IP Addressing is the method of assigning unique identifiers to devices on a network. Subnetting is the process of dividing a larger network into smaller, more efficient subnetworks. Together, they define how data is routed and how devices communicate in a networked environment.
An IP address is a numerical label assigned to each device on a network.
| Class | Range | Default Subnet Mask | Usage |
|---|---|---|---|
| A | 1.0.0.0 – 126.255.255.255 | 255.0.0.0 | Large networks |
| B | 128.0.0.0 – 191.255.255.255 | 255.255.0.0 | Medium-sized networks |
| C | 192.0.0.0 – 223.255.255.255 | 255.255.255.0 | Small networks |
| D | 224.0.0.0 – 239.255.255.255 | N/A | Multicasting |
| E | 240.0.0.0 – 255.255.255.255 | N/A | Reserved |
Used for internal networks (not routable on the internet):
Subnetting is dividing a network into smaller logical units (subnets) to improve performance, security, and address management.
A Subnet Mask determines which part of an IP address is the network and which is the host.
| CIDR Notation | Subnet Mask | # of Hosts |
|---|---|---|
| /24 | 255.255.255.0 | 254 |
| /25 | 255.255.255.128 | 126 |
| /26 | 255.255.255.192 | 62 |
| /30 | 255.255.255.252 | 2 |
Host bits are the number of bits left for the host portion in an IP address after subnetting.
You subtract 2 because:
If you have a /24 subnet:
Let me know if you want help calculating host counts for specific CIDR blocks!
| Type | Description |
|---|---|
| Network Address | First IP in a subnet (identifies the subnet) |
| Broadcast Address | Last IP in a subnet (used to broadcast to all hosts) |
| Host Address | All usable IPs between network and broadcast addresses |
| Loopback | 127.0.0.1 — used to test local networking |
| APIPA | 169.254.x.x — self-assigned when DHCP fails |
| Method | Description |
|---|---|
| Static IP | Manually configured; used for servers, printers, critical devices |
| Dynamic IP | Automatically assigned by DHCP server; used for regular clients |
ipconfig / ifconfig: View current IP configurationping: Test network connectivitysubnet calculators: Plan subnet sizestracert / traceroute: Trace packet pathipcalc, cidr.xyz: Online subnetting tools🧭 Understanding IP addressing and subnetting is foundational for designing secure, efficient, and scalable networks.