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Investigating Interface Steps and Commands

 

This section includes the following information to assist you when troubleshooting interfaces:

Investigating Interface Steps and Commands Overview

The Monitoring Interfaces section helps you determine the nature of the interface problem. The Performing a Loopback Test on an Interface section provides information to help you isolate the source of the problem. The Locating Interface Alarms section explains some of the alarms and errors for the media.

Monitoring Interfaces

Problem

Description: The following steps are a general outline of how you monitor interfaces to determine the nature of interface problems. For more detailed information on a specific interface, see the corresponding monitor interfaces section.

Solution

To monitor interfaces, follow these steps:

  1. Display the status of an interface.

  2. Display the status of a specific interface.

  3. Display extensive status information for a specific interface.

  4. Monitor statistics for an interface.

The Table 1 lists and describes the operational mode commands you use to monitor interfaces.

Table 1: Commands Used to Monitor Interfaces

CLI Command

Description

show interfaces terse interface-name

For example: show interfaces terse t1*

Displays summary information about the named interfaces.

show interfaces interface-name

For example: show interfaces t1-x/y/z

Displays static status information about a specific interface.

show interfaces interface-name extensive

For example: show interfaces t1-x/y/z extensive

Displays very detailed interface information about a specific interface.

monitor interface interface-name

For example: monitor interface t1-x/y/z

Displays real-time statistics about a physical interface, updated every second.

Performing a Loopback Test on an Interface

Problem

Description: The following steps are a general outline of how you use loopback testing to isolate the source of the interface problem. For more detailed information on a specific interface, see the corresponding loopback section.

Solution

To use loopback testing for interfaces, follow these steps:

  1. To diagnose a suspected hardware problem:

    1. Create a loopback.

    2. Set clocking to internal. (Not for Fast Ethernet/Gigabit Ethernet or Multichannel DS3 interfaces.)

    3. Verify that the status of the interface is up.

    4. Configure a static address resolution protocol table entry. (Fast Ethernet/Gigabit Ethernet interfaces only)

    5. Clear the interface statistics.

    6. Force the link layer to stay up.

    7. Verify the status of the logical interface.

    8. Ping the interface.

    9. Check for interface error statistics.

  1. To diagnose a suspected connection problem:

    1. Create a loop from the router to the network.

    2. Create a loop to the router from various points in the network.

The Table 2 lists and describes the operational and configuration mode commands you use to perform loopback testing on interfaces (the commands are shown in the order in which you perform them).

Table 2: Commands Used to Perform Loopback Testing on Interfaces

CLI Statement or Command

Interface Type

Description

[edit interfaces interface-name interface-options]

set loopback (local | remote)

All interfaces

The loopback statement at the hierarchy level configures a loopback on the interface. Packets can be looped on either the local router or the remote channel service unit (CSU).

To turn off loopback, remove the loopback statement from the configuration.

show

All interfaces

Verify the configuration before you commit it.

commit

All interfaces

Save the set of changes to the database and cause the changes to take operational effect.

Use after you have verified a configuration in all configuration steps.

[edit interfaces interface-name]

set clocking internal

T1, T3, ATM, and SONET interfaces

The clocking statement at this hierarchy level configures the clock source of the interface to internal.

show interfaces interface-name

Used for all interfaces

Display static status information about a specific interface.

[edit interfaces interface-name unit logical-unit-number family inet address ip-address]

set arp ip-address mac mac-address

Fast Ethernet and Gigabit Ethernet interfaces

The arp statement at this hierarchy level defines mappings between IP and Media Access Control (MAC) addresses.

show arp no-resolve

Fast Ethernet and Gigabit Ethernet interfaces

Display the entries in the ARP table without attempting to determine the hostname that corresponds to the IP address (the no-resolve option).

clear interfaces statistics interface-name

All interfaces

Reset the statistics for an interface to zero.

[edit interfaces interface-name]

set encapsulation cisco-hdlc

T1, T3, SONET, and Multichannel DS3 interfaces

The encapsulation statement at this hierarchy level sets the encapsulation to the Cisco High-level Data-Link Control (HDLC) transport protocol on the physical interface.

[edit interfaces interface-name]

set no-keepalives

T1, T3, SONET, and Multichannel DS3 interfaces

The no-keepalives statement at this level disables the sending of keepalives on the physical interface.

show interfaces interface-name terse

T1, T3, and SONET interfaces

Display summary information about interfaces. (Use to display the status of the logical interfaces for these interfaces.)

ping interface t1-x/y/z local-ip-address bypass-routing count 1000 rapid

All interfaces

Check the reachability of network hosts by sending ICMP ECHO_REQUEST messages to elicit ICMP ECHO_RESPONSE messages from the specified host.

Use the bypass-routing option to ping a local system through an interface that has no route through it.

The count option sends 1000 ping requests through the system.

Type Ctrl+C to interrupt a ping command.

show interfaces interface-name extensive

All interfaces

Display very detailed interface information about a specific interface.

Locating Interface Alarms

Problem

Description: Locating alarms and errors for the media can be a simple process.

Solution

To locate interface alarms and errors, use the show interfaces interface-name extensive command and examine the output for active alarms and defects.