been shut down is shown as administratively down in the show interfaces command display.

Checking the Cable Status Using the TDR

You can check the status of copper cables using the time domain reflectometer (TDR). The TDR detects a cable fault by sending a signal through the cable and reading the signal that is reflected back to it. All or part of the signal can be reflected back by any number of cable defects or by the end of the cable itself.

Use the TDR to determine if the cabling is at fault if you cannot establish a link. This test is especially important when replacing an existing switch, upgrading to Gigabit Ethernet, or installing new cables.

The port must be up before running the TDR test. If the port is down, you cannot enter the test cable-diagnostics tdr command successfully, and the following message is displayed: 

Router# test cable-diagnostics tdr interface gigabitethernet2/12 

% Interface Gi2/12 is administratively down

% Use 'no shutdown' to enable interface before TDR test start.

Note•TDR can test cables up to a maximum length of 115 meters.

•See the Release Notes for Cisco IOS Release 12.2(33)SXH and Later Releases for information about which modules support the TDR.

To start or stop the TDR test, perform this task:

Command
Purpose

test cable-diagnostics tdr interface {interface interface_number}

Starts or stops the TDR test.


This example shows how to run the TDR-cable diagnostics: 

Router # test cable-diagnostics tdr interface gigabitethernet2/1 

TDR test started on interface Gi2/1 

A TDR test can take a few seconds to run on an interface 

Use 'show cable-diagnostics tdr' to read the TDR results.

Router #