ZyXEL Communications VMG1312-B Series - Page 322

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