Examkin

Question

Difficulty: MediumIPv4 Addressing and Subnetting

A network administrator is allocating IP addresses for a high-availability firewall cluster. The segment is assigned a subnet mask of 255.255.255.248255.255.255.248. How many usable host IP addresses are available for assignment in this subnetwork?

Answer: 6 addresses

Answer

There are 6 usable host IP addresses available in a subnetwork assigned a 255.255.255.248255.255.255.248 subnet mask.
A subnet mask of 255.255.255.248255.255.255.248 corresponds to a /29/29 CIDR prefix length. This leaves 3 host bits (32−29=332 - 29 = 3), providing 23=82^3 = 8 total IP addresses per subnet block. Subtracting 2 for the network ID (all host bits 0) and the directed broadcast address (all host bits 1) leaves exactly 6 usable host IP addresses.

Step-by-Step Solution

1
Calculate the total block size of IP addresses in the subnet
256−248=8256 - 248 = 8 total IP addresses
The subnet mask octet of 248 indicates a block size of 8 total addresses (23=82^3 = 8 host bits).
2
Subtract reserved network and broadcast addresses
8−2=68 - 2 = 6 usable host IP addresses
The network ID (first address) and broadcast address (last address) cannot be assigned to hosts.

Key Concept

Calculating Usable Host IP Addresses from Subnet Masks
Estimated Time:1m 0s
Rate this question

Topics

IPv4 Addressing and Subnetting

More questions from this topic