Filter
Top Products
Dimension ES-2008 Ethernet Switch
L IP Subnetting
Appendix B
IP Subnetting
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.)
Chart 1 Classes of IP Addresses
IP ADDRESS: OCTET 1 OCTET 2 OCTET 3 OCTET 4
Class A 0 Network number Host ID Host ID Host ID
Class B 10 Network number Network number Host ID Host ID
Class C 110 Network number Network number Network number Host ID
Host IDs of all zeros or all ones are not allowed.
Therefore:
A class “C” network (8 host bits) can have 2
8
–2 or 254 hosts.
A class “B” address (16 host bits) can have 2
16
–2 or 65534 hosts.
A class “A” address (24 host bits) can have 2
24
–2 hosts (approximately 16 million hosts).
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.