Blog: Basic Network Troubleshooting and Ping


Posted on June 8th, by Michael Maniscalco in Blog. No Comments

More commonly than I would have ever imagined we receive questions about “basic device checks” within the ihiji invision system. These basic checks will tell integrators whether a device online/offline but more commonly it is exposing network problems such as high latency or dropped packets. These are real issues which can often time be difficult to troubleshoot but in my recent experience I think there is more of a lack of understanding on the basic, yet valuable, information that ping can tell us.

My opinion is that every field technician who touches a network connected devices needs to understand what an IP address, gateway, subnet and DNS server are and also understand the basics of ping. So, rather than re-write the book, I wanted to share a few resources that Google pulled up for me. I hope this helps!

So what is ping?
This is from Ping on Wikipedia.

Ping is a computer network administration utility used to test the reachability of a host on an Internet Protocol (IP) network and to measure the round-trip time for messages sent from the originating host to a destination computer. The name comes from active sonar terminology which sends a pulse of sound and listens for the echo.

Ping operates by sending Internet Control Message Protocol (ICMP) echo request packets to the target host and waiting for an ICMP response. In the process it measures the time from transmission to reception (round-trip time)[1] and records any packet loss. The results of the test are printed in the form of a statistical summary of the response packets received, including the minimum, maximum, and the mean round-trip times, and sometimes the standard deviation of the mean.

Depending on the implementation, the ping command can be run with various command line switches to enable special operational modes. Example options include: specifying the packet size used as the probe, automatic repeated operation for sending a specified count of probes, and time stamping.

That’s cool but what does ping tell me?
The following is an excerpt from “What On Earth Is Ping” Blog

Ok, still don’t understand what ping is?

Right I guess some of you are not technical that is why you are on this site. The best analogy that I can think off for ping is; say you are at home and you want to get a newspaper from the shop, the shop is about 3 miles away, so you get in your car. It takes about 10 mins to get to the shops, 2 mins to buy the paper and another 10 mins to get back to your house. The total journey time is 22 minutes. The same concept applies ping. The packet is generated by your PC and sent into the internet cloud, and the destination (being another PC, server, switch or router) receives this ICMP packet processes it and sends it back with an ICMP response.

Obviously depending where you are sending a ICMP packet around the world will tell you how much delay you will get in your response times. If you pinging within your country and it has a good internet infrastructure response times should be quicker than if your pinging to a different country as the ICMP packet has to travel a greater distance.

Right I sort of get ping, how do I do it from my Windows PC?
Enough talk about ping. First we need to get a command prompt open. If your using Windows, most versions have the “run” function.

So click on Start (or Windows Symbol Left hand side) > Run > Type cmd in the box then hit OK or Enter.

A black screen should appear before you. Now we need to find an IP address to ping. You can find a website address to ping to see if the web server responds back with an ICMP packet. In the example below, we can see a response from www.cisco.com. Simply type ping www.cisco.com (or any other website you want), hopefully you will see four lines of response saying the Cisco Webserver is there and how long is took (ms = milliseconds). In this example the four ICMP packets took around 125ms to get to the Cisco webserver and back to my PC.

C:\Documents and Settings>ping www.cisco.com

Pinging e144.cd.akamaiedge.net [84.53.164.170] with 32 bytes of data:

Reply from 84.53.164.170: bytes=32 time < 125ms TTL=128
Reply from 84.53.164.170: bytes=32 time < 135ms TTL=128
Reply from 84.53.164.170: bytes=32 time < 125ms TTL=128
Reply from 84.53.164.170: bytes=32 time < 125ms TTL=128

Ping statistics for 10.163.2.169:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 125ms, Maximum = 135ms, Average = 126ms

Note: Some websites you might not be able to ping for security reasons, and get a “Request time out” message. This is due to a Firewall being present which blocks ICMP packets. A firewall is a security device that prevents attacks or viruses entering your computer network and often can be standard practise that firewalls blocks ICMP packets.

Conclusion about ping
I hope I have given some insight into ping for some people who are not technical. There are more advanced functions of ping that you can use. You can research more advanced techniques of ping at our sister site “How to Ping” (coming soon). I wish you well in your first step into Internet networking by utilising the ping function.

Ping Parameters
My next suggestion is that you become intimately familiar with the ping options. This is easy, every computer typically has ping pre-installed. Here’s a summary of the most common ping parameters defined by an overview of the ping options from Microsoft.

Syntax
ping [-t] [-a] [-n Count] [-l Size] [-f] [-i TTL] [-v TOS] [-r Count] [-s Count] [{-j HostList | -k HostList}] [-w Timeout] [TargetName]

Parameters
-t : Specifies that ping continue sending Echo Request messages to the destination until interrupted. To interrupt and display statistics, press CTRL-BREAK. To interrupt and quit ping, press CTRL-C.

-a : Specifies that reverse name resolution is performed on the destination IP address. If this is successful, ping displays the corresponding host name.

-n Count : Specifies the number of Echo Request messages sent. The default is 4.

-l Size : Specifies the length, in bytes, of the Data field in the Echo Request messages sent. The default is 32. The maximum size is 65,527.

