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TechKnowSurge Catalog Interactives Class B and A Subnet Range Calculator
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Class B and A Subnet Range Calculator

Subnet a Class B or Class A network to a stated need, then type the network, broadcast and usable range of a numbered subnet.

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

About this interactive

Subnetting a Class B or a Class A network uses the same steps as a Class C. Only the size of the numbers changes. Class B has 16 host bits to borrow from and Class A 24, so the subnet boundary usually lands in the third or the second octet, and each subnet spans whole octets. 172.40.0.0 split into /21 subnets steps by 8 in the third octet: 172.40.0.0, 172.40.8.0, 172.40.16.0. The third subnet runs from 172.40.16.0 to 172.40.23.255. The octets after the boundary are all host bits. In the network address they are all 0, and in the broadcast address they are all 255, which is why a broadcast like 172.40.23.255 ends in .255 and the next network starts at 172.40.24.0. Taking one away from a network address borrows from the octet before it: one below 172.40.24.0 is 172.40.23.255. On a Class A, once the third octet runs out the network addresses carry over into the second: the fifth /17 subnet of 10.0.0.0 is 10.2.0.0. Type addresses in dotted decimal. Anything you miss shows the answer and how to work it out. Seven of the twenty-two 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

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.
Custom Subnet Mask
A subnet mask that draws the network/host boundary at a point other than the classful boundary, allowing flexible division of network and host bits.
Borrowed Bits
Host bits reallocated to the network portion of a subnet mask to create additional subnets, reducing the number of available hosts per subnet.
Class A Network
An IPv4 address class using the range 1–126 in the first octet, with a default subnet mask of 255.0.0.0, providing a large number of host addresses.

Topics

Subnetting Network Address Broadcast Address Usable Host Range Interactive Calculation

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