Network Fundamentals Part 1
The Physical Layers
Computer Communication: A layered Model
The Computer network architecture is built on several hierarchical layers. Hierarchical means that the underlying layer has to be on order for the next layer to process. If there is an error on one of the layers, end-to-end communication will fail.
There are 2 defined concept models; The TCP/IP Model and the OSI Model. However, the TCP/IP model is more simple to understand.
I will explain all the layers in the TCP/IP Model. In Part 1, I will be covering the Datalink and the Physical Layer.
Layer 1: The Physical Layer
The physical layer represents the cables that are interconnecting computers and network devices. It could also be the 2.4GHz or 5GHz wavelengths (or even 6GHz if you have the latest technology) that carries the information wirelessly. It’s transport of on and off signals, i.e ones and zeroes [1’s and 0’s] or bits.
Think of this layer as the roads which the mailman is driving on. (or the air that takes the plane up in the sky if it is wireless or LTE, or a high-speed magnetic rail, if it is a fiber connection, etc…).
Troubleshooting Advice
This layer I think most people understand and can troubleshoot on their own.
Make sure the cable is connected properly;
Sometimes there might be a faulty cable;
or you are either too far away from the access point [aka. WiFi router];
or something in between is blocking its signals, like a concrete wall or metal plate. Wireless troubleshooting is really a skill of it’s own.
Privacy Concerns Regarding the Physical Layer (especially LTE, i.e. 3G, 4G, and 5G)
If you want a fiber connection, your address will be registered to a connection number. If you want a mobile connection, a phone number will be registered in your name, and triangulation technology and Trilateration Technology will know where your LTE device is located. You simply can’t just anonymously connect to the Internet; unless you connect through your neighbors WiFi or something.
This data however should only be available to the ISP, which may give out your personal information for forensic purposes; if you are investigated for a criminal offense. With a cabled connection, they can’t prove any illegal activity beyond a reasonable doubt simply by capturing traffic from an address; because there might be multiple people living on the same address, behind the same connection. I will elaborate more on that further up in the TCP/IP stack.
Layer 2: The Datalink Layer
These are the hardware addresses of computers, phones, tablets, fridges, coffee makers, washing machines bla, bla, bla… and network devices. The most common type of hardware addresses are MAC=Media Access Control addresses, which operates on the ethernet standard. They are (or should be) unique identifiers of the machine, or the network card of the machine, more specifically.
If the cables are the roads, the MAC addresses are the persons that sends and receive packets along the roads.
A MAC address are 48bit in lenghts. It is represented by a 12 digit hexadecimal version of the binary bits and looks similar to this:
00:0C:12:34:AB:CD
You can probably spot one of them on a sticker underneath your WiFi router at home; or on the package of a newly bought phone.
For a visual representation of what Layer 2 connectivity looks like:
Summary:
There are 2 computers, with different MAC addresses. The network device in the middle keeps track of the computers MAC addresses and makes a interface to MAC binding. An interface in this case is a physical switchport.
The network device at this level, only performs switching. It does not require any additional information to send traffic between those 2 laptops. The hosts however, still needs to go through the upper layers.
The switch can use the same global MAC for all it’s ports, or use different MAC per port. It depends on the vendor of the device.
If we assume that this network device also performs routing, then it would be logical that the uplink WAN port is connected to the ISP. That will create a Layer 2 boundary between the ISP and the hosts inside the network. More on routing in the next layer.
How you calculate binary to hex or decimal, is beyond the scope of Network fundamentals. For most people, it is good enough to know how a MAC address looks like.
Unless you are in the IT business, it is very unlikely that you will see any other types of hardware addresses in a standard network today.
Troubleshooting Advice
There are seldom any issues in this layers. Usually it’s hardware related:
The cable is connected but the network adapter has been inactivated in the Operating System.
The network card in the computer is faulty.
The connected network device is faulty.
A theoretical issue could be that 2 machines have the same address, but that should never be the case.
Privacy Concerns Regarding MAC Addresses
These addresses never leaves the local network. That means these addresses ideally would only be known to you, the router and other locally connected devices in your home or workplace. However, certain application can ask for them for “security purposes”.
Since this address (in theory) should be unique in the whole world, it counts a personal information, but only if it’s tied to some other identifier. For example:
Let’s say you have a Telegram Account on your phone. Your phone has a phone number and a MAC address.
You give the phone number, which in most of the cases are registered in your name, and the MAC address to Telegram. That means that Telegram now knows that you own this specific phone.
You then download and install the Telegram application to your notebook, which has another unique MAC address. The Telegram app will then ask you to confirm that this new login from this device was really you, and you allow it from your phone. With almost 100% certainty, Telegram now knows that you own this specific notebook as well. This technique is called Device Chaining.
While this on the surface looks like a good practice to make sure no illegitimate person logs in on your Telegram account, It gives away a lot of private information that could be useful for a third party.
Almost all messaging platforms do this. It doesn’t necessarily mean that they are sharing information about our devices, but they could, if pressured by some government. The only messaging app I know of that doesn’t perform Device Chaining is Status.
Note: There are other privacy concerns regarding Internet Protocol version 6 that relates to MAC addresses, which is covered in the next layer.