/27 Subnet Mask 255.255.255.224, 30 Usable Hosts, CIDR Explained

User question

what is a /27 subnet mask

Artificial Intelligence Response

Direct answer to the question

A /27 subnet mask in IPv4 means:

• 27 bits are used for the network portion
• 5 bits are left for host addresses
• Its dotted-decimal form is 255.255.255.224

Key points:

• Binary mask: 11111111.11111111.11111111.11100000
• Total addresses per subnet: \(2^5 = 32\)
• Usable host addresses: 30
  (2 are normally reserved: network address and broadcast address)
• Subnet increment/block size: 32

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Detailed problem analysis

IPv4 addresses are 32 bits long. A subnet mask tells you which bits identify the network and which bits identify the host.

For /27:

• The first 27 bits are 1 in the mask
• The remaining 5 bits are 0
• That gives:

\[ 32 - 27 = 5 \text{ host bits} \]

So the number of addresses in each /27 subnet is:

\[ 2^5 = 32 \]

In traditional IPv4 subnetting:

• 1 address is the network address
• 1 address is the broadcast address
• So usable hosts are:

\[ 32 - 2 = 30 \]

The mask in binary is:

11111111.11111111.11111111.11100000

The last octet 11100000 equals:

\[ 128 + 64 + 32 = 224 \]

So the subnet mask is:

255.255.255.224

Example

For the subnet 192.168.1.0/27:

• Network address: 192.168.1.0
• Usable hosts: 192.168.1.1 to 192.168.1.30
• Broadcast address: 192.168.1.31

The next /27 subnet starts at 192.168.1.32, then 192.168.1.64, and so on.
That is because the block size is:

\[ 256 - 224 = 32 \]

So /27 subnets increment by 32 in the last octet:

• .0
• .32
• .64
• .96
• .128
• .160
• .192
• .224

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Current information and trends

The concept of a /27 remains standard in IPv4 networking and is still commonly used for:

• small VLANs
• office segments
• DMZ segments
• management networks
• small server or device groups

Although IPv6 adoption continues, IPv4 subnetting with CIDR notation like /27 is still widely used in enterprise, industrial, and embedded networking.

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Supporting explanations and details

A useful way to think about /27 is:

• A /24 gives 256 total addresses
• Splitting a /24 into /27 networks creates:

\[ 2^{27-24} = 2^3 = 8 \text{ subnets} \]

Each subnet has:

• 32 total addresses
• 30 usable hosts

Example inside a /24

If you split 192.168.1.0/24 into /27s, the first few are:

Subnet	Usable range	Broadcast
192.168.1.0/27	192.168.1.1–192.168.1.30	192.168.1.31
192.168.1.32/27	192.168.1.33–192.168.1.62	192.168.1.63
192.168.1.64/27	192.168.1.65–192.168.1.94	192.168.1.95

This is useful when you want smaller broadcast domains and better address efficiency than a full /24.

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Ethical and legal aspects

For subnetting itself, there are no major ethical issues, but in practice:

• poor subnet design can expose devices unintentionally
• incorrect segmentation can weaken security
• proper subnet planning supports safer network isolation and access control

In regulated environments, correct segmentation may also help with compliance requirements for:

• internal security zones
• device separation
• logging and access management

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Practical guidelines

When working with a /27 subnet, remember:

• Mask: 255.255.255.224
• Addresses per subnet: 32
• Usable hosts: 30
• Step size: 32

Best practices:

• verify that the default gateway is inside the correct /27 range
• do not assign the first address as a host if it is the network address
• do not assign the last address if it is the broadcast address
• check for subnet mask mismatches during troubleshooting

A quick test:

• If an IP is 192.168.1.45/27, it belongs to the subnet 192.168.1.32/27
• Usable range: 192.168.1.33 to 192.168.1.62
• Broadcast: 192.168.1.63

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Possible disclaimers or additional notes

• The “30 usable hosts” rule assumes traditional IPv4 subnet behavior with reserved network and broadcast addresses.
• This answer applies to IPv4. In IPv6, “/27” means something entirely different because IPv6 uses 128-bit addresses.

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Suggestions for further research

If you are learning subnetting, the next useful topics are:

• how to find the network and broadcast address from any IP/CIDR
• differences between /24, /26, /27, /28
• VLSM (Variable Length Subnet Masking)
• VLAN and subnet design in real networks

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Brief summary

A /27 subnet mask means:

• CIDR: /27
• Subnet mask: 255.255.255.224
• Host bits: 5
• Total addresses: 32
• Usable hosts: 30
• Increment: 32

If you want, I can also show you a quick trick to calculate any /27 subnet range in seconds.

Disclaimer: The responses provided by artificial intelligence (language model) may be inaccurate and misleading. Elektroda is not responsible for the accuracy, reliability, or completeness of the presented information. All responses should be verified by the user.