Answer to Question #262733 in Computer Networks for H A

Question

 Explain how traceroute works. Include a traceroute to a host at least 8 hops away?

Answer 1

Traceroute transmits packets with small TTL values. Recall that the TTL (Time To Live) is an IP header field that is designed to prevent packets from running in loops. Every router that handles a packet subtracts one from the packet's TTL. If the TTL reaches zero, the packet has expired and is discarded. Traceroute depends on the common router practice of sending an ICMP Time Exceeded message, documented in RFC 792, back to the sender when this occurs. By using small TTL values which quickly expire, traceroute causes routers along a packet's normal delivery path to generate these ICMP messages which identify the router. A TTL value of one should produce a message from the first router; a TTL value of two generates a message from the second; etctraceroute iitkgp.ernet.in

traceroute: Warning: iitkgp.ernet.in has multiple addresses; using 202.141.127.2traceroute to iitkgp.ernet.in (202.141.127.2), 30 hops max, 38 byte packets

 1 csworld43 (128.111.43.1) 14.072 ms 1.448 ms 1.302 ms

 2 128.111.235.1 (128.111.235.1) 2.156 ms 4.469 ms 1.912 ms

 3 556-NOC-556-c.noc.ucsb.edu (128.111.4.65) 1.479 ms 3.376 ms 0.913 ms

 4 574-c.noc.ucsb.edu (128.111.2.19) 3.636 ms 4.275 ms 1.545 ms

 5 gsr-ngb.commserv.ucsb.edu (128.111.252.153) 1.345 ms 4.358 ms 1.879 ms

 6 border1-g-1-0-0.commserv.ucsb.edu (128.111.252.149) 1.770 ms 4.407 ms 2.158 ms

 7 teanet-qanh-far.commserv.ucsb.edu (128.111.252.10) 13.318 ms 4.928 ms 5.578 ms

 8 bur-edge-01.inet.qwest.net (65.119.29.93) 8.644 ms 6.570 ms 6.764 ms