236 Chapter 5: Network Protocols
Classes of Networks
Class A, B, and C networks provide three network sizes. By definition, all addresses in the same
network have the same numeric value network portion of the addresses. The rest of the address
is called the host portion of the address. Individual addresses in the same network all have a
different value in the host parts of the addresses but have identical values in the network part.
Class A networks have a 1-byte-long network part. That leaves 24 bits for the rest of the address,
or the host part. That means that 2
24
addresses are numerically possible in a Class A network.
Similarly, Class B networks have a 2-byte-long network part, leaving 16 bits for the host portion
Subnetting
The process of subdividing networks into smaller subnets. This is
jargon--for example, "Are you subnetting your network?"
Network mask
A 32-bit number, usually written in dotted decimal form. The mask is
used by computers to calculate the network number of a given IP
address by performing a Boolean AND of the address and mask. The
mask also defines the number of host bits in an address.
Mask
A generic term for a mask, whether it is a default mask or a subnet
mask.
Address mask
Another term for a mask.
Default Class A mask
The mask used for Class A networks when no subnetting is used. The
value is 255.0.0.0.
Default Class B mask
The mask used for Class B networks when no subnetting is used. The
value is 255.255.0.0.
Default Class C mask
The mask used for Class C networks when no subnetting is used. The
value is 255.255.255.0.
Subnet mask
A non-default mask used when subnetting.
Network part or network
field
Term used to describe the first part of an IP address. The network part is
8, 16, or 24 bits for Class A, B, and C networks, respectively.
Host part or host field
Term used to describe the last part of an IP address. The host part is 24,
16, or 8 bits for Class A, B, and C networks, respectively, when
subnetting is not used. When subnetting, the size of the host part
depends on the subnet mask chosen for that network.
Subnet part of subnet field
Term used to describe the middle part of an IP address. The subnet part
is variable in size, based on how subnetting is implemented.
Table 5-8
IP Addressing Terminology (Continued)
Term
Definition
ch05.fm Page 236 Monday, March 20, 2000 5:06 PM