Question

So, now you know that all machines that are on a network need to have an IP address. I live in Denver, Colorado, and one of my best friends, Ryan, lives in Albuquerque, New Mexico. When I send him a message, it does not travel from my house through the wires directly to his house. It goes through “hops” (and not the beer kind, unfortunately for him). These hops are the routers between us.

Tracert is a cool diagnostic utility. It will determine the route the message takes from Denver to Albuquerque by using ICMP echo packets sent to the destination. You've seen ICMP in action before—with the ping command.

ICMP is one of the Internet's original protocols used by network devices to send operational information or error messages. ICMP is not usually used to send data between computers, with the exception of ping and traceroute . It is used to report errors in the processing of datagrams.

Each router along the path subtracts the packets TTL value by 1 and forwards the packet, giving you the time and the intermediate routers between you and the destination. Tracert will print the trace of the packet's travels.

Why is this an important part of your toolkit? This is how you find out where a packet gets stopped or blocked on the enterprise network. There may be a router with a configuration issue. Firewalls can be configured to filter packets. Perhaps your website is responding slowly. If packets are being dropped, this will be displayed in the tracert as an asterisk.

This is a good tool when you have many paths that lead to the same destination but several intermediary routers are involved.

One caveat before Lab 1.4 : As I mentioned previously, most of my strengths lie in Windows machines. If you are on a Linux or Mac/Unix‐type operating system (OS), then you will want to use the tool traceroute . The commands tracert and traceroute are basically the same thing. The difference lies in which OS you are troubleshooting. If you want to get supremely technical, in Linux the command sends a UDP packet. In Windows, it sends an ICMP echo request.

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LAB 1.4 : TRACERT

1. Open a command prompt or a terminal window.
2. At the command prompt, type tracert 8.8.8.8 and press Enter.

In Figure 1.7 , you can see the hops my machine takes to reach that public Google DNS server. How many hops does yours take?

Figure 1.7 : Using tracert , counting hops

3. Now try tracert –d 8.8.4.4 .

This is another public Google DNS server, but now tracert will not try to resolve DNS while counting the hops.

4. For fun, try tracert 127.0.0.1 . Why is it only one hop?

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