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Using Loopback Testing For Channelized DS3 Interfaces

 

Checklist for Using Loopback Testing for Channelized DS3 Interfaces

Purpose

To use loopback testing to isolate Channelized DS3 interface problems.

Action

Table 1 provides the links and commands for using loopback testing for Channelized DS3 interfaces.

Table 1: Checklist for Using Loopback Testing for Channelized DS3 Interfaces

Tasks

Command or Action

Diagnose a Suspected Hardware Problem with a Channelized DS3 Interface
  1. Create a Loopback

 

Connect the TX port to the RX port.

[edit interfaces interface name (t3-options | t1-options)]

set loopback local

show

commit

  1. Verify That the Interface Is Up

show interfaces t1-fpc/pic/port:channel

show interfaces t3-fpc/pic/port:channel

  1. Clear Interface Statistics

clear interfaces statistics t1-fpc/pic/port:channel

  1. Force the Link Layer to Stay Up

 

[edit interfaces interface-name]

set encapsulation cisco-hdlc

show

commit

[edit interfaces interface-name]

set no-keepalives

show

commit

  1. Verify the Status of the Logical Interface

show interfaces t1-fpc/pic/port:channel

  1. Ping the Channelized Interface

ping interface t1-fpc/pic/port:channel local-IP-address bypass-routing count 1000 rapid

  1. Check for Interface Error Statistics

show interfaces t1-fpc/pic/port:channel extensive

Diagnose a Suspected Circuit Problem
  1.  Create a Loop from the Router to the Network

[edit interfaces t1-fpc/pic/port:channel t1-options]

set loopback remote

show

commit

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

Perform Steps 2 through 8 from Diagnose a Suspected Hardware Problem with a Channelized DS3 Interface.

Diagnose a Suspected Hardware Problem with a Channelized DS3 Interface

Problem

Description: To diagnose a suspected hardware problem with a Channelized DS3 interface, follow these steps:

Solution

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 Channelized DS3 port. 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).

  1. Create a Physical Loopback

  2. Configure a Local Loopback



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, follow these steps:

  1. In configuration mode, go to the following hierarchy level, depending on whether you are configuring a full T3 or T1 interface:

  2. Configure the local loopback:

    The following is an example of the name for a T1 channel on a Channelized DS3 port for a Channelized DS3 to DS1 interface:

  3. Verify the configuration:

    For example:

  4. Commit the configuration:

    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.

Verify That the Interface Is Up

Purpose

Display the status of a Channelized DS1 or DS3 interface to determine whether the physical link is up or down.

Action

To verify that the status of the Channelized DS1 or DS3 interface is up, use one of the following Junos OS command-line interface (CLI) operational mode commands:

Sample Output

The following sample output is for a channelized DS3 to DS1 interface:

Meaning

The sample output shows that the physical link is up and there are no DS1 or DS3 alarms or defects. You should not see any DS1 or DS3 alarms. You can check any interface on the Channelized DS3 port. See “Checklist for Channelized DS3 Alarms and Errors” for more information on Channelized DS3 alarms and errors.

Clear Interface Statistics

Purpose

You must reset the Channelized DS3 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 efforts to diagnose the problem.

Action

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

Sample Output

user@host> clear interfaces statistics t1-2/1/0:20

Meaning

This command clears the interface statistics counters for the Channelized or T1 interface only.

Note

After a Graceful Routing Engine switchover (GRES) you must run clear interface statistics again or interface statistics will display junk vales.

Force the Link Layer to Stay Up

Purpose

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. If you have the Point-to-Point protocol (PPP) configured, you need to change the encapsulation to Cisco High-Level Data Link Control (HDLC) and reconfigure the keepalives in order to force the link layer to stay up.

Force the link layer to stay up, follow these steps:

  1. Configure Encapsulation to Cisco-HDLC

  2. Configure No-Keepalives



Configure Encapsulation to Cisco-HDLC

Action

To set the encapsulation on a T1 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:

  5. Check the interface configuration

    user@host# run show interfaces t1-2/1/0:20

Meaning

This command sets the interface encapsulation to the Cisco HDLC transport protocol. You must configure the interface with Cisco HDLC to ensure that the logical interface remains up in preparation for the ping test.



Configure No-Keepalives

Action

To disable the sending of link-layer keepalives on a channelized DS3 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.

Verify the Status of the Logical Interface

Purpose

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

Action

Sample Output 1

user@host# show interfaces t1-2/1/0:20

Meaning

The sample output shows that the channelized interface has the physical and logical links up.

Ping the Channelized 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 commands:

Sample Output

user@host> ping interface t1-2/1/0:20 10.10.1.2 bypass-routing count 1000 rapid

Meaning

This command sends 1000 ping packets out of the channelized interface under the Channelized DS3 port 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 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@host# show interfaces t1-2/1/0:20 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).

Diagnose a Suspected Circuit Problem

Purpose

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. Create a Loop from the Router to the Network

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



Create a Loop from the Router to the Network

Purpose

Creating a loop from a particular T1 interface to the network allows the transport-layer engineer to test the T1 interface from various points in the network and isolate the problem.

Action

To create a loop from a particular T1 interface to the network, 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 configuration:

Meaning

This command loops any traffic from the network back into the network.



Create 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 7 in Diagnose a Suspected Hardware Problem with a Channelized DS3 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.