11.3.1 Device Addressing

Learn the numbering systems and standards used to identify network devices.

IP addresses are based in the three numbering system used by computers:

• decimal (base 10)
• binary (base 2)
• hexadecimal (base 16)

Hexadecimal is a special number system. Since the Latin-based languages only have 10 digits (0-9), but hexadecimal digits represent (0-15), we borrow the letters (A-F) to represent the missing digits (10-15). This shortening is why hexadecimal is used to shorten incredibly long binary numbers, which are still too long in decimal for computer technicians to bother with.

Physical Addresses

The IEEE requires all NICs to have a Media Access Control (MAC) address. It's a 48-bit hexadecimal number that's hardcoded into the NICs ROM at manufacturing time. All MAC addresses are unique. The first half of the 48-bit identifier is used to pinpoint the manufacturer. Every NIC manufacturer in the world is assigned a unique six-digit sequence by the IEEE. The rest of the number is randomized, unique to that device.

Any data packet that's being sent using a NIC has the NICs MAC address embedded in the packet's header.

Logical Addresses

Logical addresses are assigned using software, which means that they can be assigned and removed as needed. Different Internet protocols have different logical addresses, but the most common ironically we're apparently running out of these is IPv4 addresses.

An IPv4 address consists of four decimal numbers ranging from (0-255) 4 u8 / ushorts. On a network, each node has to have both a unique IP address and their native MAC address. When data needs to be sent between two nodes, a first packet is sent from the node to the network containing the sender's MAC address and the recipient's IP address in the header. It's then up to the network router or switch to find the device it needs to communicate with to handle the outgoing packet.

When a network node wants to send data, it uses something called the Address Resolution Protocol (ARP) to ask the others nodes on the network with a specific IP address to reply to the broadcast with it's MAC address.

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