Data is sent and received every second of every day. Every day, your company’s network processes billions of data packets. Although you received many packets to read this article, the vast majority of people don’t know how it works.
It is difficult to understand what happens behind the scenes to ensure that data reaches the right device. It’s crucial that the right device receives the right data, with an estimated 4.66 billion internet users.
Let’s take a look at a story to understand how data is delivered.
This Story explains Data Delivery
Janet must send George a message
Janet works at a large real-estate firm. Janet has a list with properties for sale that she would like her firm to purchase. She must get the list to the right partner so that the paperwork can be prepared.
She knows George’s name but doesn’t know where he is. Is he in the same building as her or in one of the remote offices in town?
He is not listed in her building directory. She pulls up her most recent contact list but doesn’t see George’s name. She hasn’t spoken to George in a while, so she doesn’t have his address information. She could have the letter sent directly to George if she had his information in her files.
Instead, she sends it to shipping and receiving and says it should go to George.
Janet’s Shipping and Receiving Department locates George
The shipping and receiving department then searches for George’s location in a larger database. It is found that George is in a remote office in another town. The resources required to deliver the document to George are not available to shipping and receiving. This would be prohibitively expensive with as many branches as they have.
Instead, they send the letter to the postoffice with the correct street address information for George’s house and his office number.
The Post Office Transmits the Message
The post office then uses its resources to determine the best route to deliver the letter to George’s shipping and receiving offices. The post office doesn’t know (or care) where George is located in the building, even though it has the suite number on the package.
Instead, the postal worker gives the envelope to the shipping or receiving clerk.
George’s Shipping and Receiving Department Delivers Your Message
The clerk then observes the suite number on each envelope and has it delivered to George’s office. George can now look at this list to determine which properties make the most sense to buy.
How this Story Translates into Data Delivery
Janet is the sending host. George’s name is the destination host. He has a MAC address and his location. Your host also has a list with local network information, called an ARP cache and Host Table. Jane uses this information to create her building directory.
If your host is able to find the relevant information in the local data, it will use the switch to send traffic to the device in its local network. Janet’s host cannot find the relevant information in the local ARP cache or host route table so it will have to send the data packet directly to Janet.
In my story, the receiving and shipping departments fulfill two of these functions.
First, we must convert the MAC address to an IP address. The ARP accomplishes this by sending a request packet. The device responding to the request packet uses its MAC address.
The data is sent to default gateway if the destination host (e.g. George) is not present in the building. This is also represented by the shipping or receiving department. The default gateway may have its own route table, which may include information about the outside network, such as the internet.
The internet is my analogy.