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replaced https://tools.ietf.org/html/rfc with https://www.rfc-editor.org/rfc/rfc
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To strictly answer the questions:

  • Can the checksum itself be corrupted? Certainly, the noise sources have no idea whether they are corrupting data bits or checksum bits
  • What happens if only the checksum itself is corrupted? The calculated value by the receiver is certain to fail the match.
  • If checksum and data are corrupted, t(as given in the first answer) it's very unlikely to match.

While checksums in general have the characteristic that there are many messages which identical checksums (after all, we're going from perhaps 1Kbyte packet to 16 bits), many real life checksums have surprising good and bad properties. For example, IP checksum is guaranteed to detect all 1-bit errors; but fails to detect byte swaps. Real communications lines have certain errors much more common than others: much more common to get "all bits arrive as 0" for a short period for example, and "bytes are swapped" is more or less impossible.

For a deeper understanding

Hope that's helpful

Jonathan.

To strictly answer the questions:

  • Can the checksum itself be corrupted? Certainly, the noise sources have no idea whether they are corrupting data bits or checksum bits
  • What happens if only the checksum itself is corrupted? The calculated value by the receiver is certain to fail the match.
  • If checksum and data are corrupted, t(as given in the first answer) it's very unlikely to match.

While checksums in general have the characteristic that there are many messages which identical checksums (after all, we're going from perhaps 1Kbyte packet to 16 bits), many real life checksums have surprising good and bad properties. For example, IP checksum is guaranteed to detect all 1-bit errors; but fails to detect byte swaps. Real communications lines have certain errors much more common than others: much more common to get "all bits arrive as 0" for a short period for example, and "bytes are swapped" is more or less impossible.

For a deeper understanding

Hope that's helpful

Jonathan.

To strictly answer the questions:

  • Can the checksum itself be corrupted? Certainly, the noise sources have no idea whether they are corrupting data bits or checksum bits
  • What happens if only the checksum itself is corrupted? The calculated value by the receiver is certain to fail the match.
  • If checksum and data are corrupted, t(as given in the first answer) it's very unlikely to match.

While checksums in general have the characteristic that there are many messages which identical checksums (after all, we're going from perhaps 1Kbyte packet to 16 bits), many real life checksums have surprising good and bad properties. For example, IP checksum is guaranteed to detect all 1-bit errors; but fails to detect byte swaps. Real communications lines have certain errors much more common than others: much more common to get "all bits arrive as 0" for a short period for example, and "bytes are swapped" is more or less impossible.

For a deeper understanding

Hope that's helpful

Jonathan.

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jonathanjo
jonathanjo
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To strictly answer the questions:

  • Can the checksum itself be corrupted? Certainly, the noise sources have no idea whether they are corrupting data bits or checksum bits
  • What happens if only the checksum itself is corrupted? The calculated value by the receiver is certain to fail the match.
  • If checksum and data are corrupted, t(as given in the first answer) it's very unlikely to match.

While checksums in general have the characteristic that there are many messages which identical checksums (after all, we're going from perhaps 1Kbyte packet to 16 bits), many real life checksums have surprising good and bad properties. For example, IP checksum is guaranteed to detect all 1-bit errors; but fails to detect byte swaps. Real communications lines have certain errors much more common than others: much more common to get "all bits arrive as 0" for a short period for example, and "bytes are swapped" is more or less impossible.

For a deeper understanding

Hope that's helpful

Jonathan.