ZyXEL Communications VMG1312-B Series User Manual page 322

Appendix B IP Addresses and Subnetting
The following t able shows som e possible subnet m asks using bot h not at ions.
Table 114 Alt ernat ive Subnet Mask Not at ion
SUBNET MASK
255.255.255.0
255.255.255.128
255.255.255.192
255.255.255.224
255.255.255.240
255.255.255.248
255.255.255.252
Subnetting
You can use subnet t ing t o divide one net work int o m ult iple sub- net works. I n t he following exam ple
a net work adm inist rat or creat es t wo sub- net works t o isolat e a group of servers from t he rest of t he
com pany net work for securit y reasons.
I n t his exam ple, t he com pany net work address is 192.168.1.0. The first t hree oct et s of t he address
( 192.168.1) are t he net work num ber, and t he rem aining oct et is t he host I D, allowing a m axim um
8
of 2 – 2 or 254 possible host s.
The following figure shows t he com pany net work before subnet t ing.
Figure 182 Subnet t ing Exam ple: Before Subnet t ing
You can " borrow" one of t he host I D bit s t o divide t he net work 192.168.1.0 int o t wo separat e sub-
net works. The subnet m ask is now 25 bit s ( 255.255.255.128 or / 25) .
The " borrowed" host I D bit can have a value of eit her 0 or 1, allowing t wo subnet s; 192.168.1.0 / 25
and 192.168.1.128 / 25.
322
ALTERNATIVE LAST OCTET
NOTATION (BINARY)
/ 24 0000 0000
/ 25 1000 0000
/ 26 1100 0000
/ 27 1110 0000
/ 28 1111 0000
/ 29 1111 1000
/ 30 1111 1100
LAST OCTET
(DECIMAL)
0
128
192
224
240
248
252
VMG1312-B Series User's Guide