Table 88 Subnet 1; Table 89 Subnet 2 - ZyXEL Communications ADSL2+ Ethernet/USB Gateway 660RU-Tx Series User Manual

Prestige 660RU-Tx Series User's Guide
Divide the network 192.168.1.0 into two separate subnets by converting one of the host ID bits
of the IP address to a network number bit. The "borrowed" host ID bit can be either "0" or "1"
thus giving two subnets; 192.168.1.0 with mask 255.255.255.128 and 192.168.1.128 with
mask 255.255.255.128.
Note: In the following charts, shaded/bolded last octet bit values indicate host
ID bits "borrowed" to form network ID bits. The number of "borrowed" host ID
bits determines the number of subnets you can have. The remaining number
of host ID bits (after "borrowing") determines the number of hosts you can
have on each subnet.

Table 88 Subnet 1

IP Address
IP Address (Binary)
Subnet Mask
Subnet Mask (Binary)
Subnet Address: 192.168.1.0
Broadcast Address:
192.168.1.127

Table 89 Subnet 2

IP Address
IP Address (Binary)
Subnet Mask
Subnet Mask (Binary)
Subnet Address:
192.168.1.128
Broadcast Address:
192.168.1.255
The remaining 7 bits determine the number of hosts each subnet can have. Host IDs of all
zeros represent the subnet itself and host IDs of all ones are the broadcast address for that
subnet, so the actual number of hosts available on each subnet in the example above is 2
or 126 hosts for each subnet.
192.168.1.0 with mask 255.255.255.128 is the subnet itself, and 192.168.1.127 with mask
255.255.255.128 is the directed broadcast address for the first subnet. Therefore, the lowest IP
address that can be assigned to an actual host for the first subnet is 192.168.1.1 and the highest
is 192.168.1.126. Similarly the host ID range for the second subnet is 192.168.1.129 to
192.168.1.254.
263
NETWORK NUMBER
192.168.1.
11000000.10101000.00000001.
255.255.255.
11111111.11111111.11111111.
Lowest Host ID: 192.168.1.1
Highest Host ID: 192.168.1.126
NETWORK NUMBER
192.168.1.
11000000.10101000.00000001.
255.255.255.
11111111.11111111.11111111.
Lowest Host ID: 192.168.1.129
Highest Host ID: 192.168.1.254
LAST OCTET BIT
VALUE
0
00000000
128
10000000
LAST OCTET BIT VALUE
128
10000000
128
10000000
7
Appendix C
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