ZyXEL P-335 Plus User Guide - Page 204

Example: Two Subnets

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P-335 Plus User's Guide Table 78 Alternative Subnet Mask Notation (continued) SUBNET MASK 255.255.255.240 255.255.255.248 255.255.255.252 SUBNET MASK "1" BITS /28 /29 /30 LAST OCTET BIT VALUE 1111 0000 1111 1000 1111 1100 DECIMAL 240 248 252 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 79 Two Subnets Example IP/SUBNET MASK IP Address IP Address (Binary) Subnet Mask Subnet Mask (Binary) NETWORK NUMBER 192.168.1. 11000000.10101000.00000001. 255.255.255. 11111111.11111111.11111111. HOST ID 0 00000000 0 00000000 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 80 Subnet 1 IP/SUBNET MASK IP Address IP Address (Binary) Subnet Mask Subnet Mask (Binary) 204 NETWORK NUMBER 192.168.1. 11000000.10101000.00000001. 255.255.255. 11111111.11111111.11111111. LAST OCTET BIT VALUE 0 00000000 128 10000000 Appendix D IP Addresses and Subnetting

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P-335 Plus User’s Guide
204
Appendix D IP Addresses and Subnetting
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 79
Two Subnets Example
NETWORK NUMBER
HOST ID
IP Address
192.168.1.
0
IP Address (Binary)
11000000.10101000.00000001.
00000000
Subnet Mask
255.255.255.
0
Subnet Mask (Binary)
11111111.11111111.11111111.
00000000
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.
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 78
Alternative Subnet Mask Notation (continued)
SUBNET MASK
SUBNET MASK “1” BITS
LAST OCTET BIT VALUE
DECIMAL
Table 80
Subnet 1
IP/SUBNET MASK
NETWORK NUMBER
LAST OCTET BIT
VALUE
IP Address
192.168.1.
0
IP Address (Binary)
11000000.10101000.00000001.
0
0000000
Subnet Mask
255.255.255.
128
Subnet Mask (Binary)
11111111.11111111.11111111.
1
0000000