Subnet Masks; Table 85 Allowed Ip Address Range By Class; Table 86 "Natural" Masks - ZyXEL Communications PRESTIGE 2602R Series User Manual

Prestige 2602R Series User's Guide
Note: 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.
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.

Table 85 Allowed IP Address Range By Class

CLASS
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 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.
Table 86
293
ALLOWED RANGE OF FIRST OCTET
(BINARY)
00000000 to 01111111
10000000 to 10111111
11000000 to 11011111
11100000 to 11101111
"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
(DECIMAL)
0 to 127
128 to 191
192 to 223
224 to 239
NATURAL MASK
255.0.0.0
255.255.0.0
255.255.255.0
Appendix C IP Subnetting