Using Loopback Testing for SONET Interfaces
This section includes the following information to assist you when troubleshooting SONET interfaces:
Checklist for Using Loopback Testing for SONET Interfaces
Purpose
To use loopback testing to isolate SONET interface problems.
Action
Table 1 provides the links and commands for using loopback testing for SONET interfaces.
Table 1: Checklist for Using Loopback Testing for SONET Interfaces
Tasks | Command or Action |
---|---|
Diagnosing a Suspected Hardware Problem with a SONET Interface | |
Create a loopback. | |
Connect the transmit port to the receive port. | |
[edit interfaces interface-namesonet-options] | |
[edit interfaces interface-name] | |
show interfaces so-fpc/pic/port | |
clear interfaces statistics so-fpc/pic/port | |
show interfaces so-fpc/pic/port extensive | |
[edit interfaces interface-name] | |
[edit interfaces
interface-name] | |
show interfaces so-fpc/pic/port show interfaces so-fpc/pic/port terse | |
ping interface so-fpc/pic/port local-IP-address bypass-routing count 1000 rapid | |
show interfaces so-fpc/pic/port extensive | |
Diagnosing a Suspected Circuit Problem | |
[edit interfaces interface-name sonet-options] | |
Perform Steps 2 through 8 from Diagnosing a Suspected Hardware Problem with a SONET Interface. |
Diagnosing a Suspected Hardware Problem with a SONET Interface
Problem
Description: When you suspect a hardware problem, take the following steps to verify if there is a problem.
Solution
To diagnose a suspected hardware problem with the SONET interface, follow these steps:
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
Action
To create a physical loopback at the port, connect the transmit port to the receive port using a known good fiber cable.
Make sure you use a single-mode fiber for a single-mode port and multimode fiber for a multimode port. (For OC192, you must use the appropriate attentuation.)
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.
See also
Configuring 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 sonet-optionsConfigure the local loopback option.
[edit interfaces interface-name sonet-options]user@host# set loopback localVerify the configuration.
[edit interfaces interface-name sonet-options]user@host# showloopback local;Commit the change.
user@host# commit
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.
Remember to delete the loopback statement after completing the test.
See also
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:
In configuration mode, go to the following hierarchy level.
[edit]user@host# edit interfaces interface-nameConfigure clocking to internal.
[edit interfaces interface-name]user@host# set clocking internalVerify the configuration.
[edit interfaces interface-name]user@host# showclocking internal;Commit the change.
user@host# commit
Meaning
The clock source for the interface is set to the internal Stratum 3 clock.
Verifying That the SONET Interface Is Up
Purpose
Displaying the status of the SONET interface provides the information you need to determine whether the physical link is up or down.
Action
To verify that the SONET interface is up, use the following Junos OS command-line interface (CLI) operational mode command:
Sample Output 1
The following output is for a SONET interface with the physical link up:
user@host# show interfaces so-2/2/0 Physical interface: so-2/2/0, Enabled,Physical link is Up Interface index: 21, SNMP ifIndex: 45 Link-level type: PPP, MTU: 4474, Clocking: Internal, SONET mode, Speed: OC3, Loopback: None, FCS: 16, Payload scrambler: Enabled Device flags : Present Running Loop-Detected Interface flags: Point-To-Point SNMP-Traps Link flags : Keepalives Keepalive settings: Interval 10 seconds, Up-count 1, Down-count 3 Keepalive: Input: 0 (never), Output: 0 (never) LCP state: Conf-req-sent NCP state: inet: Down, inet6: Not-configured, iso: Not-configured, mpls: Not-configured Input rate : 48 bps (0 pps) Output rate : 56 bps (0 pps) SONET alarms : None SONET defects : None Logical interface so-2/2/0.0 (Index 7) (SNMP ifIndex 33) Flags: 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: 10.0.2/24, Local: 10.0.2.1
Sample Output 2
When you see that the physical link is down, there might be a problem with the port. Sample output 2 shows that the physical link is down:
user@host# show interfaces so-2/2/0 Physical interface: so-2/2/0, Enabled, Physical link is Down Interface index: 21, SNMP ifIndex: 45 Link-level type: PPP, MTU: 4474, Clocking: Internal, SONET mode, Speed: OC3, Loopback: None, FCS: 16, Payload scrambler: Enabled Device flags : Present Running Down Interface flags: Hardware-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: 0 (never) LCP state: Conf-req-sent NCP state: inet: Down, inet6: Not-configured, iso: Not-configured, mpls: Not-configured Input rate : 0 bps (0 pps) Output rate : 0 bps (0 pps) SONET alarms : LOL, LOS SONET defects : LOL, LOF, LOS, SEF, AIS-L, AIS-P Logical interface so-2/2/0.0 (Index 7) (SNMP ifIndex 33) Flags: Hardware-Down Device-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: 10.0.2/24, Local: 10.0.2.1
Meaning
Sample output 1 shows that the physical link is up, the loop is detected, and there are no SONET alarms or defects.
If the physical link is up, continue with Checking That the Received and Transmitted Path Trace Are the Same.
The sample output 2 shows that the physical link is down, the device flags and interface flags are down, and there are SONET alarms and defects.
Table 2 lists problem situations and actions for a physical link that is down.
