If Layer 2 does not appear to be stable, see "Troubleshooting E1 Error Events," earlier in this chapter. If not use the encapsulation ppp command to set encapsulation. Contents Introduction. Troubleshooting Using the show interfaces serial Command. Serial Lines: show interfaces serial Status Line Conditions. Detailed Information on the show interfaces serial Command. Troubleshooting Using the show controller t1 Command. Troubleshooting Using the show controller e1 Command.
Serial x is up, line protocol is up. This is the proper status line condition. No action required. Serial x is down, line protocol is down DTE mode. Typically indicates that the router is not sensing a CD signal that is, CD is not active. Verify that you are using the proper cable and interface see your hardware installation documentation. Insert a breakout box and check all control leads. Contact your leased-line or other carrier service to see if there is a problem.
Swap faulty parts. If you suspect faulty router hardware, change the serial line to another port. If the connection comes up, the previously connected interface has a problem. Serial x is up, line protocol is down DTE mode. Put the modem, CSU, or DSU in local loopback mode and use the show interfaces serial command to see if the line protocol comes up.
If the line protocol comes up, a telephone company problem or a failed remote router is the likely problem.
Verify all cabling. Use the show controllers EXEC command to determine which cable is attached to which interface. Enable the debug serial interface EXEC command. If the line protocol does not come up in local loopback mode and if the output of the debug serial interface EXEC command shows that the keepalive counter is not incrementing, a router hardware problem is likely. Swap router interface hardware. If the line protocol comes up and the keepalive counter increments, the problem is not in the local router.
If you suspect faulty router hardware, change the serial line to an unused port. Serial x is up, line protocol is down DCE mode. Add the clockrate interface configuration command on the serial interface. Syntax: clock rate bps Syntax Description: bps -Desired clock rate in bits per second: , , , , , , , , , , , , , , , , , , or See the section "Inverting the Transmit Clock," later in this chapter. Verify that the correct cable is being used.
If the line protocol is still down, there is a possible hardware failure or cabling problem. Insert a breakout box and observe leads.
Replace faulty parts as necessary. Serial x is up, line protocol is up looped. A loop exists in the circuit. The sequence number in the keepalive packet changes to a random number when a loop is initially detected. If the same random number is returned over the link, a loop exists. Use the show running-config privileged EXEC command to look for any loopback interface configuration command entries. If you find a loopback interface configuration command entry, use the no loopback interface configuration command to remove the loop.
If they are, disable manual loopback. If the line protocol comes up, no other action is needed. If the CSU or DSU is not configured in manual loopback mode, contact the leased-line or other carrier service for line troubleshooting assistance. Serial x is up, line protocol is down disabled. Troubleshoot the line with a serial analyzer and breakout box. If the problem continues, it is likely that there is a hardware problem.
If the problem does not continue, it is likely that there is a telephone company problem. Serial x is administratively down, line protocol is down. Router configuration includes the shutdown interface configuration command Duplicate IP address. Check the router configuration for the shutdown command.
Use the no shutdown interface configuration command to remove the shutdown command. If there are duplicate addresses, resolve the conflict by changing one of the IP addresses. Input rate to serial interface exceeds bandwidth available on serial link. Minimize periodic broadcast traffic such as routing and SAP updates by using access lists or by other means. For example, to increase the delay between SAP updates, use the ipx sap-interval interface configuration command.
Increase the output hold queue size in small increments for instance, 25 percent , using the hold-queue out interface configuration command. On affected interfaces, turn off fast switching for heavily used protocols.
For example, to turn off IP fast switching, enter the no ip route-cache interface configuration command. For the command syntax for other protocols, consult the Cisco IOS configuration guides and command references. Implement priority queuing on slower serial links by configuring priority lists. For information on configuring priority lists, see the Cisco IOS configuration guides and command references.
Input rate exceeds the capacity of the router or input queues exceed the size of output queues. Increase the output queue size on common destination interfaces for the interface that is dropping packets. Use the hold-queue out interface configuration command.
Increase these queues by small increments for instance, 25percent until you no longer see drops in the show interfaces output. Reduce the input queue size, using the hold-queue in interface configuration command, to force input drops to become output drops. Output drops have less impact on the performance of the router than do input drops.
