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Network ID guidelines
Follow these guidelines when assigning a network ID:
(i) The network ID must be unique within the IP internetwork. If you plan to Chapter Three: Advanced Computer Networks
connect to the public Internet, it must be unique on the Internet. If you are not
connecting to the public Internet, the local network ID must be unique within
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your private internetwork.
(ii) The network ID cannot start with the number 127, as this number is reserved
for internal loopback functions in a class A address.
(iii) The network ID cannot have all bits set to 1, as this is reserved for the IP
broadcast address.
(iv) The network ID cannot have all bits set to 0, as this is used to indicate a specific
host on the local network and is not routed.

Class ranges of network IDs
Table 3.3: Class ranges of network ID

Address Class First Network ID Last Network ID
Class A 1.0.0.0 126.0.0.0

Class B 128.0.0.0 191.255.0.0
Class C 192.0.0.0 223.255.255.0

Host ID guidelines
The host ID serves to identify a TCP/IP host within a network, and when combined
with the IP network ID, it forms an IP address. Here are some guidelines to follow
when assigning a host ID:
(i) The host ID must be unique within the network ID.
(ii) It is not allowed to have all bits set to 1 within the host ID, as this is reserved
as a broadcast address used to send packets to all hosts on a network.
(iii) It is not permitted to have all bits set to 0 within the host ID, as this is reserved
to indicate the IP network ID.

Class ranges of host IDs

Table 3.4: Class ranges of host IDs
Address class First host ID Last host ID
Class A N.0.0.1 N.255.255.254
Class B N.N.0.1 N.N.255.254
Class C N.N.N.1 N.N.N.254

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Student’s Book Form Five

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