The document provides an overview of the traceroute command, a network diagnostic tool for mapping the path packets take to their destination. It explains how traceroute operates using the Time to Live (TTL) field in IP packets, and includes an example output showing the sequence of routers and their response times. The document concludes with a description of how traceroute incrementally adjusts TTL to receive responses from each router until it reaches the target machine.

1. Secondary School of Batalha Pedro Perfeito May 2009

2. Index 1. Introdution 2. Output of a traceroute 3. How a traceroute works (1) 4. How a traceroute works (2)

3. Introdution Traceroute is a network diagnostic tool found on most operating systems, which is used for determining which path a packet has taken. The traceroute command can be used to draw up a map of the routers found between a source machine and a target machine. The traceroute command is different on each operating system. The traceroute command is: tracert name.of.the.machine H

4. Output of a traceroute A traceroute's output describes the names and IP addresses of the chain of routers, each preceded by a sequential number and minimum, average, and maximum response time. A rastrear a rota para cisco.netacad.net [128.107.229.50] H Tracing a route to cisco.netacad.net [128.107.229.50] over a maximum of 30 hops: 1 * * * O pedido excedeu o tempo. 2 127 ms 129 ms 139 ms lis1-br1-gi6-2.cprm.net [195.8.10.201] 3 118 ms 139 ms 149 ms lis1-cr1-po.cprm.net [195.8.0.221] 4 238 ms 259 ms 269 ms was1-cr1-ge62.telecom.pt [206.223.115.82] 5 248 ms 249 ms 249 ms ex2-g8-0s1.eqabva.sbcglobal.net [206.223.115.79] 6 318 ms 328 ms 320 ms ded4-g1-3-0.sntc01.pbi.net [151.164.41.161] 7 299 ms 318 ms 319 ms Cisco-Systems-1152786.cust-rtr.pacbell.net [64.161.0.62] 8 298 ms 319 ms 320 ms sjc5-dmzbb-gw1-gig1-47.cisco.com [128.107.224.105] 9 298 ms 319 ms 310 ms sjc12-dmzdc-gw2-gig1-1.cisco.com [128.107.224.18] 10 299 ms 319 ms 319 ms cna-prod-nv.cisco.com [128.107.229.50] Route traced.

5. How a traceroute works (1) Traceroute works thanks to the TTL field in IP packets. Each IP packet has a time to live field (TTL) which is reduced each time it goes through a router When this field reaches zero, the router determines that the packet has been going around in circles, terminates this packet and sends an ICMP notification to the sender. H

6. How a traceroute works (2) For this reason, traceroute sends packets to an unprivileged UDP port which is believed to be unused (port 33434 by default) with a TTL set to 1. The first router encountered will delete the packet and send an ICMP packet which includes the IP address of the router as well as the loop delay. Traceroute then increases the TTL field by 1 at a time, so as to obtain a reply from each router on the pathway, until it gets the reply "ICMP port unreachable" from the target machine. H

7. That´s all… thanks for watching! H