How many /26 networks fit
| Parent block | Relationship |
|---|---|
| /8 | 262,144 × /26 fit inside one /8 |
| /16 | 1,024 × /26 fit inside one /16 |
| /24 | 4 × /26 fit inside one /24 |
4 × /26 = one /24. A /26 holds 2 × /27 or 4 × /28.
Worked example: 192.168.10.77/26
Exam-style question: what is the network, broadcast and usable range for 192.168.10.77/26?
- The mask is 255.255.255.192. The fourth octet (192) is the "interesting" one — the first that is not 255.
- Block size = 256 − 192 = 64. Networks start at multiples of 64 in the fourth octet: 0, 64, 128, …
- The fourth octet of 192.168.10.77 is 77. 77 ÷ 64 = 1 remainder 13, so the block starts at 1 × 64 = 64.
- Network = 192.168.10.64. Broadcast = 64 + 64 − 1 = 127, giving 192.168.10.127.
- Usable hosts: 192.168.10.65 to 192.168.10.126, which is 26 − 2 = 62 addresses.
Same thing in binary (network bits | host bits):
Address 11000000.10101000.00001010.01|001101 Mask 11111111.11111111.11111111.11|000000 Network 11000000.10101000.00001010.01|000000
Where /26 is used in real networks
-
Azure Bastion and Azure Firewall
Azure requires
AzureBastionSubnetandAzureFirewallSubnetto be at least a /26. Azure reserves 5 addresses in every subnet, so a /26 gives 59 usable. Check with the Azure subnet calculator. -
Small VLANs
Printers, IP phones on one floor, a lab rack, or building management systems: 62 hosts is enough for many single-purpose VLANs, and four of them fit in one /24.
Common /26 mistakes
- Getting the block wrong for addresses like .77. The blocks are 0, 64, 128, 192, so .77 is in the .64 block (hosts .65 to .126), not the .0 block.
- Creating an Azure Bastion subnet as a /27. Deployment fails; Azure needs /26 or larger for Bastion.
- Giving a VLAN a /26 when it will grow. Re-numbering later costs far more than starting with a /25 or /24.
/26 FAQ
How many hosts are in a /26?
62: 2^6 = 64 addresses minus network and broadcast.
What are the four /26 networks in a /24?
x.x.x.0/26, x.x.x.64/26, x.x.x.128/26 and x.x.x.192/26. Each covers 64 addresses.
What is the wildcard mask for /26?
0.0.0.63, which is one less than the block size of 64. In an ACL, 10.1.1.64 0.0.0.63 matches 10.1.1.64 to 10.1.1.127.
What subnet mask gives 62 hosts?
255.255.255.192 (/26). Six host bits give 64 addresses; minus network and broadcast leaves 62. Five host bits (a /27) would give only 30.