pCOWeb
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D - (destination IP address contained in the subnet)
D1 – search for the MAC address of the site’s server.
Similarly to step B1, to send the message the communications manager must first acquire the MAC address corresponding to the IP; first of all, it
looks up its “table of IP addresses - MAC addresses”; if this is not found, it searches the network by sending an ARP message and waiting for the
response from the server whose IP address is equal to the destination; as soon as the server responds, the PC saves the MAC address in the
table so that this can be used again in the future, without having to send the request each time.
D2 – effectively send the message
Finally, the personal computer sends the message to the server with the MAC address acquired.
E - (destination IP address outside of the subnet: send to the gateway)
In this case, the personal computer will send the message to a special network device called a gateway, whose IP address will have been specified
in the configuration of the PC. The IP address of this device must belong to the same subnet as the personal computer. The message will be sent
to the gateway after the personal computer has acquired the corresponding MAC address, as described in step B1 or D1.
The gateway, if configured by the network administrator to allow communication between the two subnets in question, will forward the message to
the IP destination address; once the response is received, this too will be forwarded to the original sender (the personal computer).
Overall, then, the gateway allows the personal computer to access all other IP addresses outside of its own subnetwork.
Figure B.a - Communication in a network
