10.3 | The Mechanics of Subnetting | |||
10.3.6 | Calculating the resident subnetwork through ANDing |
Routers use subnet masks to determine the
home subnetwork for individual nodes. This process is referred to as
logical ANDing. ANDing is a binary process by which the router
calculates the subnetwork ID for an incoming packet.
ANDing is
similar to multiplication.
This process is handled at the binary level. Therefore, it is necessary to view the IP address and mask in binary. The IP address and the subnetwork address are ANDed with the result being the subnetwork ID. The router then uses that information to forward the packet across the correct interface. Subnetting is a learned skill. It will take many hours performing practice exercises to gain a development of flexible and workable schemes. A variety of subnet calculators are available on the web. However, a network administrator must know how to manually calculate subnets in order to effectively design the network scheme and assure the validity of the results from a subnet calculator. The subnet calculator will not provide the initial scheme, only the final addressing. Also, no calculators, of any kind, are permitted during the certification exam.
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