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Troubleshooting Network Latency

One of the first things people often assume when they're unable to reach their websites or email is that the server their account is on is down. What they don't realize is that there are a great deal of other factors that may be causing a disruption of service.

Conceived by the U.S. government's Advanced Research Projects Agency (ARPA), the Internet(not to be confused with the World Wide Web) is the largest computer network that has ever existed. The Internet consists of countless smaller internets (notice the small "i") that, put simply, enable users to access information on other computers.

The following diagram is a simplified representation of the path information travels from your computer (the client) to the computer your website and/or email resides on (the server). All of the hardware (besides the client machine) above the globe is owned by your dial-up provider. Note: Even if you use DSL, a cable modem or an ISDN line, the ISP's network will be similar to the one depicted in the diagram. The hardware below the globe resides on the Internet Connection network.

One very simplified diagram of the Internet

Network Troubleshooting Tools

To help you isolate the source of network problems you can employ two useful tools - ping and traceroute.

Ping

Ping is a useful tool for testing to see if a host is responding, among other things.

On machines running Windows 95, 98, ME or 2000, ping can be accessed via a DOS prompt. Select "Run..." from the Start menu and type "command" ("cmd" for Win2K) or click on the MS-DOS Prompt shortcut in your Start Menu. Once you're at the DOS prompt, type "ping Host-Address*".

For users of MacOS, MacTCP Ping is a great utility. More options include IPNetMonitor and WhatRoute. Please refer to your software's documentation for information on using ping.

For those who use *nix systems (BSD, Linux, Solaris etc.), ping should have been installed with the OS. Access it by typing "ping Host-Address*" at your command line.

*Note: Due to the configuration of our network, you will not be able to ping or traceroute directly to your account. Instead, you will have to ping use the address "router.dmvnoc.com" for these tools.

This program uses the Internet Message Control Protocol (IMCP) to send data packets to a host you specify and responds with the amount of time, in milliseconds, it took for the packet to return. Here is an example of a ping dialog:

 # ping yahoo.com
      PING yahoo.com (204.71.202.160): 56 data bytes
      64 bytes from 204.71.202.160: icmp_seq=0 ttl=246 time=108.0 ms
      64 bytes from 204.71.202.160: icmp_seq=1 ttl=246 time=102.3 ms
      64 bytes from 204.71.202.160: icmp_seq=2 ttl=246 time=102.6 ms
      64 bytes from 204.71.202.160: icmp_seq=3 ttl=246 time=105.5 ms
      64 bytes from 204.71.202.160: icmp_seq=4 ttl=246 time=103.9 ms
      --- yahoo.com ping statistics ---
      5 packets transmitted, 5 packets received, 0% packet loss
      round-trip min/avg/max = 102.3/104.4/108.0 ms
	  

Reading the results from a ping is simple. The only information you really need to take note of is the time=108.0 ms which tells you how many milliseconds it took for the packet to reach the host and return. There isn't any concern unless these numbers are close to 1000 (one second) or an asterisk "*" appears. If the results do exceed 1000, it may mean that there are some problems with your connection to the Internet, the server's connection, or a connection between you and the server. If an asterisk is displayed, there was no response and that also signifies a problem with the connection between you and the server. The other information in the results includes the time to live, the lowest, average and most time it took the packets to complete their trips and the sequence in which the packets were sent.

Traceroute

Traceroute works much like ping in that it sends data packets to a host you specify. However, rather than simply giving you the time it takes for the packets to return, traceroute sends back results for each hop the packet makes. Because of this, traceroute is the perfect tool to see where network problems are occuring. Here is what your average traceroute dialog looks like:

traceroute to yahoo.com (204.71.202.160), 30 hops max, 40 byte packets
      1  151.196.82.1  461.177 ms  765.824 ms  9.107 ms
      2  151.196.149.1  2.773 ms  2.8 ms  2.321 ms
      3  207.68.20.1  5.059 ms  3.735 ms
      4  208.46.126.181  5.785 ms   8.225 ms  7.994 ms
      5  205.171.24.117  7.085 ms  10.513 ms  10.155 ms
      6  205.171.24.38  9.932 ms  6.092 ms  5.844 ms
      7  206.132.150.161  6.138 ms  6.944 ms  6.858 ms
      8  208.178.174.53  6.505 ms  6.19 ms  5.25 ms
      9  208.50.169.86  67.832 ms  69.224 ms  67.641 ms
      10  206.132.254.41  67.499 ms  68.637 ms  67.437 ms
      11  208.178.103.62  67.882 ms  71.674 ms  68.942 ms
      12  204.71.202.160  70.85 ms  73.649 ms  69.539 ms
     

Like ping's results, deciphering traceroute's dialog is easy. Each hop in the route the packet has traveled will be displayed in order with the hostname and/or IP address. Next, the results, in milliseconds, of the three probes that are sent to each hop. The rules for ping results also apply here. Numbers near 1000 and asterisks represent network problems. For example, the following traceroute results shows that there are some problems on the 7-11 hops:

 traceroute to yahoo.com (204.71.202.160), 30 hops max, 40 byte packets
      1  151.196.82.1  461.177 ms  765.824 ms  9.107 ms
      2  151.196.149.1  2.773 ms  2.8 ms  2.321 ms
      3  207.68.20.1  5.059 ms  3.735 ms
      4  208.46.126.181  5.785 ms   8.225 ms  7.994 ms
      5  205.171.24.117  7.085 ms  10.513 ms  10.155 ms
      6  205.171.24.38  9.932 ms  6.092 ms  5.844 ms
      7  206.132.150.161  6.138 ms  6.944 ms  6.858 ms
      8  * * *
      9  * * *
      10  * * *
      11  * * *
      12  * * *
     

If you then performed a WHOIS query against the American Registry for Numbers (ARIN) database on the last IP before the packet loss, you'd see that it's owned by Global Crossing, who happens to provide network-related services including backbone access for many dial-up and website hosting providers. In this case, the network problems would most likely be due to a problem on their network.

On machines running Windows 95, 98, ME or 2000, traceroute can be accessed via a DOS prompt. Select "Run..." from the Start menu and type "command" ("cmd" for Win2K) or click on the MS-DOS Prompt shortcut in your Start Menu. Once you're at the DOS prompt, type "tracert Host-Address*".

For users of MacOS, WhatRoute is available. Please refer to your software's documentation for information on using traceroute.

For those who use *nix systems (BSD, Linux, Solaris etc.), traceroute should have been installed with the OS. Access it by typing "traceroute Host-Address*" at your command line.

*Note: Due to the configuration of our network, you will not be able to ping or traceroute directly to your account. Instead, you will have to ping use the address "router.dmvnoc.com" for these tools.

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