The default input hold queue is 75 packets. Use a serial analyzer to isolate the source of the input errors. If you detect errors, it is likely that there is a hardware problem or a clock mismatch in a device that is external to the router. Use the loopback and ping tests to isolate the specific problem source. Look for patterns. For example, if errors occur at a consistent interval, they could be related to a periodic function such as the sending of routing updates.
Ensure that the line is clean enough for transmission requirements. Shield the cable if necessary. Make sure the cable is within the recommended length-no more than 50 feet Ensure that all devices are properly configured for a common line clock. Contact your leased-line or other carrier service and have it perform integrity tests on the line.
A framing error occurs when a packet does not end on an 8-bit byte boundary for one of the following reasons: Noisy serial line Improperly designed cable; serial cable is too long; the cable from the CSU or DSU to the router is not shielded SCTE mode is not enabled on the DSU; the CSU line clock is incorrectly configured; one of the clocks is configured for local clocking Ones density problem on T1 link incorrect framing or coding specification.
Make certain you are using the correct cable. Ensure that all devices are properly configured to use a common line clock. Aborts indicate an illegal sequence of one bits more than seven in a row. Make certain the cable is within the recommended length-no more than 50 feet Ensure that all connections are good. Check the hardware at both ends of the link.
Lower data rates and see if aborts decrease. Use local and remote loopback tests to determine where aborts are occurring. See the section "Special Serial Line Tests," later in this chapter.
When interface resets are occurring, examine other fields of the show interfaces serial command output to determine the source of the problem. Assuming that an increase in interface resets is being recorded, examine the following fields: If there is a high number of output drops in the show interfaces serial output, see the section "Serial Lines: Increasing Output Drops on Serial Link," earlier in this chapter. Check the carrier transitions field in the show interfaces serial display.
If carrier transitions are high while interface resets are being registered, the problem is likely to be a bad link or bad CSU or DSU. Contact your leased-line or carrier service and swap faulty equipment as necessary.
Examine the input errors field in the show interfaces serial display. Contact your leased-line or other carrier service and swap faulty equipment as necessary. The following problems can result in this symptom: Line interruptions due to an external source such as physical separation of cabling, red or yellow T1 alarms, or lightning striking somewhere along the network Faulty switch, DSU, or router hardware. Check hardware at both ends of the link. Attach a breakout box or a serial analyzer and test to determine source of problems.
If an analyzer or breakout box is unable to identify any external problems, check the router hardware.
Determine if the CSUs at both ends agree on the clock source local or line. If the CSUs do not agree, configure them so that they do. Usually the line is the source. If SCTE is not enabled on both ends of the connection, enable it. Make sure that ones density is maintained. Check with your leased-line provider for information on its framing and coding schemes.
If your carrier service uses AMI coding, either invert the transmit clock on both sides of the link or run the DSU in bit-stuff mode. Cable to router is out of specification. If the cable is longer than 50 feet If the cable is unshielded, replace it with shielded cable.
Indicates whether the interface hardware is currently active carrier detect is present or whether it has been taken down by an administrator. Indicates whether the software processes that handle the line protocol consider the line usable that is, keepalives are successful or whether it has been taken down by an administrator.
Specifies the internet address and subnet mask. Maximum transmission unit of the interface. Indicates the value of the bandwidth parameter that has been configured for the interface in kilobits per second. The bandwidth parameter is used to compute IGRP metrics only. If the interface is attached to a serial line with a line speed that does not match the default or for T1 and 56 for a standard synchronous serial line , use the bandwidth command to specify the correct line speed for this serial line.
Delay of the interface in microseconds. Encapsulation method assigned to the interface. Indicates whether loopback is set. Indicates whether keepalives are set.
Number of hours, minutes, and seconds since the last packet was successfully received by an interface. Useful for knowing when a dead interface failed. Number of hours, minutes, and seconds since the last packet was successfully transmitted by an interface.
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Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type. Showing results for. Search instead for. Did you mean:. All Community This category This board. Interface Resets? Hello - I have some x stacks that are dropping their 10g connections back to their main closets. Labels: Labels: Other Switching. Note : If there are multiple T1s into an access server, only one can be the primary, while the other T1s derive the clock from the primary.
In that case, verify that the T1 line designated as the primary clock source is configured correctly. Step 2 Set the T1 clock source correctly from the controller configuration mode.
