The path of a request: DNS, routers and ports

You type an address, press Enter and within a second you have the page. In that second, a worldwide address book of names, several devices that decide where your data passes and a number that indicates which service you are calling have all taken part. When something fails, it fails at one of those points, and knowing which one changes who you notify and what you tell them.

By the end you will be able to explain, step by step, what happens from the moment you type an address until you see the page; tell what a switch does from what a router does, and recognise the ports of the services you will be working with.

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Check how much has stuck. Match each service with its port without looking at the table until you have got it wrong, and pay attention to the line that explains what each one is for: it is what you really need to remember.

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To close the block, go through the whole journey. Advance step by step and, before reading each explanation, say out loud what is going to happen at the node that lights up. Notice at what moment each piece comes in: DNS, the IP address, the router and port 443.

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Takeaways

• DNS translates names into IP addresses; if it fails, it looks as if there is no connection.
• The switch distributes within a network; the router joins networks and chooses the route.
• The port indicates which service on a machine the request is addressed to.
• Only the port that is needed is opened: each open one is a door in plain sight.