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:
01001111 01001001 this binary number is 20297 decimal (base 10)
11010111 10110111 this binary number is 55223 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 01001111 01001001 and 11010111 10110111 = 00100111 00000001
2. The internet checksum is the one's complement of the sum: 00100111 00000001 = 11011000 11111110
That's incorrect
That's correct
The answer was: 00100111 00000001
The answer was: 11011000 11111110