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:
01010001 00000010 this binary number is 20738 decimal (base 10)
11000111 01101111 this binary number is 51055 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 01010001 00000010 and 11000111 01101111 = 00011000 01110010
2. The internet checksum is the one's complement of the sum: 00011000 01110010 = 11100111 10001101
That's incorrect
That's correct
The answer was: 00011000 01110010
The answer was: 11100111 10001101