Black Box LR5100A-T - Manual (Page 27)

Applications
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The router allows mask sizes from 8 to 32 bits. The subnet mask size determines how many
bits of the host field of the original IP network address will be used for the creation of
subnets. In this example, specifying a mask size of 26 will produce a subnet size of 2 bits.
Two bits gives 4 possible sub-network addresses from the original IP network address. Two
of the resulting sub-networks will have either all zeros or all ones as the subnet address;
these addresses are reserved for network functions and hence are invalid addresses. The
subnet mask for the above example networks will be 255.255.255.192:
So setting a subnet mask size of 26 will generate two sub-networks with up to 62 host
addresses each (64 potential addresses minus the all zero and all one addresses). The new IP
sub-network addresses will be: 199.169.100.64 and 199.169.100.128.
Figure 2 -2 Defining an IP Subnet Mask
1. IP Address
Location: Main
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Configuration
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LAN Set up
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LAN IP Set up
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IP Address / Size of Subnet Mask
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Original IP Network Address 199.169.100.0
Subnet IP Network Address
199.169.100.64
Subnet Mask Size 26
Router IP Address
199.169.100.65
Host IP Address
199.169.100.66 Host IP Address
199.169.100.67 Host IP Address
199.169.100.130 Host IP Address
199.169.100.131
Router IP Address
199.169.100.129
Subnet IP Network Address
199.169.100.128
Subnet Mask Size 26
Subnet Mask is
255.255.255.192
IP Computers IP Computers
LAN #1 LAN #2