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TechKnowSurge Catalog Interactives Classful Network Range Calculator
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Classful Network Range Calculator

Read an IPv4 address's class from its first octet, then type its classful network address, broadcast address and usable range, or a class's network and host counts.

⚑ Complete this interactive to capture a CTF flag worth 5 points.

About this interactive

Classful addressing splits an IPv4 address into a network part and a host part at an octet boundary, and the first octet says where. Class A starts with the bit 0, so its first octet runs from 0 to 127 (0 and 127 are reserved, leaving 1 to 126); its first octet is network and the last three are host. Class B starts with 10, first octet 128 to 191, two octets of network and two of host. Class C starts with 110, first octet 192 to 223, three octets of network and one of host. Class D (1110, 224 to 239) is multicast and Class E (1111, 240 to 255) is experimental; neither has a network and host split. Once you know the class, the rest is the same three moves. Set every host octet to 0: that is the network address, the first address of the range. Set every host octet to 255: that is the broadcast address, the last address. The usable hosts are everything between, from the network address plus one to the broadcast address minus one. 172.18.254.37 is Class B, so its network is 172.18.0.0, its broadcast 172.18.255.255, and its usable range 172.18.0.1 to 172.18.255.254. Counting works on bits. Host bits give the addresses in a network, 2 to the power of the host bits, minus 2 for the network and broadcast addresses: 254 for Class C, 65,534 for Class B, 16,777,214 for Class A. The network bits left after the leading bits give the number of networks: 2^7 = 128 for Class A, 2^14 = 16,384 for Class B, 2^21 = 2,097,152 for Class C. Assume classful boundaries throughout: no subnetting yet. Type addresses in dotted decimal and counts in digits (commas are fine). Anything you miss shows the answer and how to work it out. Seven of the twenty-five questions are drawn each run.

What you'll learn

Aligned to

CompTIA Network+
1.7 Given a scenario, use appropriate IPv4 network addressing.
Cisco CCNA
1.6 Configure and verify IPv4 addressing and subnetting
Cisco CCST Networking
2.2 Identify IPv4 addresses and subnet formats

Key terms

IPv4 Address Class
One of five categories (A–E) into which IPv4 addresses are grouped based on leading bit patterns, each defining a specific range of addresses and a fixed network-to-host bit boundary.
Classful Addressing
An early IPv4 addressing scheme that divided the address space into fixed classes (A, B, and C for hosts; D for multicast; E reserved) based on the leading bits of the address, with each class defining a fixed boundary between the network and host portions. Classful addressing was replaced by CIDR because it wasted large blocks of address space.
Network Portion
The bits of an IPv4 address that identify the specific network, determined by the address class in classful addressing.
Host Bits
The portion of an IPv4 address that identifies individual devices within a network segment, as determined by the subnet mask.
Network Address
The first address in an IP network range that identifies the network itself and cannot be assigned to a host. It is formed when all host bits are set to zero.
Broadcast Address
The last address in an IP subnet range, formed when all host bits are set to one, used to send a single packet to every device on that network simultaneously.
Usable Host Range
The set of IP addresses within a subnet that can actually be assigned to network devices, spanning from one address above the network address to one address below the broadcast address. For example, in the 192.168.1.0/24 network, the usable host range is 192.168.1.1 through 192.168.1.254.
Usable Hosts
The number of valid host addresses within a subnet, calculated by subtracting two from the total host count to exclude the network and broadcast addresses.

Topics

Classful Addressing Network Address Broadcast Address Usable Host Range Interactive Calculation

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