IPv4_header_checksum
Internet checksum
Mechanism to detect corruption in the header of an IPv4 packet
The Internet checksum,[1][2] also called the IPv4 header checksum is a checksum used in version 4 of the Internet Protocol (IPv4) to detect corruption in the header of IPv4 packets. It is carried in the IP packet header, and represents the 16-bit result of summation of the header words.[3]
The IPv6 protocol does not use header checksums. Its designers considered that the whole-packet link layer checksumming provided in protocols, such as PPP and Ethernet, combined with the use of checksums in upper layer protocols such as TCP and UDP, are sufficient.[4] Thus, IPv6 routers are relieved of the task of recomputing the checksum whenever the packet changes, for instance by the lowering of the Hop limit counter on every hop.
The Internet checksum is mandatory to detect errors in IPv6 UDP packets (including data payload).
The Internet checksum is used to detect errors in ICMP packets (including data payload).