Subnetwork Part; Network Part - 3Com CoreBuilder 2500 User Manual

Network Part

The location of the boundary between the network part and the host
part depends on the class that the central agency assigns to your
network. The three primary classes of IP addresses are A, B, and C:
Class A address — Uses 8 bits for the network part and 24 bits for
the host part. Although only a few Class A networks can be created,
each can contain a very large number of hosts.
Class B address — Uses 16 bits for the network part and 16 bits for
the host part.
Class C address — Uses 24 bits for the network part and 8 bits for
the host part. Each Class C network can contain only 254 hosts, but
many such networks can be created.
The high-order bits of the network part of the address designate the IP
network class.

Subnetwork Part

In some environments, the IP address contains a subnetwork part, at the
beginning of the host part of the IP address. Thus, you can divide a single
Class A, B, or C network internally, allowing the network to appear as a
single network to other networks. The subnetwork part of the IP address
is visible only to hosts and gateways on the subnetwork.
When an IP address contains a subnetwork part, a subnet mask identifies
the bits that constitute the subnetwork address and the bits that
constitute the host address. A subnet mask is a 32-bit number in the IP
address format. The 1 bits in the subnet mask indicate the network and
subnetwork part of the address. The 0 bits in the subnet mask indicate
the host part of the IP address. See Figure 4-3.
IP address
Subnet mask
1 1 1 1 1 1 1 1 1 1 1
Figure 4-3 How a Subnet Mask Is Applied to the IP Address
Take the IP address
Network
Apply the subnet mask
1 1 1 1 1 1 1 1 1 1 1 1 1
Result = subnet/host boundary
Network networ
Elements of IP Routing
Subnet and Host
0 0 0 0 0
Subnet
subn Host
4-3
0 0 0