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
- Set Clocking to Internal
- Verify That the T3 Interface Is Up
- Clear T3 Interface Statistics
- Force the Link Layer To Stay Up
- Verify the Status of the Logical Interface
- Ping the T3 Interface
- Check for T3 Interface Error Statistics
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:
- In configuration mode, go to the following hierarchy level:[edit]user@host# edit interfaces interface-name t3-options
- Configure the loopback:[edit interfaces interface-name t3-options]user@host# set loopback local
- Verify the configuration:user@host# show
For example:
[edit interfaces t3-1/0/0 t3-options]user@host# show loopback local; - 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:
- In configuration mode, go to the following hierarchy level:[edit] user@host# edit interfaces interface-name
- Configure clocking to internal:[edit interfaces interface-name] user@host# set clocking internal
- Verify the configuration:user@host# show
For example:
[edit interfaces t3-1/0/0]user@host# show clocking internal; - 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:
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.
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 user@host>
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:
- In configuration mode, go to the following hierarchy level:[edit]user@host# edit interfaces interface-name
- Configure Cisco-HDLC:[edit interfaces interface-name] user@host# set encapsulation cisco-hdlc
- Verify the configuration:user@host# show
For example:
[edit interfaces t3-1/0/0]user@host# show encapsulation hdlc; - Commit the change:user@host# commit
For example:
[edit interfaces t3-1/0/0]user@host# commit commit complete
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:
- In configuration mode, go to the following hierarchy level:[edit]user@host# edit interfaces interface-name
- Configure no-keepalives:[edit interfaces interface-name]user@host# set no-keepalives
- Verify the configuration:user@host# show
For example:
[edit interfaces t3-1/0/0]user@host# show no-keepalives; - Commit the change:user@host# commit
For example:
[edit interfaces t3-1/0/0]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 two Junos OS CLI operational mode commands:
Action
Sample Output
The following sample output is for a T3 logical interface that is up:
user@router> show interfaces t3-1/0/0
Physical interface: t3-1/0/0, Enabled, Physical link is Up
Interface index: 13, SNMP ifIndex: 12
Link-level type: Cisco-HDLC, MTU: 4474, Clocking: Internal, Speed: T3, Loopback: None, FCS: 16,
Mode: C/Bit parity
Device flags : Present Running
Interface flags: Point-To-Point SNMP-Traps
Link flags : No-Keepalives
Input rate : 0 bps (0 pps)
Output rate : 0 bps (0 pps)
Active alarms : None
Active defects : None
Logical interface t3-1/0/0.0 (Index 126) (SNMP ifIndex 13)
Flags: Point-To-Point SNMP-Traps Encapsulation: Cisco-HDLC
Protocol inet, MTU: 4470, Flags: None
Addresses, Flags: Is-Preferred Is-Primary
Destination: 1.1.1.0/30, Local: 1.1.1.1
user@router> show interfaces terse t3-1/0/0
Interface Admin Link Proto Local Remote
t3-1/0/0 up up
t3-1/0/0.0 up up inet 1.1.1.1/30
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:
user@router> show interfaces t3-0/2/0
Physical interface: t3-0/2/0, Enabled, Physical link is Up
Interface index: 13, SNMP ifIndex: 12
Link-level type: Cisco-HDLC, MTU: 4474, Clocking: Internal, Speed: T3, Loopback: None, FCS: 16,
Mode: C/Bit parity
Device flags : Present Running
Interface flags: Link-Layer-Down Point-To-Point SNMP-Traps
Link flags : Keepalives
Keepalive settings: Interval 10 seconds, Up-count 1, Down-count 3
Keepalive: Input: 0 (never), Output: 9 (00:00:04 ago)
Input rate : 0 bps (0 pps)
Output rate : 0 bps (0 pps)
Active alarms : None
Active defects : None
Logical interface t3-0/2/0.0 (Index 126) (SNMP ifIndex 13)
Flags: Device-Down Point-To-Point SNMP-Traps Encapsulation: Cisco-HDLC
Protocol inet, MTU: 4470, Flags: None
Addresses, Flags: Dest-route-down Is-Preferred Is-Primary
Destination: 1.1.1.0/30, Local: 1.1.1.1
user@router> show interfaces terse t3-0/2/0
Interface Admin Link Proto Local Remote
t3-0/2/0 up down
t3-0/2/0.0 up down inet 1.1.1.1/30
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
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!--- 10.0.2.1 ping statistics --- 1000 packets transmitted, 1000 packets received, 0% packet loss round-trip min/avg/max/stddev = 0.374/0.446/9.744/0.754 ms
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 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 statistics:
Input : 116 (last seen 00:02:59 ago)
Output: 187 (last seen 00:00:09 ago)
Statistics last cleared: Never
Traffic statistics:
Input bytes : 2552 0 bps
Output bytes : 3703 0 bps
Input packets: 116 0 pps
Output packets: 161 0 pps
Input errors :
Errors: 0, Drops: 0, Framing errors: 229, Policed discards: 1
L3 incompletes: 0, L2 channel errors: 0, L2 mismatch timeouts: 0
SRAM errors: 0, HS link CRC errors: 0
Output errors:
Carrier transitions: 4, Errors: 0, Drops: 0, Aged packets: 0
Active alarms : LOF, LOS
Active defects : LOF, LOS
DS3 Media : Seconds Count State
PLL Lock 0 0 OK
Reframing 273 2 Defect Active
AIS 0 0 OK
LOF 273 2 Defect Active
LOS 273 2 Defect Active
IDLE 0 0 OK
YELLOW 0 0 OK
BPV 0 0
EXZ 0 0
LCV 275 18022125
PCV 0 0
CCV 0 0
LES 275
PES 273
PSES 273
CES 273
CSES 273
SEFS 273
UAS 277
HDLC configuration:
Policing bucket: Disabled
Shaping bucket : Disabled
Giant threshold: 4484, Runt threshold: 3
DSU configuration:
Compatibility mode: None, Scrambling: Disabled, Subrate: Disabled
FEAC loopback: Inactive, Response: Disabled, Count: 0
BERT time period: 10 seconds, Elapsed: 0 seconds
Algorithm: 2^3 - 1, Pseudorandom (1), Error rate: 10e-0
PFE configuration:
Destination slot: 1, Stream number: 0, PLP byte: 1 (0x00)
COS transmit queue bandwidth:
Queue0: 95, Queue1: 0, Queue2: 0, Queue3: 5
COS weighted round robin:
Queue0: 95, Queue1: 0, Queue2: 0, Queue3: 5
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, Flags: None
Addresses, Flags: Dest-route-down Is-Preferred Is-Primary
Destination: 1.1.1.0/30, Local: 1.1.1.1, Broadcast: Unspecified
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).
