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THE INTERNET, PING, AND TRACEROUTE | Forum

Topic location: Forum home » General » There.com
Ayman Admin
Ayman Aug 11
THE INTERNET, PING, AND TRACEROUTE


The internet is comprised mostly of "servers" (computers that serve a function for you, like a computer running a web server, or a mail server, or a There server!) and "routers" which are specialized computers that simply send "packets" from place to place. A packet is a small piece of data with information about where it's coming from and where it's going to. There are several different types of packets, and for right now you need to know about tcp/ip and icmp packets. Most of the traffic for the things you do on the net is sent in tcp or udp packets, which are part of "ip".� For the sake of simplicity right now, we'll just talk about tcp/ip, which is what is mostly being used when you send and receive data over the net. The other kind of packet we're going to talk about is an "icmp" packet. This type of packet is used when you "ping" or "traceroute".

When you are having a bad experience in There, sometimes it is because some of the tcp/ip (or udp) packets that are being sent between the servers and your computer are being "dropped" or "lost". And sometimes it is because it is taking so long for them to get between your computer and the servers that your There client gets unhappy or things happen very slowly. Using There is very different from web-browsing, where a slow or lossy connection doesn't usually cause you much pain unless you are downloading big files or streaming media. Using There requires a nice stable connection between your computer and the There services, with low latency, or round-trip time for the packets, and low packet loss.

The tool called "ping" will send packets to another computer, and show you the latency, or round-trip time of packets between your computer and the other computer. This can help show you when the connection is slow. It will also show when packets are dropped or lost. The tool called "traceroute" (the command is "tracert" on windows), will show you the _path_ that packets take to get from your computer to their destination.

It is important to understand that routers handle icmp packets very differently from the way they handle tcp/ip (or udp) packets. icmp packets are generally considered very much less important. A busy router may drop icmp packets when it is not dropping tcp/ip packets at all. Also, some routers do not like to respond to icmp packets at all, and will not show up in a traceroute even though they exist in the path.

Here is an example of a "ping" from a windows machine to www.there.com:

C:> ping www.there.com

Pinging www.there.com [64.125.216.193] with 32 bytes of data:

Reply from 64.125.216.193: bytes=32 time=21ms TTL=249
Reply from 64.125.216.193: bytes=32 time=8ms TTL=249
Reply from 64.125.216.193: bytes=32 time=25ms TTL=249
Reply from 64.125.216.193: bytes=32 time=13ms TTL=249

Ping statistics for 64.125.216.193:
��� Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
��� Minimum = 8ms, Maximum = 25ms, Average = 16ms
C:>

Note that you may get a different IP address for www.there.com, as we have multiple servers hosting www.there.com. The important things to note here are the average round trip time, and the packet loss. I see a nice 0% loss, and a very nice 16ms average round trip time. Latency up to 100ms is not at all abnormal on the internet. And you'll often see latency in the 200-300ms range and it doesn't necessarily mean anything is wrong. You might be on a small ISP or network provider, and have more hops or routers to go through. Your ISP (or some provider along the way) might have a very busy router or a low bandwidth connection to the next network provider along the way. You probably shouldn't worry about your There experience unless the latency gets above 500ms.

Now here's an example of a traceroute:

C:>tracert www.there.com

Tracing route to www.there.com [64.125.216.193]
over a maximum of 30 hops:

� 1���� 1 ms���� 1 ms���� 1 ms� firewall-int.thereinc.com [10.10.1.1]
� 2���� 6 ms���� 3 ms���� 3 ms� 216.200.151.161.there.com [216.200.151.161]
� 3��� 11 ms��� 16 ms��� 17 ms� 64.124.60.10.there.com [64.124.60.10]
� 4��� 28 ms��� 13 ms��� 22 ms� 64.124.60.62.available.above.net [64.124.60.62]
� 5��� 20 ms��� 20 ms��� 29 ms� 262.ge-4-3-0.er10b.sjc2.us.above.net [64.124.33.83]
� 6��� 13 ms��� 34 ms���� 8 ms� 64.124.33.93.available.above.net [64.124.33.93]
� 7��� 21 ms��� 16 ms��� 26 ms� www.there.com [64.125.216.193]

Trace complete.

C:>

You see the round trip time of each packet in milliseconds on the left, and the name and/or IP address of the server/router on the right. If, instead of a number of ms, the tracert output shows a *, that's a packet that was dropped or lost.

Remember that I mentioned that icmp packets are sometimes dropped when tcp/ip packets are not. So don't panic if you see an occasional * here or there! That's normal. What isn't normal is when a percentage of packets is dropped over a long period of time. So it's important to not just ping or traceroute for 30 seconds, but instead to look over a longer period of time.

It is VERY IMPORTANT to understand that while ping and traceroute are very valuable tools for helping to find and understand problems with internet connectivity, they can be mis-leading. Sometimes they seem to indicate problems when there are not really problems. Sometimes they seem to indicate no problems when there really are problems. This article gives a good explanation of why this is the case:

http://homepage.ntlworld.com/robin.d.h.walker/cmtips/traceroute.html

I've just given you a very basic understanding of ping and traceroute. If you'd like a more in-depth discussi
on about how the internet works and about these tools, there are several on the net and in various books. Her
e's one web page I found which I think is a pretty good overview:

http://cyber.law.harvard.edu/digitaldemocracy/internetarchitecture.html

Thanks,
--jessica
There Operations

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