As a result of this behavior, a datagram with a TTL of 1 (sent by the host executing traceroute) will cause the router one hop away from the sender to send an ICMP TTL-exceeded message back to the sender the datagram sent with a TTL of 2 will cause the router two hops References to figures and sections are for the 7 edition of our text, Computer Networks, A Top-down Approach, 74 ed.
If the TTL reaches 0, the router returns an ICMP message (type 11 – TTL-exceeded) to the sending host. Recall that a router must decrement the TTL in each received datagram by 1 (actually, RFC 791 says that the router must decrement the TTL by at least one). Recall that 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. Capturing packets from an execution of traceroute 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. You'll also want to read Section 4.3 in the text and probably also have RFC 791 on hand as well, for a discussion of the IP protocol. Before beginning this lab, you'll probably want to review sections 1.4.3 in the text' and section 3.4 of RFC 2151 to update yourself on the operation of the traceroute program. We'll investigate the various fields in the IP datagram, and study IP fragmentation in detail. We'll do so by analyzing a trace of IP datagrams sent and received by an execution of the traceroute program (the traceroute program itself is explored in more detail in the Wireshark ICMP lab). Ross, All Rights Reserved In this lab, we'll investigate the IP protocol, focusing on the IP datagram. " Chinese proverb © 2005-2016, Kurose and K.W. Ross A TOP-DOWN APPROACH LES COMO KLIROS-ROSS "Tell me and I forget. Transcribed image text: Wireshark Lab: IP v7.0 Computer Networking Supplement to Computer Networking: A Top-Down Approach, 7th ed., J.F.
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