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:
10100100 00100101 this binary number is 42021 decimal (base 10)
10111111 01010011 this binary number is 48979 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 10100100 00100101 and 10111111 01010011 = 01100011 01111001
2. The internet checksum is the one's complement of the sum: 01100011 01111001 = 10011100 10000110
That's incorrect
That's correct
The answer was: 01100011 01111001
The answer was: 10011100 10000110