Computing an Internet checksum
Consider the two 16-bit words (shown in binary) below. Recall that to compute the Internet checksum of a set of 16-bit words, we compute the one's complement sum [1] of the two words. That is, we add the two numbers together, making sure that any carry into the 17th bit of this initial sum is added back into the 1's place of the resulting sum); we then take the one's complement of the result. Compute the Internet checksum value for these two 16-bit words:
10111001 10110101 this binary number is 47541 decimal (base 10)
01011100 01000110 this binary number is 23622 decimal (base 10)
Question List
1. What is the sum of these two 16 bit numbers? Don't put any spaces in your answer
2. Using the sum from question 1, what is the checksum? Don't put any spaces in your answer
Solution
1. The sum of 10111001 10110101 and 01011100 01000110 = 00010101 11111100
2. The internet checksum is the one's complement of the sum: 00010101 11111100 = 11101010 00000011
That's incorrect
That's correct
The answer was: 00010101 11111100
The answer was: 11101010 00000011