Overview
Tracert (also called traceroute) will trace the route that packets take from one destination to another. The tool here will trace the route that a packet takes from our web server to the destination that you enter (either a host name, such as www.example.com, or an IP address). The results display a list of routers traversed (the path taken) for a packet from our web server to reach a particular destination on the network.
A timeout can be set if your internet connection is very slow.
For IPv6 tracerts, enter the IPv6 address or the hostname preceded by a colon (':host.example.com').
How to read Traceroute results
The results of a tracert normally will include at least 4 pieces of information for each hop -- the hop number, the time it takes for the packets to get to that hop and back, the IP address of the hop, and the hostname corresponding to the IP address (if any).
Most tracert programs send out 3 packets for each hop, in case any packets are lost, and to get an idea of whether or not the time varies for any specific hop.
Here is a sample tracert:
Tracing route to i.root-servers.net [192.36.148.17] over a maximum of 30 hops:
1 <1 ms <1 ms <1 ms c-vl102-d1.acc.dca2.hopone.net [66.36.240.2]
2 <1 ms <1 ms <1 ms ge4-0.core2.dca2.hopone.net [66.36.224.243]
3 1 ms 1 ms 1 ms ge2-0-241.core1.iad1.hopone.net [66.36.224.34]
4 1 ms 1 ms 1 ms equinix-ashburn.woodynet.net [206.223.115.111]
5 2 ms 2 ms 2 ms i.root-servers.net [192.36.148.17] Trace complete.
The top line of the tracert lets us know what computer the tracert program is tracing the route to. In this case, we are tracing the route to i.root-servers.net (which has an IP address of 192.36.148.17). It also lets us know that it will stop if it reaches a maximum of 30 hops.
The next line shows us that for hop number 1, the 3 packets each had a RTT (Round Trip Time, the time that it takes for the packet to get there and back) of less than 1 ms (1 ms is a 1/1000th of a second, so 100ms is 1/10 second). It then shows us that the router on the first hop is at the IP address 66.36.240.2 with a name of c-vl102-d1.acc.dca2.hopone.net.
The second hop, ge4-0.core2.dca2.hopone.net [66.36.224.243], also had a RTT of less than 1ms. The third hop, ge2-0-241.core1.iad1.hopone.net [66.36.224.34], had a RTT of 1ms. The fourth hop, equinix-ashburn.woodynet.net [206.223.115.111], also had a RTT of 1ms. The fifth hop, i.root-servers.net [192.36.148.17], is the destination. It had a RTT of 2ms.
What did we learn from this tracert? We learned that there are only 5 hops from the source (in this case, the www.DNSstuff.com server) and the destination (i.root-servers.net), and that it takes packets 2ms to get from one computer to the other. This is one of the shortest and fastest tracerts that you will normally see (since I picked a location close to the www.DNSstuff.com site). Normally, there will be 10-20 hops, and the times between hops can give many clues as to whether or not there are network problems.
One other piece of information we can get here is where the packets went. The first 3 hops include "dca2" and "iad1". Both "dca" and "iad" are codes for Washington, DC ("iad" is the airport code for an airport in Washington, DC; many tracert packets have airport codes in them). The fourth hop mentions "ashburn", which is Ashburn, VA. The last hop doesn't have a clue as to where it is located, but usually the last hop is located at the same place as the previous hop. So the packet likely went from Washington, DC to Ashburn, VA, which is a very short trip (which is part of why the RTTs are so low).
Who or what determines how many hops a domain must go through before it reaches its destination?
It depends on several factors. It depends on how many organizations handle the packets between the source and the destination, and how many routes the packets take within each organization.
For example, a tracert from http://www.DNSstuff.com to http://www.google.com goes directly from our bandwidth provider (HopOne Internet) to Google, so there are only 2 organizations involved (usually there are more than two, however). Even though there are only 2 organizations involved, the packets go through 7 hops.
Why 7 hops? That's because the packets go from the datacenter that http://www.DNSstuff.com is located in (in Washington, DC) to another HopOne datacenter (also in Washington, DC), then to an exchange point in Virginia (where lots of Internet providers connect with each other) where the packets get handed off to Google's network. The packets then take a couple more hops on the Google network (unfortunately, I can't say exactly where they go or why, as Google doesn't provide enough information about it, likely for security reasons).
Often you'll see a packet reach a major backbone (such as AlterNet), and go through several hops through different cities (such as New York to Washington, DC to San Jose, California). This happens when there is no direct route between one city and another, so the packets get routed through a third city.