Classless Interdomain Routing - Cidr - D-Link DES-3326 User Manual

DES-3326 Layer 3 Fast Ethernet Switch User's Guide
00001010.00101010.11111111.11111111
Broadcast Address
This example uses a 3-bit subnet mask. (There are 3 additional
bits added to the default Class A subnet mask of 8 bits). So the
number of subnets is:
2 – 2 = 8 – 2 = 6
3
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 32 – 11 =
21 bits, so the total number of nodes is:
2 – 2 = 2,097,152 – 2 = 2,097,150
21
Multiplying the number of subnets times the number of nodes
gives 12,582,900 possible nodes. 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
The classed IP addressing scheme is somewhat wasteful of IP
address space. Medium-sized networks were assigned Class B
addresses (65533 nodes), and Class A IP addresses (over 16 million
nodes) were assigned to large networks. Even a small network was
given a Class C IP address that allowed 254 nodes. Most of these
assigned addresses were never used.
74
10.32.255.255
Switch Management and Operating Concepts