ZyXEL NBG-418N User Guide - Page 150

Subnetting

Page 150 highlights

Appendix A IP Addresses and Subnetting Table 62 Alternative Subnet Mask Notation (continued) SUBNET MASK ALTERNATIVE LAST OCTET LAST OCTET NOTATION (BINARY) (DECIMAL) 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 Subnetting You can use subnetting to divide one network into multiple sub-networks. In the following example a network administrator creates two sub-networks to isolate a group of servers from the rest of the company network for security reasons. In this example, the company network address is 192.168.1.0. The first three octets of the address (192.168.1) are the network number, and the remaining octet is the host ID, allowing a maximum of 28 - 2 or 254 possible hosts. The following figure shows the company network before subnetting. Figure 109 Subnetting Example: Before Subnetting You can "borrow" one of the host ID bits to divide the network 192.168.1.0 into two separate subnetworks. The subnet mask is now 25 bits (255.255.255.128 or /25). The "borrowed" host ID bit can have a value of either 0 or 1, allowing two subnets; 192.168.1.0 /25 and 192.168.1.128 /25. The following figure shows the company network after subnetting. There are now two subnetworks, A and B. 150 NBG-418N User's Guide

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Appendix A IP Addresses and Subnetting
NBG-418N User’s Guide
150
Subnetting
You can use subnetting to divide one network into multiple sub-networks. In the following example
a network administrator creates two sub-networks to isolate a group of servers from the rest of the
company network for security reasons.
In this example, the company network address is 192.168.1.0. The first three octets of the address
(192.168.1) are the network number, and the remaining octet is the host ID, allowing a maximum
of 2
8
– 2 or 254 possible hosts.
The following figure shows the company network before subnetting.
Figure 109
Subnetting Example: Before Subnetting
You can “borrow” one of the host ID bits to divide the network 192.168.1.0 into two separate sub-
networks. The subnet mask is now 25 bits (255.255.255.128 or /25).
The “borrowed” host ID bit can have a value of either 0 or 1, allowing two subnets; 192.168.1.0 /25
and 192.168.1.128 /25.
The following figure shows the company network after subnetting. There are now two sub-
networks,
A
and
B
.
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
Table 62
Alternative Subnet Mask Notation (continued)
SUBNET MASK
ALTERNATIVE
NOTATION
LAST OCTET
(BINARY)
LAST OCTET
(DECIMAL)