3Com CoreBuilder 3500, Implementation Manual, Page: 266 / 592

266 C
HAPTER
11: I
NTERNET
P
ROTOCOL
(IP)
Figure 44
Subnet Masking
Figure 45 shows an example of an IP address that includes network,
subnet, and host parts. Suppose the IP address is
158.101.230.52 with a
subnet mask of 255.255.255.0 . Since this is a Class B address, this
address is divided as follows:
■
158.101 is the network part
■
230 is the subnet part
■
52
is the host part
As shown in this example, the 32 bits of an IP address and subnet mask
are usually written using an integer shorthand. This notation translates
four consecutive 8-bit groups, octets, into four integers that range from 0
through 255. The subnet mask in the example is written as
255.255.255.0.
Traditionally, subnet masks were applied to octets in their entirety.
However, one octet in the subnet mask can be further subdivided so that
part of the octet indicates an
extension
of the network number, and the
rest of the same octet indicates the host number, as shown in Figure 45.
IP address
Network Subnet and Host
Subnet mask
networ Host subn
Subnet
Network
Apply the subnet mask
Result = subnet/host boundary
Take the IP address
1 0 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1