Use the captured data to explain the outcome of the exercise. Use the data to explain how Proxy ARP allowed PC4 to communicate with PC1. Include only relevant data from your saved output.
What will be an ideal response?
When PC4 attempted to ping PC1, it sent out an ARP request (Frame 2) for the MAC address
of PC1. Because PC4 is directly connected to Router1 and Router1 works as proxy ARP, Router1
sent out a Proxy ARP reply (Frame 3) telling PC4 that PC1 can be reached via the MAC address of
Router1’s eth1.
PC4 : No. Time Source Destination Protocol Info
2 3.150617 00:04:75:ac:88:5d ff:ff:ff:ff:ff:ff ARP Who has 10.0.1.11? Tell 10.0.3.41
3 3.152743 00:10:7b:81:8c:8f 00:04:75:ac:88:5d ARP 10.0.1.11 is at 00:10:7b:81:8c:8f
4 3.152757 10.0.3.41 10.0.1.11 ICMP Echo (ping) request
5 3.158078 10.0.1.11 10.0.3.41 ICMP Echo (ping) reply
6 4.162768 10.0.3.41 10.0.1.11 ICMP Echo (ping) request
7 4.163893 10.0.1.11 10.0.3.41 ICMP Echo (ping) reply
After pinging from PC4 to PC1, the MAC address of Router1’s eth1 is added to PC4’s ARP table,
but showing the corresponding IP address of PC1.
From this point on, ICMP request messages (Frame 4 & 6) are sent from PC4, with destination IP
address of PC1 and destination MAC address (Ethernet II) of Router1’s eth1.
Also PC1 can reply back to those request packets.
PC1: No. Time Source Destination Protocol Info
1 0.000000 00:04:75:ad:04:cd ff:ff:ff:ff:ff:ff ARP Who has 10.0.1.11? Tell 10.0.1.21
2 0.000021 00:04:75:ac:87:22 00:04:75:ad:04:cd ARP 10.0.1.11 is at 00:04:75:ac:87:22
3 0.000310 10.0.3.41 10.0.1.11 ICMP Echo (ping) request
4 0.000330 10.0.1.11 10.0.3.41 ICMP Echo (ping) reply
5 1.010036 10.0.3.41 10.0.1.11 ICMP Echo (ping) request
6 1.010063 10.0.1.11 10.0.3.41 ICMP Echo (ping) reply
7 4.992466 00:04:75:ac:87:22 00:04:75:ad:04:cd ARP Who has 10.0.1.21? Tell 10.0.1.11
8 4.992667 00:04:75:ad:04:cd 00:04:75:ac:87:22 ARP 10.0.1.21 is at 00:04:75:ad:04:cd
The reason this situation works is that Router1 has a routing table entry to reach the subnet of PC1 and works as a proxy ARP agent. When Router1 receives an ARP request for PC1 and realize the destination is reachable from itself, it in turn sends out its own ARP request to PC1 to obtain its MAC address. After Router1 receives the ARP reply from PC1, it then passes on the MAC address of PC1 back to PC4, thus the term “proxy”.
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