Catalyst 6500 Series Switch SIP, SSC, and SPA Software Configuration Guide

Serial x is up, line protocol is up

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This is the proper status line condition. No action is required.

Serial x is down, line protocol is down

The switch is not sensing a carrier detect (CD) signal (that is, the CD is not active).

The line is down or is not connected on the far end.

Cabling is faulty or incorrect.

Hardware failure has occurred (CSU/DSU).

1. Check the CD LEDs to see whether the CD is active, or insert a breakout box on the line to check for the CD signal.

2. Verify that you are using the proper cable (see your hardware installation documentation).

3. Insert a breakout box and check all control leads.

4. Contact your leased-line or other carrier service to see whether there is a problem.

5. Swap faulty parts.

6. If you suspect faulty switch 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

A local or remote switch is misconfigured.

Keepalives are not being sent by the remote router.

A leased-line or other carrier service problem has occurred (noisy line or misconfigured or failed switch).

A timing problem has occurred on the cable.

A local or remote CSU/DSU has failed.

Router hardware (local or remote) has failed.

1. Put the line in local loopback mode and use the show interfaces serial command to determine whether the line protocol comes up.

Note If the line protocol comes up, a failed remote device is the likely problem.

This solution will only work with HDLC encapsulation. For FR and PPP encapsulation a looped interface will always have the line protocol down. In addition, you may need to change the encapsulation to HDLC to debug this issues.

2. If the problem appears to be on the remote end, repeat Step 1 on the remote interface.

3. Verify all cabling. Make certain that the cable is attached to the correct interface, the correct CSU/DSU, and the correct remote termination point.

4. Enable the debug serial interface exec command.

Note First enable per- interface debugging using the debug interface serial x command. Depending on the encapsulation, also enable the corresponding debug.

HDLC: debug serial interface
PPP: debug ppp negotiation
FR: debug frame-relay lmi

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Caution Because debugging output is assigned high priority in the CPU process, it can cause the system to become unusable. For this reason, use debug commands only to troubleshoot specific problems or during troubleshooting sessions with Cisco technical support staff. You should use debug commands during periods of lower network traffic and fewer users. Debugging during these periods decreases the likelihood that increased debug command processing overhead will affect system use.

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5. 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 switch hardware problem is likely. Swap switch interface hardware.

6. If the line protocol comes up and the keepalive counter increments, the problem is not in the local switch. Troubleshoot the serial line, as described in the sections "Troubleshooting Clocking Problems" and "CSU and DSU Loopback Tests," later in this chapter.

7. If you suspect faulty switch hardware, change the serial line to an unused port. If the connection comes up, the previously connected interface has a problem.

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.

1. Use the show running-config privileged exec command to look for any loopback interface configuration command entries.

2. If you find a loopback interface configuration command entry, use the no loopback interface configuration command to remove the loop.

3. If you do not find the loopback interface configuration command, examine the CSU/DSU to determine whether they are configured in manual loopback mode. If they are, disable manual loopback.

4. Reset the CSU or DSU, and inspect the line status. If the line protocol comes up, no other action is needed.

5. 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)

A high error rate has occurred due to a remote device problem.

A CSU or DSU hardware problem has occurred.

Switch hardware (interface) is bad.

1. Troubleshoot the line with a serial analyzer and breakout box.
Examine the output of
show controller T1 or
show controller T3 or
show controller serial x depending on whether the SPA is a T1/E1 or CT3 or T3/E3.

2. Loop CSU/DSU (DTE loop). 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.

3. Swap out bad hardware, as required (CSU, DSU, switch, local or remote switch).

Serial x is administratively down, line protocol is down

The switch configuration includes the shutdown interface configuration command.

A duplicate IP address exists.

1. Check the switch configuration for the shutdown command.

2. Use the no shutdown interface configuration command to remove the shutdown command.

3. Verify that there are no identical IP addresses using the show running-config privileged exec command or the show interfaces exec command.

4. 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

1. Minimize periodic broadcast traffic, such as routing and SAP¹ 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.

2. Increase the output hold queue size in small increments (for instance, 25 percent), using the hold-queue out interface configuration command.

3. 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.