Table 2: Problems and Solutions for a Physical Link That Is Down
Problem | Action |
---|---|
Cable mismatch | Verify that the fiber connection is correct. |
Damaged and/or dirty cable | Verify that the fiber can successfully loop a known good port of the same type. |
Too much or too little optical attenuation | Verify that the attenuation is correct per the PIC optical specifications. |
The transmit port is not transmitting within the dBm optical range per the specifications | Verify that the Tx power of the optics is within range of the PIC optical specification. |
Clearing SONET Interface Statistics
Purpose
You must reset SONET interface statistics before you initiate 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:
user@host> clear interfaces statistics so-fpc/pic/port
Sample Output
Meaning
This command clears the interface statistics counters for interface so-4/0/2 only.
See also
Checking That the Received and Transmitted Path Trace Are the Same
Purpose
The received and transmitted path trace shows whether the transmitted path trace is looped back.
Action
To check that the received path trace matches the transmitted path trace, use the following Junos OS CLI operational mode command:
Sample Output
user@host# show interfaces so-2/2/0 extensive
Physical interface: so-2/2/0, Enabled, Physical link is Up Interface index: 21, SNMP ifIndex: 45, Generation: 20 [...Output truncated...] Received path trace: host so-2/2/0 70 6c 75 74 6f 6e 69 63 20 73 6f 2d 32 2f 32 2f host so-2/2/ 30 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0 ............... 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0d 0a ................ Transmitted path trace: host so-2/2/0 70 6c 75 74 6f 6e 69 63 20 73 6f 2d 32 2f 32 2f host so-2/2/ 30 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0 ............... 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ [...Output truncated...]
Meaning
This transmitted and received path trace information is near the end of the output. The sample output shows that the transmitted and received path trace are the same. When there is a loopback, the transmitted and received path trace should be the same. If they are, continue with Forcing the Link Layer to Stay Up.
If the transmitted and received path trace are not the same, the physical loopback cable is probably on the wrong port, or is incorrectly connected. In this case, verify the connection again.
Forcing 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:
Configuring Encapsulation to Cisco-HDLC
Action
To configure encapsulation on a SONET physical interface, follow these steps:
In configuration mode, go to the following hierarchy level.
[edit]user@host# edit interfaces interface-nameConfigure Cisco-HDLC encapsulation on the interface.
[edit interfaces interface-name]user@host# set encapsulation cisco-hdlcVerify the configuration.
[edit interfaces interface-name]user@host# showencapsulation hdlc;Commit the change.
user@host# commit
Meaning
This command sets the interface encapsulation to the Cisco High-level Data-Link Control (HDLC) transport protocol.
See also
Configuring No-Keepalives
Action
To disable the sending of link-layer keepalives on a SONET physical interface, follow these steps:
In configuration mode, go to the following hierarchy level.
[edit]user@host# edit interfaces interface-nameConfigure the no-keepalives statement.
[edit interfaces interface-name]user@host# set no-keepalivesVerify the configuration.
[edit interfaces interface-name]user@host# showno-keepalives;Commit the change.
user@host# commit
Meaning
By setting the no-keepalives statement, 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.
See also
Pinging the SONET Interface
Purpose
To ping the local interface and verify the loopback connection, use the following Junos OS CLI operational mode command:
Action
Sample Output
user@host# ping interface so-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).
Checking for SONET 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 so-2/2/0 extensive
Physical interface: so-2/2/0, Enabled, Physical link is Up [...Output truncated...] Statistics last cleared: 2002-04-24 10:39:40 EDT (00:13:26 ago) Traffic statistics: Input bytes : 169686 0 bps Output bytes : 179802 0 bps Input packets: 2101 0 pps Output packets: 2102 0 pps Input errors: Errors: 0, Drops: 0, Framing errors: 0, Runts: 0, Giants: 0, Bucket drops: 0, Policed discards: 0, L3 incompletes: 0, L2 channel errors: 0, L2 mismatch timeouts: 0, HS link CRC errors: 0,HS link FIFO overflows: 0 Output errors: Carrier transitions: 0, Errors: 0, Drops: 0, Aged packets: 0, HS link FIFO underflows: 0 SONET alarms : None SONET defects : None SONET PHY: Seconds Count State PLL Lock 0 0 OK PHY Light 0 0 OK SONET section: BIP-B1 0 0 SEF 0 0 OK LOS 0 0 OK LOF 0 0 OK ES-S 0 SES-S 0 SEFS-S 0 SONET line: BIP-B2 0 0 REI-L 0 0 RDI-L 0 0 OK AIS-L 0 0 OK BERR-SF 0 0 OK BERR-SD 0 0 OK ES-L 0 SES-L 0 UAS-L 0 ES-LFE 0 SES-LFE 0 UAS-LFE 0 SONET path: BIP-B3 0 0 REI-P 0 0 LOP-P 0 0 OK AIS-P 0 0 OK RDI-P 0 0 OK UNEQ-P 0 0 OK PLM-P 0 0 OK ES-P 0 SES-P 0 UAS-P 0 ES-PFE 0 SES-PFE 0 UAS-PFE 0 [...Output truncated...]
Meaning
Check for any error statistics that may appear in the section, line, and path areas of 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).
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:
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.
Action
To create a loop from the router to the network, follow these steps:
In configuration mode, go to the following hierarchy level.
[edit]user@host# edit interfaces interface-name sonet-optionsConfigure the remote loopback option.
[edit interfaces interface-name sonet-options]user@host# set loopback remoteVerify the configuration.
[edit interfaces interface-name sonet-options]user@host# showloopback remote;Commit the change.
user@host# commit
Meaning
This command loops any traffic from the network back into the network.
See also
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 8 in Diagnosing a Suspected Hardware Problem with a SONET 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.