Step 1 Check to see whether the linecoding configured on the port matches the framing format of the line. Use the show running-config command to check if isdn switchtype and pri-group timeslots are configured correctly. Contact your service provider for correct values. If the error counters do not increase but the problem persists, verify that the signaling channel is up and configured correctly. Step 1 Run the show interface serial x command, where x should be replaced by the interface number.
Step 2 Check to see if the interface is up. If the interface is not up, use the no shutdown command to bring the interface up.
Step 3 Ensure that encapsulation is PPP. If the interface is not using PPP, then use the encapsulation ppp command in the interface configuration mode to correct it. Step 4 Check to see whether loopback is set. Loopback should be set only for testing purposes. Use the no loopback command to remove loopbacks. Whenever troubleshooting a PRI, you need to check whether the T1 is running cleanly on both ends. If Layer 1 problems have been resolved, as described previously, we must look to Layer 2 and 3 problems.
The show isdn status command is used to display a snapshot of all ISDN interfaces. It displays the status of Layers 1, 2, and 3. Step 1 Verify that Layer 1 is active. Refer to the previous section "Is the Controller Administratively Down? Also verify that the T1 is not administratively down.
Use the no shutdown command to bring up the T1 controller. Refer to the section "Troubleshooting Using the show controller t1 Command. Use debug isdn q to verify that Layer 2 is stable. The debug isdn q command displays data link layer Layer 2 access procedures that are taking place at the router on the D-channel.
Ensure that you are configured to view debug messages by using the logging console or terminal monitor command as necessary.
Note In a production environment, verify that console logging is disabled. Enter the show logging command. If logging is enabled, the access server might intermittently freeze up as soon as the console port gets overloaded with log messages.
Enter the no logging console command. Note If debug isdn q is turned on and you do not receive any debug outputs, place a call or reset the controller to get debug outputs. Step 1 Verify that Layer 2 is stable. You should observe the debug outputs for messages indicating that the service is not bouncing up and down. If you see the following types of debug outputs, the line is not stable:. If Layer 2 does not appear to be stable, refer to the section "Troubleshooting Error Events.
This is usually seen when we are transmitting poll requests RRp and not getting a response from the switch RRf , or vice versa. Step 4 Verify that the D-channel is up using the show interfaces serial x command. If the D-channel is not up, then use no shutdown command to bring it up:. Step 5 Check to see whether encapsulation is PPP. If not, use the encapsulation ppp command to set encapsulation.
Step 6 Check to see whether the interface is in loopback mode. For normal operation, the interface should not be in loopback mode. Step 7 Power-cycle the router. The hardware loopback plug test can be used to test whether the router has any faults. If a router passes a hardware loopback plug test, then the problem exists elsewhere on the line.
Step 1 Use wire cutters to cut a working RJ or RJ cable so that there are 5 inches of cable and the connector attached to it. Step 2 Strip the wires. Step 3 Twist the wires from pins 1 and 4 together. Step 4 Twist the wires from pins 2 and 5 together. Pin 1 is the left-most pin when looking at the jack with the metal pins facing you. Step 1 Insert the plug into the T1 port in question. Step 2 Save your router configuration using the write memory command.
Step 4 Use the show running-config command to check whether the interface has an IP address. If the interface does not have an IP address, obtain a unique address and assign it to the interface with a subnet mask of Step 5 Clear the interface counters using the clear counters command.
Step 6 Perform the extended ping test as described in the "Using Extended ping Tests" section, earlier in this chapter. This section describes the techniques and procedures to troubleshoot E1 circuits for dial-in customers. The show e1 controller exec command provides information to logically troubleshoot physical layer and data link layer problems.
This section describes how to logically troubleshoot using the show controller e1 command. The information displayed is generally useful for diagnostic tasks performed by technical support personnel only. Issue a show controller e1 command to display statistics about the E1 link. Most E1 errors are caused by misconfigured lines. Ensure that linecoding, framing, clock source, and line termination balanced or unbalanced are configured according to what the service provider recommended. If the E1 line is not up, check to see that the line configuration is correct and matches the settings of the remote end.
Check the framing of the line and the remote end. Check the linecoding of the line and the remote end. Check whether the line termination is set for balanced or unbalanced 75 ohm or ohm. Consult your service provider for more information regarding the correct settings. Make any changes as necessary to both local or remote end devices. If the E1 controller and line are not up, check to see whether you are seeing one of the following messages in the show controller e1 exec output:.
