Introduction
Every device that talks over the Internet or a TCP/IP network needs a unique numeric label so that data can be delivered to exactly the right place. That label is the IP address. IP addressing is the scheme that assigns these labels; subnetting is the technique of slicing one large address block into several smaller, well-organised networks.
For BCS, Bank IT, and IT-officer exams this topic is a guaranteed scorer. Questions almost always involve counting — how many hosts, how many subnets, what is the network address, what is the broadcast address, which mask to use. If you master the binary logic and a handful of formulas, these become fast, certain marks. This lesson builds everything from first principles so nothing is memorised blindly.
Learning objectives
By the end of this lesson you should be able to:
- Explain what an IPv4 address is and convert freely between binary and dotted-decimal form.
- Identify the class (A, B, C, D, E) of any address and state its default mask.
- Distinguish the network portion from the host portion using a subnet mask.
- Use CIDR (slash) notation and translate it to and from a dotted-decimal mask.
- Subnet a network: compute the number of subnets, hosts per subnet, network address, broadcast address, and the usable host range.
- Apply VLSM to allocate address space efficiently.
- Recognise private, reserved, loopback and special addresses, and know the basics of IPv6.