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address (such as a MAC address), the IP converted into a decimal number ranging
address functions at the network layer from 0 to 255, and the sections are separated
and is independent of the Data-Link by periods. This format, known as dotted
layer address. Every device and network decimal notation, is used to represent IP Chapter Three: Advanced Computer Networks
component that uses TCP/IP requires a addresses. For instance, the binary notation
FOR ONLINE READING ONLY
unique IP address. 11000000 10101000 00000011 00011000
corresponds to the dotted decimal notation
An IP address is akin to a street address,
designating a system’s location within 192.168.3.24.
the network. Just as a street address
must be unique to a particular house,
an IP address must be globally unique
and conform to a standardised format.
Each IP address comprises a network
ID and a host ID.

The network ID, also referred to as the Figure 3.17: Example of IPv4 address format
network address, identifies systems that
are part of the same physical network IP Address classes
defined by IP routers. All systems Initially, the Internet community introduced
within this network must have the five address classes (A, B, C, D, and E) to
same network ID, and this network cater to networks of varying sizes. Each
ID must be unique across the entire address class specifies the allocation of bits
internetwork. for the network ID and host ID, as well as

The host ID, or host address as shown the permissible number of networks and
in Figure 3.6, identifies individual hosts. TCP/IP supports class A, B, and C
workstations, servers, routers, or other addresses for assigning hosts, among the
TCP/IP hosts within a network. Each five classes established.
host’s address must be unique within
its respective network ID. The concept Class A
of network ID applies to any type of Class A addresses are designated for
IP network, regardless of whether it is networks needing a large number of hosts.
class-based, a subnet, or a supernet. In a Class A address, the highest-order bit
is set to zero. The next seven bits in the
32 bits
first octet form the network ID, while the
Net ID Host ID remaining 24 bits (the last three octets)
represent the host ID. This structure
Figure 3.16: IPv4 address format
permits 128 possible network IDs (0 to
An IP address is made up of 32 bits. To 127), but only 126 are usable (excluding 0
simplify working with these bits, the and 127), and up to 16,777,214 valid hosts
32-bit IP address is commonly divided per network. Class A addresses range from
into four 8-bit sections called octets, as 1.0.0.0 to 126.0.0.0 in decimal notation,
shown in Figure 3.17. Each octet is then with 127.0.0.0 reserved for loopback and

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Student’s Book Form Five

Computer Science Form 5.indd 153 23/07/2024 12:33