IP Addressing

If a router, or a PC has multiple interfaces, each interface will have its own IP address.

Various methods are used to divide IP networks into subnets.

Fixed Length Subnet Mask (FLSM)

A method of dividing an IP network into subnets where each subnet is of equal size and uses the same subnet mask. All subnets have the same host capacity.

Easier for network planning. But sometimes less efficient.

Variable Length Subnet Mask (VLSM)

Allows a network to be divided into subnets of different sizes, each with its own subnet mask. Enables more efficient use of IP address space.

Managed by carefully planning the network, starting with the largest required subnets and working down to the smallest, ensuring that address ranges do not overlap.

Classfull Addressing

An obsolete method. Network and host part of the IP address are divided based on fixed classes.

Class	Starting Bits	Address Range	Network Bits	Host Bits	No. of Networks	Hosts per Network
A	0	1.0.0.0 – 126.255.255.255	8	24	128	16,777,214
B	10	128.0.0.0 – 191.255.255.255	16	16	16,384	65,534
C	110	192.0.0.0 – 223.255.255.255	24	8	2,097,152	254
D	1110	224.0.0.0 – 239.255.255.255	—	—	—	Multicasting
E	1111	240.0.0.0 – 255.255.255.255	—	—	—	Experimental

CIDR

Short for Classless Inter-Domain Routing. A method of allocating IP addresses that allows for more efficient use of IP addresses.

IP address is divided into 2 parts:

• subnet part: same for all devices in the subnet
• host part: different for each host

Address format

192.168.12.0/24

Here the ending 24 defines the length of subnet part.