Question 1

What is CIDR notation?

Accepted Answer

CIDR (Classless Inter-Domain Routing) notation represents an IP address and its subnet mask in the format IP/prefix. For example, 192.168.1.0/24 means the first 24 bits are the network portion, giving a subnet mask of 255.255.255.0 with 254 usable hosts.

Question 2

How do I calculate usable hosts in a subnet?

Accepted Answer

Usable hosts = 2^(32 - CIDR prefix) - 2. You subtract 2 because one address is reserved for the network address and one for the broadcast address. For example, a /24 subnet has 2^8 - 2 = 254 usable hosts.

Question 3

What is a wildcard mask?

Accepted Answer

A wildcard mask is the inverse of a subnet mask. Where the subnet mask has 1s, the wildcard has 0s, and vice versa. Wildcard masks are commonly used in access control lists (ACLs) and OSPF configurations. For a /24 network, the wildcard mask is 0.0.0.255.

Question 4

What subnetting topics are on the Network+ exam?

Accepted Answer

CompTIA Network+ (N10-009) tests subnetting in objective 1.4. You should know how to: determine subnet masks from CIDR notation, calculate usable hosts, identify network and broadcast addresses, and understand classful vs classless addressing.

Question 5

What is the difference between /24 and /25?

Accepted Answer

A /24 subnet has 256 total addresses (254 usable) with mask 255.255.255.0. A /25 splits that in half: 128 total addresses (126 usable) with mask 255.255.255.128. Each additional bit in the prefix halves the number of available hosts.

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