32
32
segments the network address into 100 subnetwork addresses.
(If the Class B network address is 150.1.x.x, the address can
be segmented further from 150.1.1.x through 150.1.100.x.)
A subnet mask is a 32-bit value that distinguishes the network
ID from the host ID for different subnetworks 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 subnetworks. 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
subnetworks to receive each other’s IP packets, set the subnet
mask to 255.255.0.0. If you want the devices on a single
subnetwork only to receive IP packets from other devices on its
own subnetwork, set the subnet mask to 255.255.255.0 for the
devices on that subnetwork.
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 whose IP address’s first octet
matches the sender’s IP address’s first
octet.
255.255.0.0 IP packets are only transmitted to
devices whose IP address’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 whose IP address’s first three
octets match the sender’s IP address’s