Ip Subnetting - ZyXEL Communications Dimension ES-2008 User Manual

Dimension ES-2008 Ethernet Switch
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
Class B 10
Class C 110
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
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.
L
Chart 1 Classes of IP Addresses
OCTET 1
Network number
Network number
Network number

IP Subnetting

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