Subnetting

Question 1

CIDR

Answer 1

Classless Inter-Domain Routing:

Removed the fixed /8, /16, and /24 requirements for address classes
Allowed them to be split/subnetted to smaller networks

Ex: 175.10.10.0/20

Question 2

Calculating Number of Subnets

Answer 2

2 ^ Subnet bits

Question 3

Calculating Number of Hosts

Answer 3

(2 ^ Host Bits) - 2

Question 4

IP subnet-zero

Answer 4

We used to have to subtract 2 to get the number of available networks as well (wasted address space with no use case)

This command overrides this limitation and is enabled by default

Question 5

VLSM

Answer 5

Variable Length Subnet Masking:

Early routing protocols only supported fixed length subnet masking (FLSM)
Where all subnets had to be the same size

All modern routing protocols support VLSM (Variable Length Subnet Masking)
Allows us to size subnets differently according to how many hosts they have

Question 6

/31 vs. /30

Answer 6

Both of these subnets accommodate 2 hosts per subnet
/31 supports 128 subnets, /30 only 64
/31 is useful if you need to maximize address space
/30 is more standard & commonly used

For CCNA: Use a /30 when a subnet to support 2 hosts is required, unless told to use /31