User's Manual

Appendix A IP Addresses and Subnetting
B222s User’s Guide
180
The following figure shows an exam ple I P address in which t he first t hree oct et s ( 192.168.1) are
the network num ber, and t he fourth octet ( 16) is t he host I D.
Figure 101 Net work Num ber and Host I D
How m uch of the I P address is t he network num ber and how m uch is t he host I D var ies according
to t he subnet m ask.
Subnet Masks
A subnet m ask is used t o det erm ine w hich bit s are part of t he net work num ber, and which bits are
par t of t he host I D (using a logical AND operation) . The term “ subnet ” is short for “ sub- net work”.
A subnet m ask has 32 bits. I f a bit in t he subnet m ask is a “ 1” t hen the corresponding bit in t he I P
address is part of t he net work num ber. I f a bit in the subnet m ask is “ 0” t hen t he corresponding bit
in the I P address is part of t he host I D.
The following exam ple shows a subnet m ask identifying the network num ber ( in bold t ext ) and host
I D of an I P address ( 192.168.1.2 in decim al) .
By convent ion, subnet m asks always consist of a continuous sequence of ones beginning from t he
leftm ost bit of t he m ask, followed by a continuous sequence of zeros, for a t otal num ber of 32 bits.
Table 74 I P Address Net work Num ber and Host I D Exam ple
1ST OCTET:
(192)
2ND
OCTET:
(168)
3RD
OCTET:
(1)
4TH OCTET
(2)
I P Address ( Binary) 11000000 10101000 00000001 00000010
Subnet Mask ( Binary) 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 00000000
Net work Num ber 1 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 1
Host I D 00000010