Traceroute is an application that works in a similar fashion as PING. Traceroute uses ICMP ECHO_REQUESTs to determine the path that packets take to get to a destination host. Traceroute does this by first sending an ICMP ECHO_REQUEST to the destination host with a time to live (TTL) of 1. The first device along the path receives the packet and decrements the TTL counter. The TTL is not zero, so the router sends back a HOST_UNREACHABLE response to the originating host. Traceroute then sends another ICMP_REQUEST with the TTL set to 2. The packet passes through the first router (which decrements the TTL to 1), and when the second router in the path receives it, the TTL is decremented by 1. The second router sees the TTL is 0 and ...

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