Table 108 Two Subnets Example - ZyXEL Communications ES-2724 User Manual

ES-2724 User's Guide
Table 107 Alternative Subnet Mask Notation (continued)
SUBNET MASK
255.255.255.240
255.255.255.248
255.255.255.252
The first mask shown is the class "C" natural mask. Normally if no mask is specified it is
understood that the natural mask is being used.
Example: Two Subnets
As an example, you have a class "C" address 192.168.1.0 with subnet mask of 255.255.255.0.

Table 108 Two Subnets Example

IP/SUBNET MASK
IP Address
IP Address (Binary)
Subnet Mask
Subnet Mask (Binary)
The first three octets of the address make up the network number (class "C").
To make two networks, 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 make 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 109 Subnet 1
IP/SUBNET MASK
IP Address
IP Address (Binary)
Subnet Mask
Subnet Mask (Binary)
328
SUBNET MASK "1" BITS
/28
/29
/30
NETWORK NUMBER
192.168.1.
11000000.10101000.00000001.
255.255.255.
11111111.11111111.11111111.
NETWORK NUMBER
192.168.1.
11000000.10101000.00000001.
255.255.255.
11111111.11111111.11111111.
LAST OCTET BIT VALUE
1111 0000
1111 1000
1111 1100
HOST ID
0
00000000
0
00000000
LAST OCTET BIT
VALUE
0
00000000
128
10000000
Appendix B IP Addresses and Subnetting
DECIMAL
240
248
252