Verizon Technical Information Document

 

 

Procedure for Performing a Ping Test on a Cisco Serial Line

 

 

 

PURPOSE

 

An instructional document detailing instructions for performing a ping test on a serial line connected to a Cisco router.  This document also gives examples of two useful types of ping tests: the all-zeroes 1500-byte ping test and the all-ones 1500-byte ping test.

 

 

BACKGROUND

 

A ping test is a useful diagnostic tool used on Cisco internetworking devices and on many host systems.  In the TCP/IP protocol, this tool is also known as an Internet Control Message Protocol echo request, or ICMP for short.  A ping test is particularly useful when a circuit is showing a large number of input errors, such as when performing a Cisco router command such as show interfaces serial.

 

Cisco utilizes a ping command that, by default, will send 20 ping packets of size 100 bytes each, one after the other.  However, when troubleshooting a serial line connected to a Cisco router, it is helpful to run a ping test with a larger data packet, 1500 bytes, and with a greater number of successive packets, such as 100 or 1000.  This will provide a higher amount of accuracy in diagnosing circuit issues.

 

 

INSTRUCTIONS

 

To perform a ping test on a Cisco serial line, follow these instructions:

 

1.    Put the CSU or the DSU on the serial line into local loopback mode.

2.   To do a successful ping test, it is important to send pings consisting of different packet sizes and different data patterns.  Two simple and useful ping patters to use are the all-zeros pattern and the all-ones pattern.

 

To configure a ping test using the all-zeroes data pattern, which is a ping sent using a data packet consisting of a hexadecimal 0x0000 pattern, enter the command ping at the router prompt, and enter the following information on screen as you are prompted:

 

Target IP address:  The IP address to which you want to send the ping pattern.

Protocol [ip]:  Press enter (The default value of IP).

Repeat count:  100  (This sends the ping pattern one hundred times).

Datagram size:  1500 (This is a 1500-byte ping packet).

Timeout in seconds (2):  Press enter (The default value of 2 seconds).

Extended commands [n]:  Y

Source address:  The IP address from which you are sending the ping.

Type of service [0]:  Press enter  (default value of 0).

Set DP bit in IP header? [no}:  Press enter (default value of no).

Validate reply data? [no]:  Press enter (default value of no).

Data Pattern [0xABCD}:  0x0000

Loose, Strict, Record, Timestamp, Verbose [none]:  Press enter (default value of no).

Sweep range of sizes [n]:  Press enter (default value of no).

 

Then the screen will show that you are sending 100, 1500-byte ping packets.  If the ping is successful, you will see a series of exclamation points.  If you see one or more periods instead of exclamation points, then some or all of the ping packets have failed to transmit. 

 

3.   The ping test adds a controlled amount of traffic to the line to determine if this traffic has increased the number of input errors or clocking errors on the line.  If before running the ping test, you determined the number of input errors on the line by running a command such as show interfaces serial, then you can run that same test to determine if the number of errors has increased after running the ping test.  If the number of errors on the line has increased, then there is potentially either a physical issue with the cable or DSU/CSU, or else a potential clocking error with the DSU/CSU unit.  If the number of errors has not increased after running the ping test, then the equipment on the circuit is most likely in good condition and not the source of any errors.

 

4.   Next, configure another ping test using the all-ones data pattern, which is a ping sent using a data packet consisting of a hexadecimal 0xFFFF pattern.  This tests the circuit by entering ping packets of higher payload than the all-zeroes ping test.

 

Enter the command ping at the router prompt, and enter the following information on screen as you are prompted:

 

Target IP address:  The IP address to which you want to send the ping pattern.

Protocol [ip]:  Press enter (The default value of IP).

Repeat count:  100  (This sends the ping pattern one hundred times).

Datagram size:  1500 (This is a 1500-byte ping packet).

Timeout in seconds (2):  Press enter (The default value of 2 seconds).

Extended commands [n]:  Y

Source address:  The IP address from which you are sending the ping.

Type of service [0]:  Press enter  (default value of 0).

Set DP bit in IP header? [no}:  Press enter (default value of no).

Validate reply data? [no]:  Press enter (default value of no).

Data Pattern [0xABCD}:  0xffff

Loose, Strict, Record, Timestamp, Verbose [none]:  Press enter (default value of no).

Sweep range of sizes [n]:  Press enter (default value of no).

 

Again, the screen will show that you are sending 100, 1500-byte ping packets.  If the ping is successful, you will see the series of exclamation points, or one of more periods if any ping did not transmit successfully.

 

Once again, you can examine the output of a show interfaces serial command to determine if the number of input errors on the line has increased.

 

 

5.    If you see an increase in error statistics from either the all-zeroes or all-ones ping test, then you most likely have an issue with the serial line itself, or the DSU/CSU unit.  Swap out the DSU/CSU unit and run the ping tests again.  If the errors do not increase this time, then the problem was a defective DSU/CSU.  Decommission the defective unit.  If the errors continue to increase after replacing the hardware unit, then swap out the cable with a new cable, and run the test again.

 

6.    If the errors continue to persist, then contact your technical services representative.

 

 

 

 

 

FIGURES

 

 

Figure 1:  Example of a successful all-zeros ping test:

 

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Figure 2:  Example of a successful all-ones ping test:

 

 

 

 

 

 

 

Author:  James Sanders

 

Date:  July 11, 2017