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11111111.11100000.00000000.00000000
Subnet Mask
00001010.00100000.00000000.00000000
Network Address
00001010.00101010.11111111.11111111
Broadcast Address
This example uses an 11-bit subnet mask. (There are 3
additional bits added to the default Class A subnet mask).
So the number of subnets is:
Subnets of all "0"s and all "1"s are not allowed, so 2 subnets
are subtracted from the total.
The number of bits used in the node part of the address is
24 – 3 = 21 bits, so the total number of nodes is:
21
2
– 2 = 2,097,152 – 2 = 2,097,150
Multiplying the number of subnets times the number of
nodes gives 12,582,900 possible nodes.
Note that this is less than the 16,777,214 possible nodes
that an unsubnetted class A network would have.
Subnetting reduces the number of possible nodes for a given
network, but increases the segmentation of the network.
Classless InterDomain Routing – CIDR
Under CIDR, the subnet mask notation is reduced to a
simplified shorthand. Instead of specifying all of the bits of
the subnet mask, it is simply listed as the number of
contiguous "1"s (bits) in the network portion of the address.
Look at the subnet mask of the above example in binary -
9033691-01
3
2
– 2 = 8 – 2 = 6
255.224.0.0
10.32.0.0
10.32.255.255
VH-2402-L3 Management Guide 141
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