Note: Output drops are acceptable under certain conditions. For instance, if a link is known to be overused (with no way to remedy the situation), it is often considered preferable to drop packets than to hold them. This is true for protocols that support flow control and can retransmit data (such as TCP/IP and Novell IPX² ). However, some protocols, such as DECnet and local-area transport, are sensitive to dropped packets and accommodate retransmission poorly, if at all.

¹ SAP = Service Advertising Protocol

² IPX = Internetwork Packet Exchange

Input rate exceeds the capacity of the switch, or input queues exceed the size of output queues

Note: Input drop problems are typically seen when traffic is being routed between faster interfaces (such as Ethernet, Token Ring, and FDDI¹ ) and serial interfaces. When traffic is light, there is no problem. As traffic rates increase, backups start occurring. Switches drop packets during these congested periods.

1. Increase the output queue size on common destination interfaces for the interface that is dropping packets. Use the hold-queue number out interface configuration command. Increase these queues by small increments (for instance, 25 percent) until you no longer see drops in the show interfaces output. The default output hold queue limit is 40 packets.

2. Reduce the input queue size, using the hold-queue number in interface configuration command, to force input drops to become output drops. Output drops have less impact on the performance of the switch than do input drops. The default input hold queue is 75 packets.

¹ FDDI = Fiber Distributed Data Interface

The following problems can result in this symptom:

•Faulty telephone company equipment

•Noisy serial line

•Incorrect clocking configuration

•Incorrect cable or cable that is too long

•Bad cable or connection

•Bad CSU or DSU

•Bad switch hardware

•Data converter or other device being used between switch and DSU

Note: Cisco strongly recommends against the use of data converters when you are connecting a switch to a WAN or a serial network.

1. Use a serial analyzer to isolate the source of the input errors. If you detect errors, there likely is a hardware problem or a clock mismatch in a device that is external to the switch.

2. Use the loopback and ping tests to isolate the specific problem source. For more information, see the sections "Using Extended ping Tests" and "CSU and DSU Loopback Tests," later in this chapter.

3. 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.

CRC errors (CRC)

CRC errors occur when the CRC calculation does not pass (indicating that data is corrupted) for one of the following reasons:

•The serial line is noisy.

•The serial cable is too long, or the cable from the CSU/DSU to the switch is not shielded.

•SCTE mode is not enabled on DSU.

•The CSU line clock is incorrectly configured.

•A ones density problem has occurred on the T1 link (incorrect framing or coding specification).

1. Ensure that the line is clean enough for transmission requirements. Shield the cable, if necessary.

2. Make sure that the cable is within the recommended length (no more than 50 feet [15.24 meters], or 25 feet [7.62 meters] for a T1 link).

3. Ensure that all devices are properly configured for a common line clock. Set SCTE on the local and remote DSU. If your CSU/DSU does not support SCTE, see the section "Inverting the Transmit Clock," later in this chapter.

4. Make certain that the local and remote CSU/DSU are configured for the same framing and coding scheme as that used by the leased-line or other carrier service (for example, ESF/B8ZS).

5. Contact your leased-line or other carrier service, and have it perform integrity tests on the line.

Framing errors (frame)

A framing error occurs when a packet does not end on an 8-bit byte boundary for one of the following reasons:

•The serial line is noisy.

•The cable is improperly designed; the serial cable is too long; the cable from the CSU or DSU to the switch 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.

•A ones density problem has occurred on the T1 link (incorrect framing or coding specification).

1. Ensure that the line is clean enough for transmission requirements. Shield the cable, if necessary. Make certain that you are using the correct cable.

2. Make sure that the cable is within the recommended length (no more than 50 feet [15.24 meters], or 25 feet [7.62 meters] for a T1 link).

3. Ensure that all devices are properly configured to use a common line clock. Set SCTE on the local and remote DSU. If your CSU/DSU does not support SCTE, see the section "Inverting the Transmit Clock," later in this chapter.

4. Make certain that the local and remote CSU/DSU is configured for the same framing and coding scheme as that used by the leased-line or other carrier service (for example, ESF¹ /B8ZS² ).

