What a /27 subnet is: an eighth of a /24
A /27 holds 32 addresses, 30 usable, and divides a /24 into eight subnets with a block size of 32 in the last octet.
At a glance
- Subnet mask
- 255.255.255.224
- Wildcard mask
- 0.0.0.31
- Total addresses
- 32
- Usable hosts
- 30
- Block size in the last octet
- 32
- Host bits
- 5 of 32
In detail
The mask is 255.255.255.224. Thirty usable addresses is the smallest subnet that still feels like a normal network rather than a point-to-point link.
Right for a small DMZ, a management network, a load balancer tier, or a handful of appliances that each need an address and a little room to grow.
Count the addresses you actually need including the gateway, the virtual addresses for any load balancer, and anything the platform reserves. Thirty goes faster than it looks.
Examples
10.0.3.0/27 .0 to .31 usable .1 to .30
10.0.3.32/27 .32 to .63 usable .33 to .62
10.0.3.64/27 .64 to .95 usable .65 to .94
...
10.0.3.224/27 .224 to .255 usable .225 to .254Things that catch people out
- Valid last octets for a /27 network address are multiples of 32: 0, 32, 64, 96, 128, 160, 192, 224.
- Some cloud providers set a minimum subnet size larger than a /27, so a design built on /27s will not deploy there.
Try it: IP Subnet Calculator
Enter any IPv4 address with a prefix or a dotted mask and get the network address, broadcast address, wildcard mask, usable host range, address class, and the hex and binary forms.
IP Subnet Calculator
LOCAL · Browser-OnlyCalculate IP subnet details, network ranges, and CIDR notation
192.168.1.0192.168.1.255255.255.255.00.0.0.255192.168.1.0/24192.168.1.1 - 192.168.1.254192.168.1.1192.168.1.254256254C0xC0A8016411000000.10101000.00000001.01100100Split into two /25 subnets
Dividing 192.168.1.0/24 one prefix deeper.
Common Subnet Masks
Related IPv4 subnets
All ipv4 subnets →What a /26 subnet is: a quarter of a /24
A /26 uses the mask 255.255.255.192 and gives 62 usable addresses. What it is for and where it goes wrong.
What a /28 subnet is: sixteen addresses
A /28 uses the mask 255.255.255.240 and gives 14 usable addresses. What it is for and where it goes wrong.
What a /24 subnet is: the classic LAN subnet
A /24 uses the mask 255.255.255.0 and gives 254 usable addresses. What it is for and where it goes wrong.
What a /29 subnet is: eight addresses
A /29 uses the mask 255.255.255.248 and gives 6 usable addresses. What it is for and where it goes wrong.
What a /30 subnet is: a point-to-point link
A /30 uses the mask 255.255.255.252 and gives 2 usable addresses. What it is for and where it goes wrong.
What a /31 subnet is: a point-to-point link with no waste
A /31 uses the mask 255.255.255.254 and gives 2 usable addresses. What it is for and where it goes wrong.
Tools for this
- IP Subnet Calculator Free online IP subnet calculator - calculate IP subnet details, CIDR notation, and network address ranges
- IP Address Lookup Free online IP address lookup - find your public IP address and basic network information
- Number Base Converter Free online number base converter - convert numbers between decimal, binary, octal, and hexadecimal