My Netwok Dictionary

Introduction to Traceroute

Traceroute is a tool for diagnosing networks, present on most operating systems, to determine the path followed by a package. The traceroute command allows to draw a map of the routers between a source machine and target machine. The traceroute command differs between operating systems.

Under the systems UNIX / Linux , the traceroute command is as follows:
traceroute name.of.machine

Under the systems Windows , the traceroute command is as follows:
tracert name.of.machine

Output of traceroute

The traceroute command provides output describing the names and IP addresses of successive routers, preceded by a serial number and the minimum response time, average and maximum:

Tracing route to www.mynetworkdictionary.com [205.234.219.179] over a maximum of 30 hops:
1 33 ms 32 ms 33 ms Raspail-2-81-57-234-254.fbx.proxad.net [81.57. 234 254]
2 33 ms 33 ms 33 ms vlq-6k-2-a5.routers.proxad.net [213.228.4.254]
3 33 ms 33 ms 33 ms vlq-6k-2-v802.intf.routers.proxad.net [ 212.27.50.46]
4 33 ms 33 ms 33 ms th1-6k-2-v806.intf.routers.proxad.net [212.27.50.41]
5 32 ms 34 ms 34 ms CBV-6k-2-v802.intf.routers. proxad.net [212.27.50.34]
6 34 ms 32 ms 33 ms ldc-6k-1-a0.routers.proxad.net [213.228.15.67]
7 35 ms 35 ms 35 ms cogent.FreeIX.net [213.228.3.187]
8 36 ms 36 ms 35 ms NeufTelecom.demarc.cogentco.com [130.117.16.22]
9 36 ms 36 ms 36 ms V3994.c1cbv.gaoland.net [212.94.162.209]
10 34 ms 34 ms 35 ms V4080.core3.cbv . gaoland.net [212.94.161.129]
11 36 ms 35 ms 37 ms 212.94.164.210 12 36 ms 36 ms 36 ms nestor.commentcamarche.org [163.5.255.85]
Route determined.

How Traceroute

Traceroute supports its operation on the TTL field of IP packets. Indeed, each IP packet has a field life TTL (Time to Live) decremented each time a router. When this field reaches zero, the router, whereas the package in a loop, destroys the packet and sends an ICMP notification to the sender.

Thus, traceroute sends packets to a UDP port unprivileged deemed not used (default port 33434) with a TTL equal to 1. The first router encountered will remove the package and send an ICMP giving including the IP address of the router and the propagation time loop. Traceroute will increment sequentially and field life in order to obtain a response from each router along the path until you get a reply “ICMP port unreachable” from the target machine.