Understanding IP addressing

This month I’m going to be a bit more technical and try and explain in layman’s term the way the Internet phone book works. Or simply said how a device on a network is identified and how it calls to another device somewhere else on the network or Internet.

Every computer, smartphone, tablet, or IoT (Internet of Things, better said Internet connected device!) that communicates over a network has an “IP address” assigned to it that uniquely identifies the device and distinguishes it from other computers on the network. For the curious “IP” stands for “Internet Protocol”. This “IP address” is like a telephone number for the device and they currently come in 2 versions, IPv4 and IPv6. Generically you will find though that most devices still work on IPv4 which is easier to understand and for this article I’ll stick to IPv4 only.

An IPv4 address looks like www.xxx.yyy.zzz, an example would be

You will find that on your local network all devices will have similar numbering in the first portion, i.e. 192.168.0 and the last number (.123) is the device.
To segregate networks for both management of devices, but also to protect a set of devices from another, you will find the second to last number changes, thus 192.168.0.x is one set of devices, and 192.168.1.y is another set of devices. (note the first example has a “0” in the third position and the second example has a “1” in the third position) On a local network we call this segregation “VLANs”.

This is how we separate the crew network from the guest network for instance.

This separation is controlled by a “router” or “router/firewall” (often a ‘Kerio’ on board the yachts). And therefore, this router controls (and thus also blocks) the flow of traffic between the networks (vlans) and also the internet.

Now here comes a crunch point… under the IPv4 addressing scheme there are only 4.3 billion addresses. Enough you say? Well on today’s count there are some 22 billion internet connected devices at the beginning of 2019, and it is said we are currently around 31 billion devices. The forecast put it at 75.44 billion devices worldwide by 2025. So simply put there aren’t enough addresses to go unique on every device!

So, 2 things are done. The IP address you have on your device is not necessarily the address the other device that you happen to talk to at any time sees, your router/firewall does address translation, and the IP address the “outside” world sees is another one that was appointed to your firewall.

Have a look on your personal device and in the settings,  you should find what your IP address it has, then go to the website https://whatsmyIPaddress.com and you will see a different address, basically this is the address the “outside” world sees. This “outside” IP address is the same from any device on your local network. One note to make here, if you have multiple connection to the internet, cellular, vsat, landline, etc.. each of these have a separate unique “outside” IP address. You may find that your crew networked device is routed through the cellular link, whilst your guest networked device is routed through the VSAT link, and therefore you get a different “outside” IP address on your https://whatsmyIPaddress.com check!

This is how your local network can be set up with your router/firewall doing all the hard work, traffic policing of what information goes where… i.e. is the traffic local, is it for the internet and so on. 

So how do we convert a domain name “http://teletechnics.com” to an IP address, or technically said, how do we match URL (Unique Resource Locator) to an IP address. Well there is an enormous phone book located on the internet! In IT speak we call it a DNS, a Domain Name System. So, when you want to go to teletechnics.com, you first have to go to your local DNS and it will tell you the IP address of that domain. And then with that information you can “dial” the IP address and connect to the device that holds the information you seek under that domain name. Luckily your computer does this in a flash and you hardly notice the action. Although sometimes you sit there waiting for a while… why isn’t that website showing, since google seemed really fast… a reason can be that this DNS lookup is just taking a little longer than it should!

This article was written by Tim Gorter, teletechnics.com. Teletechnics provides full shoreside support to Superyacht engineers and ETO’s, providing remote monitoring as well as specialising in troubleshooting and analytic maintenance. Join the workshops organised in Barcelona during the winter months, more on teletechnics.com