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Diagnose a Suspected Hardware Problem with a T3 Interface

 

When you suspect a hardware problem, take the following steps to help verify if there is a hardware problem.

To diagnose a suspected hardware problem with a T3 interface, follow these steps:

Create a Loopback

You can create a physical loopback or configure a local loopback to help diagnose a suspected hardware problem. Creating a physical loopback is recommended because it allows you to test and verify the transmit and receive ports. If a field engineer is not available to create the physical loopback, you can configure a local loopback for the interface. The local loopback creates a loopback internally in the Physical Interface Card (PIC).



Create a Physical Loopback

Action

To create a physical loopback at the port, connect the transmit port to the receive port.

Meaning

When you create and test a physical loopback, you are testing the transmit and receive ports of the PIC. This action is recommended if a field engineer is available to create the physical loop as it provides a more complete test of the PIC.



Configure a Local Loopback

Action

To configure a local loopback without physically connecting the transmit port to the receive port, follow these steps:

  1. In configuration mode, go to the following hierarchy level:

  2. Configure the loopback:

  3. Verify the configuration:

    For example:

  4. Commit the change:

    For example:

Meaning

When you create a local loopback, you create an internal loop on the interface being tested. A local loopback loops the traffic internally on that PIC. A local loopback tests the interconnection of the PIC but does not test the transmit and receive ports.

Note

Remember to delete the loopback statement after completing the test.

Set Clocking to Internal

Purpose

You set clocking to internal because there is no external clock source in a loopback connection.

Action

To configure clocking to internal, follow these steps:

  1. In configuration mode, go to the following hierarchy level:

  2. Configure clocking to internal:

  3. Verify the configuration:

    For example:

  4. Commit the change:

    For example:

Meaning

The clock source for the interface is set to the internal Stratum 3 clock.

Verify That the T3 Interface Is Up

Purpose

Display the status of the T3 interface to provide the information you need to determine whether the physical link is up or down.

Action

To verify that the status of the T3 interface is up, use the following Junos OS CLI operational mode command:

Sample Output

The following output is for a T3 interface with the physical link up:

Meaning

The sample output shows that the physical link is up, the loop is detected, and there are no T3 alarms or defects.

Sample Output

If the physical link is down, there may be a problem with the port. The following output is an example of the show interfaces t3-fpc/pic/port command when the physical link is down:

Meaning

The sample output shows that the physical link is down, the device flags and interface flags are down, and that there are T3 alarms and defects. Verify that the fiber can successfully loop a known good port of the same type by checking for damage to the cable.

Clear T3 Interface Statistics

Purpose

You must reset T3 interface statistics before initiating the ping test. Resetting the statistics provides a clean start so that previous input/output errors and packet statistics do not interfere with the current diagnostics.

Action

To clear all statistics for the interface, use the following Junos OS CLI operational mode command:

Sample Output

user@host> clear interfaces statistics t3-4/0/2

Meaning

This command clears the interface statistics counters for interface t3-4/0/2 only.

Force the Link Layer To Stay Up

To complete the loopback test, the link layer must remain up. However, Junos OS is designed to recognize that loop connections are not valid connections and to bring the link layer down. You need to force the link layer to stay up by making some configuration changes to the encapsulation and keepalives.

To force the link layer to stay up, follow these steps:



Configure Encapsulation to Cisco-HDLC

Action

To configure encapsulation on a T3 physical interface, follow these steps:

  1. In configuration mode, go to the following hierarchy level:

  2. Configure Cisco-HDLC:

  3. Verify the configuration:

    For example:

  4. Commit the change:

    For example:

Meaning

This command sets the interface encapsulation to the Cisco High-Level Data-Link Control (HDLC) transport protocol.

Configure No-Keepalives

Action

To disable the sending of link-layer keepalives on a T3 physical interface, follow these steps:

  1. In configuration mode, go to the following hierarchy level:

  2. Configure no-keepalives:

  3. Verify the configuration:

    For example:

  4. Commit the change:

    For example:

Meaning

By setting no-keepalives, the link layer is forced to stay up. If the setting remains at keepalive, the router will recognize that the same link-layer keepalives are being looped back and will bring the link layer down.

Related Documentation

Verify the Status of the Logical Interface

Purpose

To verify the status of the logical interface, use the following two Junos OS CLI operational mode commands:

Action

Sample Output

The following sample output is for a T3 logical interface that is up:

Meaning

The sample output for the first command shows that the logical link is up because there are no flags indicating that the link layer is down. The output for the show interfaces terse command shows that logical interface t3-1/0/0 is up.

Sample Output

The following sample output is for a T3 logical interface that is down:

Meaning

The sample output for both commands shows that the logical interface is down. The first command shows that the link layer, device, and destination route are all down. The second command shows that logical interface t3-0/2/0 is down.

Ping the T3 Interface

Purpose

Use the ping command to verify the loopback connection.

Action

To ping the local interface, use the following Junos OS CLI operational mode command:

Sample Output

user@host# ping interface t3-2/2/0 10.0.2.1 bypass-routing count 1000 rapid

PING 10.0.2.1 (10.0.2.1): 56 data bytes

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Meaning

This command sends 1000 ping packets out of the interface to the local IP address. The ping should complete successfully with no packet loss. If there is any persistent packet loss, open a case with the Juniper Networks Technical Assistance Center (JTAC) at support@juniper.net, or at 1-888-314-JTAC (within the United States) or 1-408-745-9500 (from outside the United States).

Check for T3 Interface Error Statistics

Purpose

Persistent interface error statistics indicate that you need to open a case with JTAC.

Action

To check the local interface for error statistics, use the following Junos OS CLI operational mode command:

Sample Output

user@router> show interfaces t3-1/0/0 extensive

Meaning

Check for any error statistics that may appear in the output. There should not be any input or output errors. If there are any persistent input or output errors, open a case with JTAC at support@juniper.net, or at 1-888-314-JTAC (within the United States) or 1-408-745-9500 (from outside the United States).