Chart H-2 Allowed Ip Address Range By Class; Chart H-3 "Natural" Masks - ZyXEL Communications VANTAGE RADIUS 50 User Manual

Vantage RADIUS User's Guide
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
Class B
Class C
Class D
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.
H-2

Chart H-2 Allowed IP Address Range By Class

(BINARY)
00000000 to 01111111
10000000 to 10111111
11000000 to 11011111
11100000 to 11101111

Chart H-3 "Natural" Masks

CLASS
A
B
C
8
–2 or 254 hosts.
16
–2 or 65534 hosts.
24
–2 hosts (approximately 16 million hosts).
ALLOWED RANGE OF FIRST OCTET
NATURAL MASK
255.0.0.0
255.255.0.0
255.255.255.0
(DECIMAL)
0 to 127
128 to 191
192 to 223
224 to 239
IP Subnetting