ARP mechanism

  1. Computers Matterhorn and Washington are in an office
    1. connected to each other on the office local area network by 
      1. Ethernet cables and 
      2. network switches, 
    2. with no intervening gateways or routers
  2. Matterhorn wants to send a packet to Washington
    1. Through other means, it determines that Washington's IP address is 192.168.0.55. 
    2. In order to send the message, it also needs to know Washington's MAC address.
      1. First, Matterhorn uses a cached ARP table to look up 192.168.0.55 for any existing records of Washington's MAC address (00:eb:24:b2:05:ac). 
        1. If the MAC address is found,
          1. it sends the IP packet on the link layer to address 00:eb:24:b2:05:ac via the local network cabling. 
        2. If the cache did not produce a result for 192.168.0.55, 
          1. Matterhorn has to send a broadcast ARP message (destination FF:FF:FF:FF:FF:FF) requesting an answer for 192.168.0.55. 
          2. Washington responds with its MAC address (00:eb:24:b2:05:ac). 
            1. Washington may insert an entry for Matterhorn into its own ARP table for future use.
          3. The response information is cached in Matterhorn's ARP table and 
  3. the message can now be sent.

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