-w Timeout : Specifies the amount of time, in milliseconds, to wait for the Echo Reply message that corresponds to a given Echo Request message to be received. If the Echo Reply message is not received within the time-out, the “Request timed out” error message is displayed. The default time-out is 4000 (4 seconds).

TargetName : Specifies the destination, which is identified either by IP address or host name.

/? : Displays help at the command prompt.

Packet Loss
So, once you get pings and some responses, the easiest thing to look at is packet loss. Here’s some information on packet loss from wikipedia.

Packet loss occurs when one or more packets of data travelling across a computer network fail to reach their destination. Packet loss is distinguished as one of the three main error types encountered in digital communications; the other two being bit error and spurious packets caused due to noise.

Causes
Packet loss can be caused by a number of factors including signal degradation over the network medium due to multi-path fading, packet drop because of channel congestion [1][2], corrupted packets rejected in-transit, faulty networking hardware, faulty network drivers or normal routing routines (such as DSR in ad-hoc networks [3]).
[edit]Effects

When caused by network problems, lost or dropped packets can result in highly noticeable performance issues or jitter with streaming technologies, voice over IP, online gaming and videoconferencing, and will affect all other network applications to a degree. [4] However, it is important to note that packet loss does not always indicate a problem. If the latency and the packet loss at the destination hop are acceptable then the hops prior to that one don’t matter. [5]

Packet Latency
Now, what does all of the information mean? Well, if ping is working and you’re getting replies, you want to look at latency. Here’s a great summary of ping latency from the Ping Timed Out Blog.

Bandwidth is just one element of what a person perceives as the speed of a network. Latency is another element that contributes to network speed. The term latency refers to any of several kinds of delays typically incurred in processing of network data. A so-called low latency network connection is one that generally experiences small delay times, while a high latency connection generally suffers from long delays.

Latency vs. Bandwidth
Although the theoretical peak bandwidth of a network connection is fixed according to the technology used, the actual bandwidth you will obtain varies over time and is affected by high latencies. Excessive latency creates bottlenecks that prevent data from filling the network pipe, thus decreasing effective bandwidth. The impact of latency on network bandwidth can be temporary (lasting a few seconds) or persistent (constant) depending on the source of the delays.

Latency of Satellite Internet Service
Satellite Internet service illustrates the difference between latency and bandwidth on computer networks. Satellite Internet connections possess both high bandwidth and high latency. When loading a Web page, for example, most satellite users can observe a noticeable delay from the time they enter a Web address to the time the page begins loading. This high latency is due primarily to propagation delay as the request message travels at the speed of light to the distant satellite station and back to the home network. Once the messages arrive on Earth, however, the page loads quickly like on other high-bandwidth Internet connections (DSL or cable).

Besides propagation delays, latency also may also involve transmission delays (properties of the physical medium) and processing delays (such as passing through proxy servers or making network hops on the Internet).

Measuring Network Latency
Network tools like ping tests and traceroute measure latency by determining the time it takes a given network packet to travel from source to destination and back, the so-called round-trip time. Round-trip time is not the only way to specify latency, but it is the most common.
On DSL or cable Internet connections, latencies of less than 100 milliseconds (ms) are typical and less than 25 ms desired. Satellite Internet connections, on the other hand, average 500 ms or higher latency.

Summary
Two key elements of network performance are bandwidth and latency. The average person is more familiar with the concept of bandwidth as that is the one advertised by manufacturers of network equipment. However, latency matters equally to the end user experience as the behavior of satellite Internet connections illustrates. Businesses use the term Quality of Service (QoS) to refer to measuring and maintaining consistent performance on a network by managing both bandwidth and latency in a coordinated fashion.

Going Beyond Ping (Or Sometimes Before You Ping)
Lastly, here is a good check list from Microsoft on troubleshooting basic networking connectivity

Local Connectivity

Another aspect of verifying network connectivity involves a check of the local area connection. Ensure that you are connected to the network and that the Internet Protocol (IP) addresses are correct. Do this by using the IPConfig command-line tool. The IPConfig tool is used to view and modify IP configuration details used by the computer. With DNS dynamic updates, you can also use IPConfig to register the computer’s entries in the DNS service.

To view IP configuration details

Type ipconfig /all at the command prompt and then press ENTER.

Look through the output. Check the following:

Do you have an IP address?

Do you have a default gateway?

Do you have a DHCP server?

Use the Ping tool to determine whether you have network connectivity to the default gateway and to the DHCP server.

To test a TCP/IP connectivity by using the ping command

At the command prompt, ping the loopback address by typing the following:
127.0.0.1
If the ping command fails, verify that the computer was restarted after TCP/IP was installed and configured.

Ping the IP address of the computer.
If the ping command fails, restart the computer and check the routing table using the route print command.

Ping the IP address of the default gateway.
If the ping command fails, verify that the default gateway IP address is correct and that the gateway (router) is operational.

Ping the IP address of a remote host (a host that is on a different subnet).
If the ping command fails, verify that the remote host IP address is correct, that the remote host is operational, and that all gateways (routers) between this computer and the remote host are operational.

Ping the IP address of the DNS server.
If the ping command fails, verify that the DNS server IP address is correct, that the DNS server is operational, and that all gateways (routers) between this computer and the DNS server are operational.

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