ZyAIR B-4000 Hot Spot Gateway

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.

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.

Chart G-2 Allowed IP Address Range By Class

CLASS

ALLOWED RANGE OF FIRST OCTET

ALLOWED RANGE OF FIRST OCTET

 

(BINARY)

(DECIMAL)

 

 

 

Class A

00000000 to 01111111

0 to 127

 

 

 

Class B

10000000 to 10111111

128 to 191

 

 

 

Class C

11000000 to 11011111

192 to 223

 

 

 

Class D

11100000 to 11101111

224 to 239

 

 

 

Subnet Masks

A subnet mask is used to determine which bits are part of the network number, and which bits are part of the host ID (using a logical AND operation). A subnet mask has 32 bits; each bit of the mask corresponds to a bit of the IP address. If a bit in the subnet mask is a “1” then the corresponding bit in the IP address is part of the network number. If a bit in the subnet mask is “0” then the corresponding bit in the IP address is part of the host ID.

Subnet masks are expressed in dotted decimal notation just as IP addresses are. The “natural” masks for class A, B and C IP addresses are as follows.

Chart G-3 “Natural” Masks

CLASS

NATURAL MASK

 

 

A

255.0.0.0

 

 

B

255.255.0.0

 

 

C

255.255.255.0

 

 

Subnetting

With subnetting, the class arrangement of an IP address is ignored. For example, a class C address no longer has to have 24 bits of network number and 8 bits of host ID. With subnetting, some of the host ID bits are converted into network number bits. By convention, subnet masks always consist of a continuous

G-2

IP Subnetting