Kamis, 04 Oktober 2012

Penghitungan Subnet Mask

Subnet Mask

Perhaps the most recognizable aspect of subnetting is the subnet mask. Like IP addresses, a subnet mask contains four bytes (32 bits) and is often written using the same "dotted-decimal" notation. For example, a very common subnet mask in its binary representation
    11111111 11111111 11111111 00000000
is typically shown in the equivalent, more readable form

Applying a Subnet Mask

A subnet mask neither works like an IP address, nor does it exist independently from them. Instead, subnet masks accompany an IP address and the two values work together. Applying the subnet mask to an IP address splits the address into two parts, an "extended network address" and a host address. For a subnet mask to be valid, its leftmost bits must be set to '1'. For example,
    00000000 00000000 00000000 00000000
is an invalid subnet mask because the leftmost bit is set to '0'. Conversely, the rightmost bits in a valid subnet mask must be set to '0', not '1'. Therefore,
    11111111 11111111 11111111 11111111
is invalid.

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