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:
01111100 01011110 this binary number is 31838 decimal (base 10)
01110011 11111001 this binary number is 29689 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 01111100 01011110 and 01110011 11111001 = 11110000 01010111
2. The internet checksum is the one's complement of the sum: 11110000 01010111 = 00001111 10101000
That's incorrect
That's correct
The answer was: 11110000 01010111
The answer was: 00001111 10101000