ZyXEL G-405 User Guide - Page 85

IP Subnetting

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ZyAIR G-405 User's Guide 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 8-1 Classes of IP Addresses IP ADDRESS: Class A 0 Class B 10 Class C 110 OCTET 1 Network number Network number Network number OCTET 2 Host ID Network number Network number OCTET 3 Host ID Host ID Network number OCTET 4 Host ID Host ID Host ID Host IDs of all zeros or all ones are not allowed. Therefore: A class "C" network (8 host bits) can have 28 -2 or 254 hosts. A class "B" address (16 host bits) can have 216 -2 or 65534 hosts. A class "A" address (24 host bits) can have 224 -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. IP Subnetting K

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ZyAIR G-405 User’s Guide
IP Subnetting
K
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.
¾
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.
¾
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.
¾
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.
¾
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 8-1 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:
¾
A class “C” network (8 host bits) can have 2
8
–2 or 254 hosts.
¾
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.