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Use 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

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:
    [edit]user@host# edit interfaces interface-name (t3-options | t1-options)
  2. Configure the local loopback:
    [edit interfaces interface-name (t3-options | t1-options] user@host# set loopback local

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

    [edit interfaces t1-2/1/1:0 t1-options]
  3. Verify the configuration:
    user@host# show

    For example:

    [edit interfaces t1-2/1/1:0 t1-options]user@host# show loopback local;
  4. Commit the configuration:
    user@host# commit

    For example:

    [edit interfaces t1-2/1/1:0 t1-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.

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:

user@host> show interfaces t1-fpc/pic/port:channel user@host> show interfaces t3-fpc/pic/port:channel

Sample Output

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

user@host#  show interfaces t1-2/1/0:20                          
Physical interface: t1-2/1/0:20, Enabled, Physical link is Up
  Interface index: 210, SNMP ifIndex: 173
  Link-level type: Cisco-HDLC, MTU: 1504, Clocking: Internal, Speed: T1, Loopback: Local, FCS: 16,
  Mode: C/Bit parity, Framing: ESF
  Device flags   : Present Running
  Interface flags: Point-To-Point SNMP-Traps
  Link flags     : Keepalives
  Keepalive settings: Interval 10 seconds, Up-count 1, Down-count 3
  Keepalive: Input: 39 (00:00:06 ago), Output: 0 (never)
  CoS queues     : 4 supported
  Last flapped   : 2004-05-20 21:46:27 UTC (00:14:28 ago)
  Input rate     : 16 bps (0 pps)
  Output rate    : 160 bps (0 pps)
  DS1   alarms   : None
  DS3   alarms   : None
  DS1   defects  : None
  DS3   defects  : None
  Logical interface t1-2/1/0:20.0 (Index 74) (SNMP ifIndex 213) 
    Flags: Point-To-Point SNMP-Traps Encapsulation: Cisco-HDLC
    Protocol inet, MTU: 1500
      Flags: None
      Addresses, Flags: Is-Preferred Is-Primary
        Destination: 10.10.1.1, Local: 10.10.1.2

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:

T1 interfacesclear statistics command user@host> clear interfaces statistics t1-fpc/pic/port:channel

Sample Output

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

Meaning

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

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:
    [edit]user@host# edit interfaces interface-name
  2. Configure Cisco-HDLC:
    [edit interfaces interface-name]user@host# set encapsulation cisco-hdlc
  3. Verify the configuration:
    user@host# show

    For example:

    [edit interfaces t1-0/1/1:8]user@host# show encapsulation hdlc;
  4. Commit the change:
    user@host# commit

    For example:

    [edit interfaces t1-0/1/1:8]user@host# commit commit complete
  5. Check the interface configuration
    user@host# run show interfaces t1-2/1/0:20
    Physical interface: t1-2/1/0:20, Enabled, Physical link is Up
    Interface index: 210, SNMP ifIndex: 173
    Link-level type: Cisco-HDLC, MTU: 1504, Clocking: Internal, Speed: T1,   Loopback: Local, FCS: 16,
    Mode: C/Bit parity, Framing: ESF
    Device flags   : Present Running
    Interface flags: Point-To-Point SNMP-Traps
    Link flags     : Keepalives
    Keepalive settings: Interval 10 seconds, Up-count 1, Down-count 3
    Keepalive: Input: 39 (00:00:06 ago), Output: 0 (never)
    CoS queues     : 4 supported
    Last flapped   : 2004-05-20 21:46:27 UTC (00:14:28 ago)
    Input rate     : 16 bps (0 pps)
    Output rate    : 160 bps (0 pps)
    DS1   alarms   : None
    DS3   alarms   : None
    DS1   defects  : None
    DS3   defects  : None
    Logical interface t1-2/1/0:20.0 (Index 74) (SNMP ifIndex 213)
    Flags: Point-To-Point SNMP-Traps Encapsulation: Cisco-HDLC
    Protocol inet, MTU: 1500
    Flags: None
    Addresses, Flags: Is-Preferred Is-Primary
    Destination: 10.10.1.1, Local: 10.10.1.2

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:
    [edit]user@host# edit interfaces interface-name
  2. Configure no-keepalives:
    [edit interfaces interface-name]user@host# set no-keepalives
  3. Verify the configuration:
    user@host# show

    For example:

    [edit interfaces t1-2/1/0:20]user@host# show no-keepalives;
  4. Commit the change:
    user@host# commit

    For example:

    [edit interfaces t1-2/1/0:20]user@host# commit commit complete

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

user@host> show interfaces t1-fpc/pic/port:channel

Sample Output 1

user@host# show interfaces t1-2/1/0:20
Physical interface: t1-2/1/0:20, Enabled, Physical link is Up
  Interface index: 210, SNMP ifIndex: 173
  Link-level type: Cisco-HDLC, MTU: 1504, Clocking: Internal, Speed: T1, Loopback: Local, FCS: 16,
  Mode: C/Bit parity, Framing: ESF
  Device flags   : Present Running
  Interface flags: Point-To-Point SNMP-Traps
  Link flags     : Keepalives
  Keepalive settings: Interval 10 seconds, Up-count 1, Down-count 3
  Keepalive: Input: 39 (00:00:06 ago), Output: 0 (never)
  CoS queues     : 4 supported
  Last flapped   : 2004-05-20 21:46:27 UTC (00:14:28 ago)
  Input rate     : 16 bps (0 pps)
  Output rate    : 160 bps (0 pps)
  DS1   alarms   : None
  DS3   alarms   : None
  DS1   defects  : None
  DS3   defects  : None
  Logical interface t1-2/1/0:20.0 (Index 74) (SNMP ifIndex 213) 
    Flags: Point-To-Point SNMP-Traps Encapsulation: Cisco-HDLC
    Protocol inet, MTU: 1500
      Flags: None
      Addresses, Flags: Is-Preferred Is-Primary
        Destination: 10.10.1.1, Local: 10.10.1.2

