ZyXEL Communications Vantage CNM 2.0 User Manual page 225

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.)
IP ADDRESS:
Class A 0 Network number
Class B 10 Network number
Class C 110 Network number
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
Since the first octet of a class "A" IP address must contain a "0", the first octet of a class "A" address can have
a value of 0 to 127.
Similarly the first octet of a class "B" must begin with "10", therefore the first octet of a class "B" address has a
valid range of 128 to 191. The first octet of a class "C" address begins with "110", and therefore has a range of
192 to 223.
CLASS ALLOWED RANGE OF FIRST OCTET
Class A 00000000 to 01111111
Class B 10000000 to 10111111
IP Subnetting
Classes of IP Addresses
OCTET 1 OCTET 2
Host ID
Network number
Network number
Host IDs of all zeros or all ones are not allowed.
24
–2 hosts (approximately 16 million hosts).
Allowed IP Address Range By Class
(BINARY)
Appendix D
IP Subnetting
OCTET 3
Host ID
Host ID
Network number
8
–2 or 254 hosts.
16
–2 or 65534 hosts.
ALLOWED RANGE OF FIRST OCTET
(DECIMAL)
0 to 127
128 to 191
Vantage CNM 2.0
OCTET 4
Host ID
Host ID
Host ID
O