You can check the framing format of the controller from the running configuration or the show controller e1 command output. If this does not fix the problem, proceed to the receiver has loss of signal section below.
Step 3 Check the framing format on the remote end. Step 4 Check the linecoding on the remote end. Step 1 Make sure that the cable between the interface port and the E1 service provider's equipment or E1 terminal equipment is connected correctly. Check to see whether the cable is hooked up to the correct ports. Correct the cable connections if necessary. The pins on a RJ jack are numbered from 1 through 8. Refer to Figure for more information. Step 5 Check to see whether there are far-end block errors.
If so, the problem exists with the receive lead on the local end. Contact TAC for more assistance. Run the show controller e1 exec command after each step to check whether the controller exhibits any errors. Check to see whether the line is in loopback mode from the show controller e1 output. Check the show controller command output to see whether any alarms are displayed by the controller. A received remote alarm means that an alarm is occurring on the line upstream of the equipment connected to the port.
Step 2 Check the linecoding setting on the remote-end equipment. Contact your service provider for the correct settings. Correct any misconfigurations, as necessary. Step 3 Insert an external loopback cable into the port. To create a loopback plug, refer to the section "Performing Hardware Loopback Plug Test," earlier in the chapter. Step 4 Check to see whether there are any alarms. Step 5 Remove the loopback plug and reconnect your E1 line.
Step 6 Check the cabling. Step 8 Connect the E1 line to a different port. If the problem does not persist, then the fault lies with the port:. A red alarm is declared when the CSU cannot synchronize with the framing pattern on the E1 line. Step 5 Connect the E1 line to a different port. The show controller e1 exec command provides error messages that can be used to troubleshoot problems.
To see whether the error counters are increasing, execute the show controller e1 command repeatedly. The presence of slips on E1 lines indicates a clocking problem. The E1 provider telco will provide the clocking that the customer premises equipment CPE will need to synchronize to. This can be ascertained by looking for "Clock Source is Line Primary. Note If there are multiple E1s into an access server, only one can be the primary, while the other E1s derive the clock from the primary.
In that case, verify that the E1 line designated as the primary clock source is configured correctly. Step 2 Set the E1 clock source correctly from the controller configuration mode. Use the show running-config command to check whether isdn switchtype and pri-group timeslots are configured correctly.
To change the isdn switchtype and pri-group , use these lines:. Step 2 Check to see whether the interface is up. If the interface is not up, use the no shutdown command to bring up the interface. Whenever troubleshooting a PRI, you need to check whether the E1 is running cleanly on both ends. Refer to the section "Is the Controller Administratively Down? Also verify that the E1 is not administratively down.
Use the no shutdown command to bring up the E1 controller. Refer to the previous section "Troubleshooting Using the show controller e1 Command," and the upcoming section "Troubleshooting E1 Error Events. Ensure that you are configured to view debug messages by using the logging console or terminal monitor commands, as necessary. If Layer 2 does not appear to be stable refer to the "Troubleshooting Error Events" section, earlier in this chapter. Downloads Troubleshooting Serial Lines.
Is the Line Up? Caution Because debugging output is assigned high priority in the CPU process, it can render the system unusable. When you finish using a debug command, remember to disable it with its specific no debug command or with the no debug all command. Caution In general, do not adjust system buffers unless you are working closely with a Cisco technical support representative.
You can severely affect the performance of your hardware and your network if you incorrectly adjust the system buffers on your router. Router show interfaces serial. Internet address is Encapsulation HDLC, loopback not set, keepalive set 10 sec. Enter configuration commands, one per line. Mar 20 Clear "show interface" counters on all interfaces [confirm].
Contacts Feedback Help Site Map. This is the proper status line condition. No action is required. Cabling is faulty or incorrect. A local or remote router is misconfigured. Keepalives are not being sent by the remote router. Router hardware local or remote has failed. A high error rate has occurred due to a telephone company service problem. Router hardware interface is bad.
A duplicate IP address exists. Input rate to serial interface exceeds bandwidth available on serial link. Framing errors frame. Aborted transmission abort. Assuming that an increase in interface resets is being recorded, examine the following fields: 1.
Incorrect CSU configuration. Incorrect DSU configuration. Start by enabling debugging. Configuring the interface on R2. R2 conf terminal Enter configuration commands, one per line.
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