Zhou, HuanXian (ID: 0225418) HW8 EE136 Instructor: Kang Xi 1. Using command traceroute (tracert in windows) can find the path to a host. Briefly explain how traceroute is designed (hint, which IP header field is controlled and how to get the feedback). Traceroute transmits packets with small TTL (Time To Live) values. TTL 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, 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; etc. 2.
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This note was uploaded on 11/02/2010 for the course EE 136 taught by Professor Kang xi during the Spring '10 term at NYU Poly.