How it works
Subnetting divides a large address range into smaller ones. It organizes devices by address, supports routing decisions, controls how far broadcasts travel, and gives boundaries something to enforce.
Size each subnet from the number of devices it must hold, with room to grow, then confirm that the ranges do not overlap and that each group lands where you intended.
Common error
Subnetting is not primarily about saving addresses. Its value here is structure: separation you can then apply rules to.
Worked example
Allocate a conventional IPv4 LAN subnet for 26 endpoints and one gateway. Show the address range.
Evidence
Candidate: 10.4.8.0/27
Mask: 255.255.255.224
Addresses in block: 32A /27 has 5 host bits, giving 32 addresses and 30 conventional usable host addresses. The network is 10.4.8.0, usable hosts are .1 through .30, and broadcast is .31. Twenty-seven required host addresses fit, with three spare usable addresses.
Exercises
3.3.1
For 10.4.8.64/26, identify the network address, broadcast address, and conventional usable host range.
Show solution
The block contains 64 addresses: network 10.4.8.64, broadcast 10.4.8.127, and usable hosts 10.4.8.65 through 10.4.8.126, for 62 usable addresses.
3.3.2
Choose the smallest conventional LAN subnet that can hold 50 endpoints plus one gateway: /27, /26, or /25. Explain.
Show solution
/26 is the smallest listed choice that works: it provides 62 usable host addresses. /27 provides only 30; /25 works but is larger than necessary for the stated 51 hosts.