What is a /27 subnet? 32 IPs for office VLANs and small server rooms

With 5 bits left for hosts, a /27 gives 2^5 = 32 addresses. Blocks step forward 32 addresses at a time. A /24 holds 8 of these blocks, and the first four in the last octet are .0-.31, .32-.63, .64-.95, .96-.127. The wildcard mask is 0.0.0.31, which is the subnet mask with every bit flipped. Access lists use that form to match a block.

Take the block at 192.168.1.32 as an example. Its usable addresses run 192.168.1.33 to 192.168.1.62, and its broadcast address is 192.168.1.63. Neither end of the block goes to a host, and that's the gap between the total and the usable count.

Pick a /27 for a segment that needs up to 30 devices on a conventional subnet. A /28 has 16 addresses and 14 usable, which can run short once a segment adds a few services. A /26 has 64 addresses and 62 usable, and it holds 2 /27 blocks.

Cloud limits apply too. AWS accepts subnets from /16 to /28, and Azure accepts /2 to /29, so a /27 is in range for both. Each one reserves five addresses in every subnet, which leaves 27 for resources. Size a cloud segment on that figure, not on the conventional count.