ZyXEL GS-1524 Manuel d'utilisateur télécharger pdf (Page 158)

Appendix A IP Addresses and Subnetting

GS-1524/GS-1548 User’s Guide

158

The following figure shows the company network after subnetting. There are now

two sub-networks, A and B.

Figure 91 Subnetting Example: After Subnetting

In a 25-bit subnet the host ID has 7 bits, so each sub-network has a maximum of

– 2 or 126 possible hosts (a host ID of all zeroes is the subnet’s address itself,

all ones is the subnet’s broadcast address).

192.168.1.0 with mask 255.255.255.128 is subnet A itself, and 192.168.1.127

with mask 255.255.255.128 is its broadcast address. Therefore, the lowest IP

address that can be assigned to an actual host for subnet A is 192.168.1.1 and

the highest is 192.168.1.126.

Similarly, the host ID range for subnet B is 192.168.1.129 to 192.168.1.254.

Example: Four Subnets

The previous example illustrated using a 25-bit subnet mask to divide a 24-bit

address into two subnets. Similarly, to divide a 24-bit address into four subnets,

you need to “borrow” two host ID bits to give four possible combinations (00, 01,

10 and 11). The subnet mask is 26 bits

(11111111.11111111.11111111.11000000) or 255.255.255.192.

1 2 ... 153 154 155 156 157 158 159 160 161 162 163 ... 169 170

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ZyXEL GS-1524 Manuel d'utilisateur Page 158