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Checksum field in TCP header is

  1. ones complement of sum of header and data in bytes
  2. ones complement of sum of header, data and pseudo header in $16$ bit words
  3. dropped from $\text{IPv6}$ header format
  4. better than $\text{md5}$ or $\text{sh1}$ methods
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IPv6 does not have checksum field so c may be answer
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Option B and C both are true.
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No, IPv6 has dropped it's own checksum (at Network Layer). It can't drop TCP's checksum (at Transport Layer)

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4 Answers

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1 vote
$\underline{\mathbf{Answer:}\Rightarrow}\;\mathbf{b.}$

In the TCP header checksum calculation includes the header, data, and pseudo-header.

All these values are added and stored in one’s complement form.
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Option B) is correct


Source: Tanenbaum

 

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Options B and C both are true.

Explanation:

  1. In the TCP header checksum calculation includes the header, data, and pseudo-header. All these values are added and stored in one’s complement form.
  2. Higher layer (>=4) protocols like TCP and UDP still have their own checksums. So many lower-layer protocols (<=2) already have their own checksums that having another checksum in IP (layer 3) was seen as unnecessary overhead. Answer is mentioned in stackoverflow .Please refer https://stackoverflow.com/questions/54074898/ipv4-header-included-checksum-but-not-in-ipv6-why
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For TCP; the sum of header, data and psuedoheader is taken, in 16-bit or 2 Byte words.

Then it's 1's complement is calculated (1's complement $\equiv$ negation) and stored in the checksum field.

Hence, when we add up all the numbers, we'd get $0$

 

Option B is correct.

Bonus

What is Psuedoheader in TCP?

 

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Answer:

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