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ARP Process

Description: To answer this question, you do not need a capture file. You just use the provided network topology to analyse step by step on the ARP process when a ping command is issued from PC1 to test the reachability of PC2, which is located on a different network from PC1, as shown in Figure 1. It is assumed that the ARP cache is initially empty at both PCs.
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image.png
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Step 1:

A ping command has been issued from PC1 (IP: 192.168.10.11) to test the reachability of PC2 (IP: 192.168.20.22).
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Step 2:

To reach PC2 from PC1, PC1 relies on its default gateway (R1) to forward the ICMP message to PC2. However, PC1 needs to know the MAC address of its default gateway.
PC1 sends an ARP Broadcast message to find the MAC address of Router R1 (IP: 192.168.10.1).
Table 7
Sender MAC Address
Sender IP Address
Target MAC Address
Target IP Address
1
00:0P:2F:94:36
192.168.10.11
00:00:00:00:00:00
192.168.10.1
There are no rows in this table
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Step 3:

Router R1 receives the ARP request message from PC1 and replies with an ARP Reply message, providing its MAC address to PC1.
Table 8
Sender MAC Address
Sender IP Address
Target MAC Address
Target IP Address
1
00:0D:BC:77:23:8A
192.168.10.1
00:0P:2F:94:36
192.168.10.11
There are no rows in this table
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Step 4:

Upon receiving this ARP reply message from Router R1, PC1 updates its ARP cache with the received MAC address of R1.
Table 9
IP Address
MAC Address
1
192.168.10.1
00:0D:BC:77:23:8A
There are no rows in this table
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Step 5:

The ICMP Echo Request (ping) is sent from PC1 to PC2 via Router R1. However, before forwarding the message to PC2, R1 needs to know the MAC address of PC2. Router R1 sends an ARP Request message to the 192.168.20.0/24 network to find PC2's MAC address.
table
Sender MAC Address
Sender IP Address
Target MAC Address
Target IP Address
1
00:0D:BC:77:23:8B
192.168.20.1
00:00:00:00:00:00
192.168.20.22
There are no rows in this table
⁠
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Step 6:

PC2 receives the ARP request message sent from Router R1 and replies with an ARP Reply message, providing its MAC address to R1.
Table 11
Sender MAC Address
Sender IP Address
Target MAC Address
Target IP Address
1
00:0F:34:7B:55
192.168.20.22
00:0D:BC:77:23:8B
192.168.20.1
There are no rows in this table
⁠
⁠

Step 7:

Upon receiving this ARP reply message from PC2, Router R1 updates its ARP cache with the received MAC address of PC2.
Table 12
IP Address
MAC Address
1
192.168.20.22
00:0F:34:7B:55
There are no rows in this table
⁠
⁠

Step 8:

Finally, Router R1 is able to forward the ICMP Echo Request from PC1 to PC2, and PC2 responds with an ICMP Echo Reply, which is sent back to PC1 via R1.

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