PC2 10.0.2.10 / 24 PC3 10.0.3.10 / 24 PC4 10.0.4.10 / 24 Table 3.2 IP addresses for Part 4 Exercise 4. Observing forwarding loops Set up the network topology as shown in Figure 3.2 and configure the interfaces as shown in Table 3.2. Set up all the PC routing tables to allow communication between all 4 PCs. Configure the routing tables of Router2, Router3 and Router4, so that an ICMP Echo Request message generated by a ping from PC4 to PC1 creates an infinite loop. Issue a to verify that a loop exists: traceroute PC4% traceroute 10.0.1.10 You should observe that the traced path is a loop. Start Wireshark sessions on PC2, PC3, and PC4. Issue a ping from PC4 to PC1. You should observe the same ICMP Echo Request message looping in Wireshark. Save the routing tables of Router2, Router3 and Router4. Count the number of times you see the ICMP Echo Request message, as captured by Wireshark on PC4. Save at least two of these ICMP Echo Request messages. Lab Questions Are the two packets that you saved identical? If not, what is different? Why does the ICMP Echo Request packet not loop forever in the network? PART 5. NETWORK PREFIXES and ROUTING In this exercise you study how the network prefixes (netmasks) play a role when hosts determine if a datagram can be directly delivered or if it must be sent to a router. This part uses the network setup shown in Figure 3.3. The network includes one router, four hosts and two hubs. The IP addresses of all devices are given in Table 3.4. Here, each host has only a default route. In other words, the routing table at a host only knows about the directly connected networks and the default gateway.
PC2 10.0.2.10 / 24 PC3 10.0.3.10 / 24 PC4 10.0.4.10 / 24 Table 3.2 IP addresses for Part 4 Exercise 4. Observing forwarding loops Set up the network topology as shown in Figure 3.2 and configure the interfaces as shown in Table 3.2. Set up all the PC routing tables to allow communication between all 4 PCs. Configure the routing tables of Router2, Router3 and Router4, so that an ICMP Echo Request message generated by a ping from PC4 to PC1 creates an infinite loop. Issue a traceroute to verify that a loop exists: PC4% traceroute 10.0.1.10 You should observe that the traced path is a loop. Start Wireshark sessions on PC2, PC3, and PC4. Issue a ping from PC4 to PC1. You should observe the same ICMP Echo Request message looping in Wireshark. Save the routing tables of Router2, Router3 and Router4. Count the number of times you see the ICMP Echo Request message, as captured by Wireshark on PC4. Save at least two of these ICMP Echo Request messages. Lab Questions Are the two packets that you saved identical? If not, what is different? Why does the ICMP Echo Request packet not loop forever in the network? PART 5. NETWORK PREFIXES and ROUTING In this exercise you study how the network prefixes (netmasks) play a role when hosts determine if a datagram can be directly delivered or if it must be sent to a router. This part uses the network setup shown in Figure 3.3. The network includes one router, four hosts and two hubs. The IP addresses of all devices are given in Table 3.4. Here, each host has only a default route. In other words, the routing table at a host only knows about the directly connected networks and the default gateway.