ZyXEL Communications VMG1312-B Series, Руководство пользователя

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Appendix B IP Addresses and Subnetting
VMG1312-B Series User’s Guide
320
The following figure shows an exam ple I P address in which t he first t hree oct et s ( 192.168.1) are
t he net w ork num ber, and t he fourt h oct et ( 16) is t he host I D.
Figure 181 Net work Num ber and Host I D
How m uch of t he I P address is t he net work num ber and how m uch is t he host I D varies according
t o t he subnet m ask.
Subnet Masks
A subnet m ask is used t o det erm ine which bit s are part of t he net work num ber, and which bit s are
part of t he host I D ( using a logical AND operat ion) . The t erm “ subnet ” is short for “ sub- net work”.
A subnet m ask has 32 bit s. I f a bit in t he subnet m ask is a “ 1” t hen t he corresponding bit in t he I P
address is part of t he net w ork num ber. I f a bit in t he subnet m ask is “ 0” t hen t he corresponding bit
in t he I P address is part of t he host I D.
The following exam ple shows a subnet m ask ident ifying t he net w ork 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 cont inuous sequence of ones beginning from t he
left m ost bit of t he m ask, followed by a cont inuous sequence of zeros, for a t ot al num ber of 32 bit s.
Table 111 Subnet Masks
1ST OCTET:
(192)
2ND
OCTET:
(168)
3RD
OCTET:
(1)
4TH OCTET
(2)
I P Addr ess ( Binar y) 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 w or k 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