How To Troubleshoot Cisco Debug Serial Port Issues

This user guide will help you if you have a cisco debug serial port.


Local CSU and DSU loopback tests for HDLC or PPP links

Remote CSU and DSU loopback tests for HDLC or PPP links

Troubleshooting Serial Lines

cisco debug serial interface

This chapter provides general troubleshooting information and a discussion of how to troubleshoot the Serial Partner. The chapter consists of sections after name=”wp1020547″>:

Troubleshooting Use The Real Show Interfaces Serial Command

The output of the “show Interfaces Serial Exec” command displays information related to serial interfaces. On fig. Figure 15-1 shows the output of the show Interfaces Serial Exec command from behind the serial link control interface High Level Data (HDLC).

cisco debug serial interface

This section describes how to use the show user interface serial command to diagnose serial connection problems in a wide area network (WAN) environment. The following sections describe some of the important fields in the output of the command.

Other branches displayed on the screen are detailed in the “Details of Serial Command Display Interfaces” section later in this chapter.

Serial Lines: Displays The Line Status Of The Interface’s Serial Interface.

You can view five potential problem states in the interface title bar of the Serialized Interfaces screen (see Figure 15-1):


Table 15-1 shows interface status conditions, possible problems with the conditions, and the results of those problems.

Serial Lines: Increased Output Loss In Serial Connection.

The output usually appears in the output of the show Interfaces serial command (see Figure 15-1) because the system is trying to forward the packet to the active buffer, but the buffer is not available.

In Table. Table 15-2 highlights possible problems that can cause this symptom and describes solutions that can solve this problem.

Serial Lines: Increased The Amount Of Input Data On A Serial Connection.

An entry appears in the output of any show interface that the executive reports to it (see Figure 15-1) when too many packets are being processed on the system from that interface.

In Table. Table 15-3 describes all possible problems that can cause this symptom, and provides solutions for this particular problem.

Serial Lines: More Than 1% Increase In Input Errors Of All Interface Traffic

When a series of errors occur in the serial output of show interfaces (see Figure 15-1), there can be several possible reasons for such backtracking. The most likely sources are listed in Table 15-4.

Note Any estimates ignore CRC (double check cyclic redundancy check), framing errors, gaps, 1 The % of all interface traffic indicates some sort of connectivity problem that should be isolated and fixed.

Symptom: An increase in the number of typos that exceeds 1% of the total program traffic

Serial Lines: Troubleshooting Serial Line Input Errors

In Table. 15-5 describes the various error input options displayedWith the new show Interfaces Serial command (see Figure 15-1), possible problems that may still cause errors and solutions to these problems.

Serial Lines: Increased The Number Of Interface Resets On A Serial Connection.

The interface starts that appear in the output of all show interface serial statements (see Figure 15-1) are the result of missing keepalive packets.

In Table. Figures 15-6 show fixable problems that can cause this problem, and the symptom describes solutions for each of these problems.

Serial Lines: Increasing Carrier Crossovers For Serial Links

Carrier transitions are present in the serial output of the showcase interfaces Exec command whenever an interruption of the pet carrier signal occurs at that point (, completely resetting the interface at the end of a specific link type).

In Table. 15-7 describes the possible problems that this symptom can cause and how to fix them.


Use The Show Game Controllers Command

The show controllers execute command is another important diagnostic package when troubleshooting serial lines. Syntax checking is platform dependent:

•alt=”” src=”../../../../i/templates/blank.gif”>Use for serial interfaces to routers Cisco 7000 exec Serial Controller cbus command performance.

For the current AGS, CGS, and MGS, use the show mci exec controller command.

On fig. 15-2 shows the output obtained from the control of the Cbus-Exec controller. This command is used on Cisco 7000 series routers with a Fast Serial Interface Processor (FSIP) board. Check the command output to make sure the cableThe Guide Service Unit/Digital Service Unit (CSU/DSU) is connected to the correct port. You can also check the firmware version to make sure it’s up to date.

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