If the TTL reaches 0, the router returns an ICMP message (type 11 – TTL-exceeded) to the sending host. Router must decrement the TTL by at least one). Recall that a router mustĭecrement the TTL in each received datagram by 1 (actually, RFC 791 says that the Traceroute operates by first sending one or more datagrams with the time-to-live (TTL) field in the IP header set to 1 it then sends a series of one or more datagrams towards the same destination with a TTL value of 2 it then sends a series of datagrams towards the same destination with a TTL value of 3 and so on. In order to generate a trace of IP datagrams for this lab, we’ll use the traceroute program to send datagrams of different sizes towards some destination, X. It is important that you carefully read the instructions such that you provide answers in the desired format(s).Ĭapturing packets from an execution of traceroute In this assignment, you will be asked to answer and/or discuss a number of questions. You’ll also want to read Section 4.4 in the book, and probably also have RFC 791 on hand as well, for a discussion of the IP protocol.
We’ll investigate the various fields in the IP datagram, and study IP fragmentation in detail.īefore beginning this lab, you’ll probably want to review sections 1.4.3 in the course text book and section 3.4 of RFC 2151 to update yourself on the operation of the traceroute program. We’ll do so by analyzing a trace of IP datagrams sent and received by an execution of the traceroute program. In this lab, we’ll investigate the IP protocol, focusing on the IP datagram.
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