Asus CX200 - Manual (Page 90)

ASUS CX200 Internet Camera
A subnet mask is a 32-bit value that distinguishes the network ID from
the host ID for different sub-networks on the same logical network. Like
IP addresses, subnet masks consist of four octets in dotted decimal
notation. You can use subnet masks to route and filter the transmission
of IP packets among your sub-networks. The value “255” is assigned to
octets that belong to the network ID, and the value “0” is assigned to
octets that belong to the host ID.
For the example above, if you want all the devices on the sub-networks
to receive each other’s IP packets, set the subnet mask to 255.255.0.0.
If you want the devices on a single sub-network only to receive IP
packets from other devices on its own sub-network, set the subnet mask
to 255.255.255.0 for the devices on the sub-network.
Subnet Mask Routing and Filtering
0.0.0.0 IP packets are transmitted to all devices.
255.0.0.0 IP packets are only transmitted to devices that
are IP that’s first octet matches the sender’s IP
address’s first octet.
255.255.0.0 IP packets are only transmitted to devices
that are IP that’s first two octets match the
sender’s IP address’s first two octets.
255.255.255.0 IP packets are only transmitted to devices
that are IP that’s first three octets match the
sender’s IP address’s first three octets.