Networking Basics: Part 1

ARP (Address Resolution Protocol)

The ARP is used to associate the network layer address, IP address, with the data link layer, MAC address. ARP is needed because the computer sending the packets will not know the destination MAC address, so it uses ARP to find the destination MAC address. MAC addresses are fixed and they are encoded into the Network Interface Card. The process can be explained clearly in steps (The computer that is sending the packets is called: Computer A and the computer receiving the packets is called Computer B) :

  • Step 1: An ARP request is sent, this request is a broadcast to all devices on the network. This request is for the computer B to send a response.
  • Step 2: All devices on the network that don’t have the destination IP address will ignore the request.
  • Step 3: The device with the correct destination IP address (Computer B) will save Computer A IP address and associated MAC address in the ARP table, so know that Computer B knows how to reach computer B .
  • Step 4: Now the Computer B will send an ARP reply to Computer A.
  • Step 5: Computer A will now will save Computer B’s IP address and associated MAC address in its ARP table.
  • Step 6: Now Computer A can send packets with the correct destination MAC address of Computer B.
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