User`s guide

TCP/IP
C-7
SNMP and TCP/IP Concepts
internet address to a physical hardware address, and sends the
resulting frame directly to the destination.
If the information is sent between two devices on two different physi-
cal networks, however, the internet gateways form a cooperative,
interconnected structure. Datagrams pass from gateway to gateway
until they reach a gateway that can deliver them directly to a device
on that physical network.
Class A, B, and C Internet Addresses
TCP/IP defines a means for the network administrator to configure
the network that best suits the network environment at a site. One
method is to define the 32-bit TCP/IP network address in terms of the
number of networks and the number of hosts at the site. The network
address is partitioned into a network part and a host part.
There are 3 common partitions—Class A, Class B, and Class C. The
classification is done by the highest order bits. For example, a 0 in the
highest order bit of the 32-bit address indicates that the address is
Class A. Thus, the next 7 bits constitute the network address, and the
last 24 bits form the host address. The high order bits also constitute
the network mask for the Class A address.
The following table identifies the differences between Class A, B, and
C addresses.
Class Uses Highest
Order
Bits
(Binary)
Network
Address
Size
Host
Address
Size
Network Mask
(Hex)
A Sites with few
networks and
many hosts
0 7 bits 24 bits 0xFF000000
B Sites with some
networks and
some hosts
10 14 bits 16 bits 0xFFFF0000
C Sites with many
networks and
few hosts
110 21 bits 8 bits 0xFFFFFF00