Ip Subnetting; Ip Addressing; Ip Classes; Table 83 Classes Of Ip Addresses - ZyXEL Communications ADSL2+ Ethernet/USB Gateway 660RU-Tx Series User Manual

IP Addressing

Routers "route" based on the network number. The router that delivers the data packet to the
correct destination host uses the host ID.

IP Classes

An IP address is made up of four octets (eight bits), written in dotted decimal notation, for
example, 192.168.1.1. IP addresses are categorized into different classes. The class of an
address depends on the value of its first octet.
• Class "A" addresses have a 0 in the left most bit. In a class "A" address the first octet is
the network number and the remaining three octets make up the host ID.
• Class "B" addresses have a 1 in the left most bit and a 0 in the next left most bit. In a class
"B" address the first two octets make up the network number and the two remaining
octets make up the host ID.
• Class "C" addresses begin (starting from the left) with 1 1 0. In a class "C" address the
first three octets make up the network number and the last octet is the host ID.
• Class "D" addresses begin with 1 1 1 0. Class "D" addresses are used for multicasting.
(There is also a class "E" address. It is reserved for future use.)

Table 83 Classes of IP Addresses

IP ADDRESS:
Class A
Class B
Class C
Note: Host IDs of all zeros or all ones are not allowed.
Therefore:
A class "C" network (8 host bits) can have 2
A class "B" address (16 host bits) can have 2
A class "A" address (24 host bits) can have 2
Appendix C
OCTET 1
0 Network number
10 Network number
110 Network number
Prestige 660RU-Tx Series User's Guide
Appendix C

IP Subnetting

OCTET 2 OCTET 3
Host ID Host ID
Network number Host ID
Network number Network number
8
–2 or 254 hosts.
16
–2 or 65534 hosts.
24
–2 hosts (approximately 16 million hosts).
OCTET 4
Host ID
Host ID
Host ID
260