COMP 2322 Lab 5 IP Steven Lee March

COMP 2322 Lab 5 IP Steven Lee March 18, 2016

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IP • Internet Protocol • Network layer protocol 3

Traceroute • A network diagnostic tool for displaying the route (path) and packet delays across an IP network • Named “tracert” on Windows • Named “traceroute” on Mac OS 4

Practice 1 • Start capturing packets • On Windows, input command “tracert 8. 8” On Mac OS, input command “traceroute 8. 8” • Stop capturing packets • Enter “icmp” into the display filter to show only icmp packets 5

Practice 1 Question 1 (8 marks) a) How many unique IP addresses do the ICMP echo reply packets (“reply packets”) come from? b) How does the time to live (TTL) change for each subsequent set of request packets? c) Why are all reply packets, except those of the last set, being ICMP TTL-exceeded messages? d) How does traceroute trace the path to a certain host? 6

Practice 2 • Start capturing packets • On Windows, input command “ping -n 1 -l 2000 www. example. com” On Mac OS, input command “ping -c 1 -s 2000 www. example. com” • Stop capturing packets • To display IP packet fragments • Right-click on any IP layer → Protocol Preferences → Uncheck Reassemble fragmented IPv 4 datagrams • Use “ip. addr==<IP address of www. example. com>” as the display filter 7

Practice 2 Question 2 (12 marks) a) How many IP datagrams is the ICMP echo request packet fragmented into? Look at the first fragment. b) What information in the IP header indicates that it is fragmented? c) What information in the IP header indicates that it is the first fragment? d) How long is this fragment? Look at the second fragment. e) What information in the IP header of the second fragment indicates that it is not the first fragment? f) Are there more fragments? How can you tell? 8

Practice 3 • To check the current MTU: On Windows, input command “netsh interface ipv 4 show subinterfaces” On Mac OS, input command “networksetup -get. MTU en 0” Question 3 (2 marks) What is the current MTU? 9

Practice 4 • To check the routing table, input command “netstat -rn” Question 4 (4 marks) a. Which entry in the routing table matches an IP packet with a destination address of 158. 132. 82. 94? b. There are multiple entries in the routing table which match an IP packet with a destination address of 255, which of them will actually be used to forward the packet? 10