== Checksum Calculation (source : wikipedia) ==

For example, use Hex 45000030442240008006442e8c7c19acae241e2b (20 bytes IP header):
  4500 + 0030 + 4422 + 4000 + 8006 + 0000 + 8c7c + 19ac + ae24 + 1e2b = 2BBCF [[BR]]
  2 + BBCF = BBD1 = 1011101111010001, the 1'S of sum = 0100010000101110 = 442E

To validate a header's checksum the same algorithm may be used - the checksum of the header with the checksum field filled in should be a word containing all zeros (value 0).

[wiki:Software/Firmware/Framework/R3_arch/ip Return ..]