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Using Loopback Testing for ATM Interfaces

 

Checklist for Using Loopback Testing for ATM Interfaces

Purpose

To use loopback testing for ATM interfaces.

Action

Table 1 provides links and commands for using loopback testing for ATM interfaces.

Table 1: Checklist for Using Loopback Testing for ATM Interfaces

Tasks

Command or Action

Diagnosing a Suspected Hardware Problem with an ATM1 or ATM2 IQ Interface
  1. Creating a Loopback

 

Connect the transmit port to the receive port.

[edit interfaces interface-name (sonet-options | t3-options)]

set loopback local

show

commit

  1. Setting Clocking to Internal

[edit interfaces interface-name]

set clocking internal

show

commit

  1. Verifying That the ATM Interface Is Up

show interfaces at-fpc/port/pic

  1. Clearing ATM Interface Statistics

clear interfaces statistics at-fpc/port/pic

  1. Pinging the ATM Interface

ping interface at-fpc/port/pic local-IP-address bypass-routing count 1000 rapid

  1. Checking for ATM Interface Error Statistics

show interfaces at-fpc/port/pic extensive

Diagnosing a Suspected Circuit Problem
  1. Creating a Loop from the Router to the Network

[edit interfaces interface-name (sonet-options | t3-options)]

set loopback remote

show

commit

  1. Creating a Loop to the Router from Various Points in the Network

Perform Steps 2 through 6 from Diagnosing a Suspected Hardware Problem with an ATM1 or ATM2 IQ Interface.

Diagnosing a Suspected Hardware Problem with an ATM1 or ATM2 IQ Interface

Problem

Description: When you suspect a hardware problem, perform the following steps to verify if there is a hardware problem.

Solution

To diagnose a suspected hardware problem with an ATM1 or ATM2 IQ interface, follow these steps:

  1. Creating a Loopback

  2. Setting Clocking to Internal

  3. Verifying That the ATM Interface Is Up

  4. Clearing ATM Interface Statistics

  5. Pinging the ATM Interface

  6. Checking for ATM Interface Error Statistics

Creating 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).





Creating a Physical Loopback

Create a physical loopback from the transmit port to the receive port.

Note

Make sure you use single-mode fiber for a single-mode port and multimode fiber for a multimode port for SONET media.

  1. To create a physical loopback at the port, connect the transmit port to the receive port using a known good cable.

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.



Configuring a Local Loopback

Purpose

Because ATM interfaces can be either SONET or T3, you use the sonet-options or t3-options statements to configure a local loopback. Figure 1 illustrates a local loopback configured for an ATM interface.

Figure 1: Local Loopback
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.

Setting Clocking to Internal

Purpose

Clocking is set 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 the 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.

Verifying That the ATM Interface Is Up

Purpose

Displaying the status of the ATM interface provides the information you need to determine whether the physical link is up or down.

Action

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

Sample Output 1

The following sample output is for an OC3 ATM interface:

Sample Output 2

The following sample output is for a T3 ATM interface:

Sample Output 3

The following sample output is for an OC3 ATM interface:

Sample Output 4

The following sample output is for a T3 ATM interface:

Meaning

Sample output 1 shows that the physical link is up and there are no SONET alarms or defects.

Sample output 2 shows that the physical link is up and there are no active alarms or defects.

Sample output 3 shows that the physical link, the device flags, and interface flags are down, and that there are SONET alarms and defects. When you see that the physical link is down, there may be a problem with the port.

Sample output 4 shows that the physical link, the device flags, and interface flags are down, and that there are active alarms and defects. When you see that the physical link is down, there may be a problem with the port.

For more information about problem situations and actions to take for a physical link that is down, see Table 2.

Table 2: Problems and Solutions for a Physical Link That Is Down

Problem

Actions

Cable mismatch

Verify that the cable connection is correct.

Damaged fiber or coax cable or dirty fiber cable

Verify that the cable can successfully loop a known good port of the same type.

Too much or too little optical attenuation (for an OC3 or OC12 ATM interface)

Verify that the attenuation is correct per the PIC optical specification.

The transmit port is not transmitting within the dBm optical range per the specifications (for an OC3 or OC12 ATM interface)

Verify that the Tx power of the optics is within range of the PIC optical specification.

Clearing ATM Interface Statistics

Purpose

You must reset ATM interface statistics before you initiate the ping test. Resetting the statistics provides a clean start so that previous input or output errors and packet statistics do not interfere with the current investigation.

Action

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

Sample Output

Meaning

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

Pinging the ATM Interface

Purpose

After you have put the port in a local loopback, run the ping test using the following Junos OS CLI operational mode command:

Action

Sample Output

user@host> ping interface at-2/0/0.0 192.168.1.1 bypass-routing count 1000 rapid

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).

Checking for ATM 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

The following sample output is for an OC3 ATM interface:

Sample Output

The following sample output is for a T3 ATM interface:

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 the 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).

Diagnosing a Suspected Circuit Problem

When you suspect a circuit problem, it is important to work with the transport-layer engineer to resolve the problem. The transport-layer engineer may ask you to create a loop from the router to the network, or the engineer may create a loop to the router from various points in the network.

To diagnose a suspected circuit problem, follow these steps:

  1. Creating a Loop from the Router to the Network

  2. Creating a Loop to the Router from Various Points in the Network



Creating a Loop from the Router to the Network

Purpose

Creating a loop from the router to the network allows the transport-layer engineer to test the router from various points in the network. This helps the engineer isolate where the problem might be located. Figure 2 illustrates a loop from a router to the network.

Figure 2: Loop from the Router to the Network
Loop from the Router to the Network

Action

To create a loop from the router to the network, follow these steps:

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

  2. Configure the remote loopback:

  3. Verify the configuration:

    For example:

  4. Commit the change:

    For example:



Creating a Loop to the Router from Various Points in the Network

Purpose

The transport-layer engineer creates a loop to the router from various points in the network. You can then perform tests to verify the connection from the router to that loopback in the network.

Action

After the transport-layer engineer has created the loop to the router from the network, you must verify the connection from the router to the loopback in the network. Follow Steps 2 through 6 in Diagnosing a Suspected Hardware Problem with an ATM1 or ATM2 IQ Interface. Keep in mind that any problems encountered in the test indicate a problem with the connection from the router to the loopback in the network.

By performing tests to loopbacks at various points in the network, you can isolate the source of the problem.