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VigorSwitch G2240 User’s Guide 18
In this diagram, you can see the subnet mask with 25-bit long, 255.255.255.128, contains
126 members in the sub-netted network. Another is that the length of network prefix equals
the number of the bit with 1s in that subnet mask. With this, you can easily count the
number of IP addresses matched. The following table shows the result.
Prefix Length No. of IP matched No. of Addressable IP
/32 1 -
/31 2 -
/30 4 2
/29 8 6
/28 16 14
/27 32 30
/26 64 62
/25 128 126
/24 256 254
/23 512 510
/22 1024 1022
/21 2048 2046
/20 4096 4094
/19 8192 8190
/18 16384 16382
/17 32768 32766
/16 65536 65534
According to the scheme above, a subnet mask 255.255.255.0 will partition a network with
the class C. It means there will have a maximum of 254 effective nodes existed in this
sub-netted network and is considered a physical network in an autonomous network. So it
owns a network IP address which may looks like 168.1.2.0.
With the subnet mask, a bigger network can be cut into small pieces of network. If we want
to have more than two independent networks in a worknet, a partition to the network must
be performed. In this case, subnet mask must be applied.
For different network applications, the subnet mask may look like 255.255.255.240. This
means it is a small network accommodating a maximum of 15 nodes in the network.
Default gateway:
For the routed packet, if the destination is not in the routing table, all the traffic is put into
the device with the designated IP address, known as default router. Basically, it is a routing
policy. The gateway setting is used for Trap Events Host only in the switch.
For assigning an IP address to the switch, you just have to check what the IP address of the
network will be connected with the switch. Use the same network address and append your
host address to it.