Ip address: quick revision, 14 bites

IP Address as a Unique Network Identifier

Every device needs a unique address.

An **IP address** (Internet Protocol address) is a numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication. It serves two main functions: **host or network interface identification** and **location addressing**. Think of it like a mailing address for you…

Takeaway. An IP address uniquely identifies a device on a network, enabling data to be routed to the correct destination.

IPv4 vs. IPv6

Two versions, vastly different sizes.

Takeaway. IPv4 is the older, more common standard, but IPv6 is necessary to accommodate the growing number of internet-connected devices.

The Two Parts of an IP Address

Network part and host part.

Every IP address is logically divided into two parts: the **network portion** and the **host portion**. The network portion identifies the specific network the device belongs to, while the host portion identifies the specific device on that network. The **subnet mask** determines where this division occurs.

Takeaway. An IP address's network part routes data to the right network; the host part delivers it to the right device.

Subnet Mask and Binary Representation

The mask reveals the network.

A **subnet mask** is a 32-bit number that masks the IP address to separate the network and host portions. In binary, the mask has a contiguous block of 1s for the network part and 0s for the host part.

Takeaway. The subnet mask, when ANDed with the IP address, reveals the network address.

IP Address Classes (Classful Networking)

Old-school way to split networks.

Takeaway. IP classes A, B, and C define fixed network/host boundaries, but modern networking uses classless CIDR for flexibility.

Confusing Public vs. Private IP Addresses

Not all IPs are internet-routable.

A common mistake is thinking every IP address is globally unique and routable on the internet. **Private IP addresses** (e.g., `10.0.0.0/8`, `172.16.0.0/12`, `192.168.0.0/16`) are reserved for internal networks and are not routed on the public internet. They require **NAT** (Network Address Translation) to communicate…

Takeaway. Private IPs are for internal use only; public IPs are globally unique and internet-routable.

How Your Home Router Uses IP Addresses

Your router is a NAT gateway.

Your home router gets one **public IP** from your ISP. All your devices (phone, laptop, smart TV) get **private IPs** like `192.168.1.x`. When you browse the web, the router uses **NAT** to translate your private IP to its public IP, keeping track of which device requested what. This is why multiple devices can share o…

Takeaway. NAT allows many private IPs to share a single public IP, conserving global address space.

Finding Your IP Address (Windows & Mac)

Quick steps to check your IP.

Takeaway. You can find your private IP via system commands and your public IP via online tools.

CIDR Notation – /24, /16, /8

Slashes simplify subnet masks.

**CIDR** (Classless Inter-Domain Routing) notation uses a slash followed by the number of bits in the network prefix. For example, `192.168.1.0/24` means the first 24 bits are the network part (same as `255.255.255.0`). A `/16` gives 65,534 hosts, a `/24` gives 254 hosts.

Takeaway. CIDR notation (e.g., /24) compactly represents the subnet mask and host capacity.

Subnetting a /24 Network

Splitting a network into smaller pieces.

Suppose you have `192.168.1.0/24` and need 4 subnets. Borrow 2 bits from the host portion: new mask = `/26` (255.255.255.192). Each subnet has $2^6 - 2 = 62$ usable hosts. The subnets are: `192.168.1.0/26`, `192.168.1.64/26`, `192.168.1.128/26`, `192.168.1.192/26`.

Takeaway. Borrowing host bits creates more subnets, each with fewer hosts.

Remembering Private IP Ranges

10, 172.16, and 192.168.

Use the mnemonic: **10** is the big one (Class A), **172.16** is the medium one (Class B), and **192.168** is the small one (Class C). Think: '10 big, 172 medium, 192 small'.

Takeaway. Private IP ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.

Network Address vs. Broadcast Address

First and last addresses are special.

In any subnet, the **first address** (all host bits 0) is the **network address** and cannot be assigned to a device. The **last address** (all host bits 1) is the **broadcast address**, used to send data to all devices on that subnet. Usable host addresses are everything in between.

Takeaway. Always subtract 2 from the total host count: one for network, one for broadcast.

IPv4 Address Exhaustion

We ran out of IPv4 addresses.

The last blocks of IPv4 addresses were allocated by IANA in 2011. This scarcity is the main reason IPv6 was developed and why NAT is so widely used. Without NAT and private IPs, the internet would have run out of addresses much sooner.

Takeaway. IPv4 exhaustion drove the adoption of IPv6 and NAT.

Using Static vs. Dynamic IPs

Static for servers, dynamic for clients.

**Static IPs** are manually assigned and never change — ideal for servers, printers, or network devices that need a fixed address. **Dynamic IPs** are assigned automatically by **DHCP** (Dynamic Host Configuration Protocol) and can change over time — best for client devices like laptops and phones.

Takeaway. Use static IPs for devices that must always be reachable; use DHCP for everything else.