5. Contact your leased-line or other carrier service, and have it perform integrity tests on the line.

Aborted transmission (abort)

Aborts indicate an illegal sequence of 1 bit (more than seven in a row)

The following are possible reasons for this to occur:

•SCTE mode is not enabled on DSU.

•The CSU line clock is incorrectly configured.

•The serial cable is too long, or the cable from the CSU or DSU to the switch is not shielded.

•A ones density problem has occurred on the T1 link (incorrect framing or coding specification).

•A packet terminated in middle of transmission (typical cause is an interface reset or a framing error or a buffer overrun).

•A hardware problem has occurred (bad circuit, bad CSU/DSU, or bad sending interface on remote switch).

1. Ensure that all devices are properly configured to use a common line clock. Set SCTE on the local and remote DSU. If your CSU/DSU does not support SCTE, see the section "Inverting the Transmit Clock," later in this chapter.

2. Shield the cable, if necessary. Make certain that the cable is within the recommended length (no more than 50 feet [15.24 meters], or 25 feet [7.62 meters] for a T1 link). Ensure that all connections are good.

3. Check the hardware at both ends of the link. Swap faulty equipment, as necessary.

4. Lower data rates and determine whether aborts decrease.

5. Use local and remote loopback tests to determine where aborts are occurring (see the section "Special Serial Line Tests," later in this chapter).

6. Contact your leased-line or other carrier service, and have it perform integrity tests on the line.

¹ ESF = Extended Superframe Format

² B8ZS = binary eight-zero substitution

The following problems can result in this symptom:

•Congestion on link (typically associated with output drops)

•Bad line causing CD transitions

•Possible hardware problem at the CSU, DSU, or switch

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:

1. 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.

2. 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 a bad CSU or DSU. Contact your leased-line or carrier service, and swap faulty equipment, as necessary.

3. Examine the Input Errors field in the show interfaces serial display. If input errors are high while interface resets are increasing, the problem is probably a bad link or a bad CSU/DSU. 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 switch hardware

1. Check hardware at both ends of the link (attach a breakout box or a serial analyzer, and test to determine the source of problems).

2. If an analyzer or breakout box is incapable of identifying any external problems, check the switch hardware.

3. Swap faulty equipment, as necessary.

BERT test result (running)

Indicates the current state of the test. In this case, "running" indicates that the BER test is still in progress. After a test is completed, "done" is displayed.

Test Pattern : 2^15, Status : Sync, Sync Detected : 1

Indicates the test pattern you selected for the test (2^15), the current synchronization state (sync), and the number of times synchronization has been detected during this test (1).

Interval : 5 minute(s), Time Remain : 5 minute(s)

Indicates the time the test takes to run and the time remaining for the test to run.

If you terminate a BER test, you receive a message similar to the following:

Interval : 5 minute(s), Time Remain : 2 minute(s) (unable to complete)

"Interval: 5 minutes" indicates the configured run time for the test. "Time Remain : 2 minutes" indicates the time remaining in the test prior to termination. "(Unable to complete)" signifies that you interrupted the test.

Bit Errors(Since BERT Started): 6 bits, Bits Received(Since BERT start): 8113 Kbits
Bit Errors(Since last sync): 6 bits
Bits Received(Since last sync): 8113 Kbits

These four lines show the bit errors that have been detected versus the total number of test bits that have been received since the test started and since the last synchronization was detected.

Router# configure terminal

Enters global configuration mode.

T3/E3

Router(config)# interface serial slot/subslot/port

T1/E1

Router(config)# controller slot/subslot/port

Selects the interface to configure.

•slot/subslot/port—Specifies the location of the interface.

•slot/subslot/port—Specifies the location of the T1/E1 controller.

T3/E3

Router(config-if)# loopback {local | dte | network {line | payload} | remote}

T1/E1

Router(config-controller)# loopback {local [line | payload] | diag}

Specifies the loopback mode.

•local—Loopback after going through the framer toward the terminal.

•dte—Loopback after the LIU towards the terminal.

•network—Loopback towards the network.

•remote—Send FEAC to set remote in loopback.

•line—Loopback toward network before going through framer.

•payload—Loopback toward network after going through framer.

•diag—Loopback after going through the HDLC controller towards the terminal.