Why does a /27 give 30 usable addresses and not 32?

A /27 is 32 addresses. The first is the network address. The last is the broadcast address. Neither is a host address on a normal subnet, so 30 remain.

What changes on a /31?

RFC 3021 uses both addresses on a point-to-point link. There is no unused network or broadcast address, so a /31 reports two usable addresses, not zero. A /32 is the single host.

How do static addresses and DHCP reservations differ for cameras?

A static address is set on the device. A DHCP reservation is assigned by the server when the device asks. Both can hold the same number. A static camera inside the DHCP pool and a lease for that number are two claims on one address.

What to send back when IT asks for a device list?

The assignment table has address, label, and group. Copy CSV for a spreadsheet or VMS import. Copy the plain list for email. The remaining free count and any reserved ranges stay on the same picture.

Subnet and CIDR

Usable range, mask, and a device assignment list from the IPv4 block IT supplied. IPv6 is not covered.

The mask marks which bits belong to the network. On a normal subnet the first address is the network and the last is the broadcast; those two are not cameras or controllers. A broadcast storm on a camera VLAN is every camera answering a flood of broadcast frames on the same segment. A static camera sitting inside the DHCP pool eventually shares a number with a lease.

Subnet calculator

Paste the block IT handed you. Usable range, mask, and an assignment list stay in the URL. IPv4 only.

Starting points

Inputs

Block

Address or CIDR

192.168.1.0/27, 192.168.1.130/26, or 10.5.7.130 255.255.255.192.

Address

Used when the address and the prefix are picked separately.

Prefix

Common prefixes

Results

Usable range

192.168.1.1 – 192.168.1.30

Pass

Usable 192.168.1.1 – 192.168.1.30.

Block

Network

192.168.1.0

Broadcast

192.168.1.31

Mask

255.255.255.224

Prefix

/27

Wildcard

0.0.0.31

Total addresses

Usable addresses

Class

Class C

Scope

RFC 1918 private (192.168.0.0/16)

Binary

Mask 11111111.11111111.11111111.11100000

Network 11000000.10101000.00000001.000xxxxx

x marks host bits.

Assignment

Remaining free

Address	Label	Group
192.168.1.0	Network
192.168.1.1	Gateway
192.168.1.31	Broadcast

Worked example

192.168.1.0/27 has mask 255.255.255.224. The network is 192.168.1.0. The broadcast is 192.168.1.31. Usable addresses are 192.168.1.1 through 192.168.1.30, 30 hosts.

How to use

Paste the block as CIDR (192.168.1.0/27), a host inside a block (192.168.1.130/26), or an address and a dotted mask.
The usable range is the first host through the last host. On a normal subnet the network and broadcast addresses are not host addresses.
Use the planner to park a gateway and reserved ranges, then assign device groups from the lowest free address. Copy the list as CSV or plain text.

Assumptions

IPv4 only. IPv6 is not covered.
The block and any reserved ranges are whatever IT provided.
The VLAN, the gateway, and the DHCP scope belong to the network owner.
An address plan is worth confirming with IT before it goes on cameras or controllers.
A /31 uses both addresses on a point-to-point link (RFC 3021). A /32 is a single host.

FAQ

Why does a /27 give 30 usable addresses and not 32?: A /27 is 32 addresses. The first is the network address. The last is the broadcast address. Neither is a host address on a normal subnet, so 30 remain.
What changes on a /31?: RFC 3021 uses both addresses on a point-to-point link. There is no unused network or broadcast address, so a /31 reports two usable addresses, not zero. A /32 is the single host.
How do static addresses and DHCP reservations differ for cameras?: A static address is set on the device. A DHCP reservation is assigned by the server when the device asks. Both can hold the same number. A static camera inside the DHCP pool and a lease for that number are two claims on one address.
What to send back when IT asks for a device list?: The assignment table has address, label, and group. Copy CSV for a spreadsheet or VMS import. Copy the plain list for email. The remaining free count and any reserved ranges stay on the same picture.

Disclaimer

Field estimate only. Manufacturer data, the authority having jurisdiction (AHJ), and current applicable code govern material and whether a circuit is energized. See the disclaimer.