Header Checksum

Ones-complement checksum over the header only, not the payload.

Reading a capture

Recomputed at every hop, because TTL changes. Covers the header alone — payload integrity is someone else's problem, which is part of why TCP carries its own checksum.

Where it sits

IPv4 Datagram > Header Checksum

• Open in the explorer — TCP over IPv4, in a protected QoS Data frame, aggregated
• Open in the explorer — ICMP echo over IPv4, in a QoS Data frame
• Open in the explorer — TCP over IPv4, in a protected QoS Data frame
• Open in the explorer — TCP over IPv4, in an open QoS Data frame
• Open in the explorer — UDP over IPv4, in a QoS Data frame

Accuracy

Clause

RFC 791 §3.1

Byte order

big-endian — network byte order

Verified

Not verified against the standard. Treat this as a claim, not a fact.