Describe how the ICMP route redirect works using the output you saved. Include only relevant data from your saved output to support your explanations.

Question

What will be an ideal response?

Answer 1

No. Time Source Destination Protocol Info
5 8.687724 10.0.2.10 10.0.3.10 ICMP Echo (ping) request
6 8.688619 10.0.2.1 10.0.2.10 ICMP Redirect
11 9.691468 10.0.2.10 10.0.3.10 ICMP Echo (ping) request
12 9.692372 10.0.2.1 10.0.2.10 ICMP Redirect
13 9.692575 10.0.2.10 10.0.3.10 ICMP Echo (ping) request
15 10.703191 10.0.2.10 10.0.3.10 ICMP Echo (ping) request
17 11.723095 10.0.2.10 10.0.3.10 ICMP Echo (ping) request
18 12.743137 10.0.2.10 10.0.3.10 ICMP Echo (ping) request

ICMP Redirect message are sent in the following manner:
– PC2 sends ARP request looking for MAC address of Router1 (10.0.2.1).
– Router1 sends ARP reply to PC2 with MAC address of eth1.
– PC2 sends ICMP request to Router1.
– Router1 sends ICMP Redirect message to PC2, telling PC2 the correct gateway should be
10.0.2.2, eth1 of Router2.
– PC2 now sends ARP request looking for MAC address of Router2 (10.0.2.2).
– Router1 also forwards the original ICMP request (Frame 3) from PC2 to Router2.
– Router2 sends ARP reply for Frame 5 to PC2 with MAC address of eth1.
– Router2 sends ICMP reply for Frame 6 back to PC2.
– PC2 now correctly sends ICMP request to Router2.
– Router2 sends ICMP reply to PC2.
ICMP route redirect message works by adding correct route(s) to the routing cache of a machine (for
a certain destination). When this machine is to send packet to the same destination again, it will first check the routing cache to see if there is a match before jumping into the routing table. If the correct route presents in the cache, the machine can send the packets through a correct gateway. When the entry in the routing cache expires, packets will be sent wrongly again and ICMP redirect message will be generated so the correct route will be add to the cache again.