Help us improve your experience.

Let us know what you think.

Do you have time for a two-minute survey?

TechLibrary
Navigation

Use Loopback Testing for T3 Interfaces

This section includes the following information to assist you when troubleshooting T3 interfaces:

Checklist for Using Loopback Testing for T3 Interfaces

Purpose

To use loopback testing to isolate T3 interface problems.

Action

Table 1 provides links and commands for using loopback testing for T3 interfaces.

Table 1: Checklist for Using Loopback Testing for T3 Interfaces

Diagnose a Suspected Hardware Problem with a T3 Interface

Command or Action

  1. Create a Loopback
 

Connect the transmit port to the receive port.

[edit interfaces interface-name t3-options]
set loopback local
show
commit

  1. Set Clocking to Internal

[edit interfaces interface-name]
set clocking internal
show
commit

  1. Verify That the T3 Interface Is Up

show interfaces t3-fpc/pic/port

  1. Clear T3 Interface Statistics

clear interfaces statistics t3-fpc/pic/port

  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 t3-fpc/pic/port
 show interfaces t3-fpc/pic/port terse

  1. Ping the T3 Interface

ping interface t3-fpc/pic/port local-IP-address bypass-routing count 1000 rapid

  1. Check for T3 Interface Error Statistics

show interfaces t3-fpc/pic/port extensive

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

[edit interfaces interface-name t3-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 T3 Interface.

Diagnose a Suspected Hardware Problem with a T3 Interface

Problem

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

Solution

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).

  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 without physically connecting the transmit port to the receive port, follow these steps:

  1. In configuration mode, go to the following hierarchy level:
    [edit]user@host# edit interfaces interface-name t3-options
  2. Configure the loopback:
    [edit interfaces interface-name t3-options]user@host# set loopback local
  3. Verify the configuration:
    user@host# show

    For example:

    [edit interfaces t3-1/0/0 t3-options]user@host# show loopback local;
  4. Commit the change:
    user@host# commit

    For example:

    [edit interfaces t3-1/0/0 t3-options]user@host# commit commit complete

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:
    [edit] user@host# edit interfaces interface-name
  2. Configure clocking to internal:
    [edit interfaces interface-name] user@host# set clocking internal
  3. Verify the configuration:
    user@host# show

    For example:

    [edit interfaces t3-1/0/0]user@host# show clocking internal;
  4. Commit the change:
    user@host# commit

    For example:

    [edit interfaces t3-1/0/0]user@host# commit commit complete

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:

user@host> show interfaces t3-fpc/pic/port

Sample Output

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

user@router>  show interfaces t3-1/0/0
Physical interface: t3-1/0/0, Enabled,  Physical link is Up
  Interface index: 9, SNMP ifIndex: 10
  Link-level type: PPP, MTU: 4474, Clocking: Internal
  Speed: T3, Loopback: None, CRC: 16, Mode: C/Bit parity
  Device flags   : Present Running  Loop-Detected
  Interface flags: Link-Layer-Down Point-To-Point SNMP-Traps
  Link flags     : Keepalives
  Keepalive Input: 6684 (00:07:51 ago), Output: 6693 (00:06:41 ago)
  NCP state: Down, LCP state: Conf-req-sent
  Input rate     : 224 bps (2 pps), Output rate: 240 bps (2 pps)
   Active alarms  : None
   Active defects : None
  Logical interface t3-1/0/0.0 (Index 13) (SNMP ifIndex 32)
    Flags: Device-down Hardware-Down Point-To-Point SNMP-Traps
    Encapsulation: PPP
    Protocol inet, MTU: 4470, Flags: Protocol-Down
      Addresses, Flags: Dest-route-down Is-Preferred Is-Primary
        Destination: 1.1.1.0/30, Local: 1.1.1.1

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:

user@router>  show interfaces t3-1/0/0
Physical interface: t3-1/0/0, Enabled,  Physical link is Down
  Interface index: 9, SNMP ifIndex: 10
  Link-level type: Cisco-HDLC, MTU: 4474, Clocking: Internal
  Speed: T3, Loopback: None, CRC: 16, Mode: C/Bit parity
   Device flags   : Present Running Down
   Interface flags: Hardware-Down Link-Layer-Down Point-To-Point SNMP-Traps
  Link flags     : Keepalives
  Keepalive Input: 116 (00:02:32 ago), Output: 185 (00:00:02 ago)
  Input rate     : 0 bps (0 pps), Output rate: 0 bps (0 pps)
   Active alarms  : LOF, LOS
   Active defects : LOF, LOS
  Logical interface t3-1/0/0.0 (Index 12) (SNMP ifIndex 32)
    Flags: Device-down Point-To-Point SNMP-Traps, Encapsulation: Cisco-HDLC
    Protocol inet, MTU: 4470
      Addresses, Flags: Dest-route-down Is-Preferred Is-Primary
        Destination: 1.1.1.0/30, Local: 1.1.1.1

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.

Published: 2012-12-11

Published: 2012-12-11

Previous Page Next Page