Information Technology Reference
In-Depth Information
fore, the an s wer is 00011010. You might think this method involve s too much guesswork,
but it becomes second nature after some practice.
The number is larger than 128; enable that bit. [1???????]
How far is 137 from 128: 9; enable the remaining bits for a value of 9 [1???1001].
The answer is 10001001.
Conversion Example C-17
Convert 137 to Binary
The number is larger than 128; enable that bit. [1???????]
Because 211-128 is greater than 64, enable that bit. [11??????] (Remember that
11000000 = 192.)
Because 211-192=19, enable bits 16, 2, and 1. [11?1??11]
The answer is 11010011.
Conversion Example C-18
Convert 211 to Binary
In addition to remembering the bit-position values (128, 64, 32, 16, 8, 4, 2, 1), it helps to
remember network subnet mask values. Remembering them makes it easier to figure out
whether you need to enable a bit. Table C-6 summarizes the binary subnet mask numbers
and their decimal values.
Ta b l e C - 6
Binary Masks and Their Decimal Values
Binary Mask
Decimal
10000000
128
11000000
192
11100000
224
11110000
240
11111000
248
11111100
252
11111110
254
References and Recommended Readings
ISO/IEC 7498-1: 1994. “Information Processing Systems - OSI Reference Model - The Ba-
sic Model.”
RFC 791, Internet Protocol.
www.ietf.org/rfc.
RFC 793, Transmission Control Protocol.
www.ietf.org/rfc.
