1.7 Calculating IPv4 Subnets and Hosts

VLSM

• Subnet masks with varying lengths

• Allows us to make our network as small and as large as we want it

• Ex. 10.0.1.0/24 or 10.0.8.0/26 would be variable… even though 10 is class A and would usually use 255.0.0.0, or /8, we’re making it whatever we want!

Example of VLSM

• IP address 10.0.0.0 usually has subnet mask 255.0.0.0

• But with VLSM, we can borrow however many bits we need to create smaller subnets, ex. 255.255.255.0; we’re taking the middle 2 octets to create a /24 subnet

2^subnet bits

Calculating total subnets

2^host bits - 2

Calculating hosts per subnet

• The 2 is subtracted because that’s our network address and our broadcast address

65,536, 254

IP address: 10.1.1.0/24

Total subnets: _______

Hosts per subnet: ______

4, 62

IP address: 192.168.11.0/26

Total subnets: ______

Hosts per subnet: ______

32, 2,046

IP address: 172.16.55.0/21

Total subnets: ______

Hosts per subnet: ______