User's Manual

Appendix A IP Addresses and Subnetting

B222s User’s Guide

182

The following t able shows som e possible subnet m asks using bot h notat ions.

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 network adm inistrat or cr eat es two sub- net works to isolat e a group of servers from the rest of the

com pany network for securit y reasons.

I n t his exam ple, t he com pany network addr ess is 192.168.1.0. The first three oct et s of the address

( 192.168.1) are the network num ber, and the rem aining oct et is the host I D, allowing a m axim um

of 2

– 2 or 254 possible host s.

The following figure shows t he com pany net work before subnet t ing.

Figure 102 Subnet ting Exam ple: Before Subnet t ing

You can “borrow” one of the host I D bit s t o divide t he net work 192.168.1.0 int o t wo separat e sub-

networks. 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 either 0 or 1, allowing t wo subnet s; 192.168.1.0 / 25

and 192.168.1.128 / 25.

Table 77 Alternat ive Subnet Mask Notat 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