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:
11000101 10111101 this binary number is 50621 decimal (base 10)
01110110 10010101 this binary number is 30357 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 11000101 10111101 and 01110110 10010101 = 00111100 01010011
2. The internet checksum is the one's complement of the sum: 00111100 01010011 = 11000011 10101100
That's incorrect
That's correct
The answer was: 00111100 01010011
The answer was: 11000011 10101100