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:

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

Sample Output

user@host> ping interface t1-2/1/0:20 10.10.1.2 bypass-routing count 1000 rapid
PING 10.10.1.2 (10.10.1.2): 56 data bytes
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! --- 10.10.1.2 ping statistics --- 1000 packets transmitted, 1000 packets received, 0% packet loss round-trip min/avg/max/stddev = 2.830/3.872/9.965/0.633 ms

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:

user@host> show interfaces t1-fpc/pic/port:channel extensive

Sample Output

user@host# show interfaces t1-2/1/0:20 extensive
Physical interface: t1-2/1/0:20, Enabled, Physical link is Up
  Interface index: 210, SNMP ifIndex: 173, Generation: 93
  Link-level type: Cisco-HDLC, MTU: 1504, Clocking: Internal, Speed: T1, Loopback: Local, FCS: 16,
  Mode: C/Bit parity, Framing: ESF
  Device flags   : Present Running
  Interface flags: Point-To-Point SNMP-Traps
  Link flags     : No-Keepalives
  Hold-times     : Up 0 ms, Down 0 ms
  CoS queues     : 4 supported
  Last flapped   : 2004-05-20 21:46:27 UTC (00:26:47 ago)
  Statistics last cleared: 2004-05-20 22:12:03 UTC (00:01:11 ago)
  Traffic statistics:
   Input  bytes  :                88680                27640 bps
   Output bytes  :                88680                27640 bps
   Input  packets:                 1010                   39 pps
   Output packets:                 1010                   39 pps
   Input errors:
    Errors: 0, Drops: 0, Framing errors: 0, Policed discards: 0, L3 incompletes: 0, L2 channel errors: 0,
    L2 mismatch timeouts: 0, HS link CRC errors: 0, SRAM errors: 0
   Output errors:
    Carrier transitions: 0, Errors: 0, Drops: 0, Aged packets: 0
  DS1   alarms   : None
  DS3   alarms   : None
  DS1   defects  : None
  DS3   defects  : None
  T1  media:            Seconds        Count  State
    SEF                       0            0  OK
    BEE                       0            0  OK
    AIS                       0            0  OK
    LOF                       0            0  OK
    LOS                       0            0  OK
    YELLOW                    0            0  OK
    BPV                       0            0
    EXZ                       0            0
    LCV                       0            0
    PCV                       0            0
    CS                        0            0
    LES                       0
    ES                        0
    SES                       0
    SEFS                      0
    BES                       0
    UAS                       0
  DS3 media:            Seconds        Count  State
    PLL Lock                  0            0  OK
    Reframing                 0            0  OK
    AIS                       0            0  OK
    LOF                       0            0  OK
    LOS                       0            0  OK
    IDLE                      0            0  OK
    YELLOW                    0            0  OK
    BPV                       0            0
    EXZ                       0            0
    LCV                       0            0
    PCV                       0            0
    CCV                       0            0
    LES                       0
    PES                       0
    PSES                      0
    CES                       0
    CSES                      0
    SEFS                      0
    UAS                       0
  Interface transmit queues:
              B/W  WRR       Packets        Bytes        Drops       Errors
    Queue0     95   95             0            0            0            0
    Queue1      5    5          1010        88680            0            0
  HDLC configuration:
    Giant threshold: 1514, Runt threshold: 3
    Timeslots      : All active
    Line encoding: B8ZS, Byte encoding: Nx64K, Data inversion: Disabled, Idle cycle flag: flags,
    Start end flag: shared
  DS-3 BERT configuration:
    BERT time period: 10 seconds, Elapsed: 0 seconds
    Algorithm: 2^3 - 1, Pseudorandom (1), Induced error rate: 10e-0
  DS1 BERT configuration:
    BERT time period: 10 seconds, Elapsed: 0 seconds
    Induced Error rate: 10e-0, Algorithm: 2^15 - 1, O.151, Pseudorandom (9)
  Packet Forwarding Engine configuration:
    Destination slot: 2, PLP byte: 2 (0x14)
    CoS transmit queue             Bandwidth           Buffer Priority   Limit
                              %          bps   %        bytes
    0 best-effort            95      1459200  95            0      low    none
    3 network-control         5        76800   5            0      low    none
  Logical interface t1-2/1/0:20.0 (Index 74) (SNMP ifIndex 213) (Generation 14)
    Flags: Point-To-Point SNMP-Traps Encapsulation: Cisco-HDLC
    Protocol inet, MTU: 1500, Generation: 24, Route table: 0
      Flags: None
      Addresses, Flags: Is-Preferred Is-Primary
        Destination: 10.10.1.1, Local: 10.10.1.2, Broadcast: Unspecified, Generation: 24

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:
    [edit]user@host# edit interfaces t1-fpc/pic/port:channel t1-options
  2. Configure the loopback:
    [edit interfaces interface-name t1-options]user@host# set loopback remote
  3. Verify the configuration:
    user@host# show

    For example:

    [edit interfaces t1-2/1/1:0:0 t1-options]user@host# show loopback remote;
  4. Commit the configuration:
    user@host# commit

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.

Published: 2012-02-28