ARP in action

January 16, 2019
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In example below we send a ping from host A to host B.

  • Host A doesn’t have an ARP entry for host B.
  • Host B doesn’t have an ARP entry for host A.

  • Step 1. Host A sends an ARP request for host B.
  • Step 2: Host B stores the MAC – and IP address in the ARP table.
  • Step 3: Host B sends an ARP resonse.
  • Step 4: Host A stores the MAC – and IP address in the ARP table.
  • Step 5: Ping process..

Note: Host B stores the MAC – and IP address based on the ARP request. Thus host B will not send an ARP request for host A.

Note: An ARP table can contain multiple IP addresses with the same MAC address. i.e.

Note: An ARP tables can’t contain entries where one IP address has multiple different MAC addresses.

Question: Host with IP address is turned off 192.168.2.247. Another host is turned on and gets IP address 192.168.2.247. What happens?

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Host A sends packets to host B with 192.167.2.247. However host A uses wrong MAC address. No host responds. After a while, host A sends an ARP request with the wrong MAC address. No host responds. Than host A sends an ARP request with a broadcast MAC address. Host B sends an ARP response. Now we get a ping response.