Bad IP Checksum
Checksums and Cyclic Redundancy Checks (CRCs) are methods used to verify the integrity of data by computing extra bits based on the data to be verified and transmitting them along with that data. The receiver applies the same algorithm to regenerate the extra information. If both ends derive the same set of information based on the date, it is assumed the data sent was in fact sent correctly.
Different areas of a packet may be subject to data verification CRCs. The entire packet (as a whole) is subject to a MAC level CRC done by the sending network interface card, and reviewed and removed (if found correct) by the receiving interface card.
A bad IP checksum differs from a bad MAC level checksum in that the packet generated by the network interface appears to be correct, but the IP protocol section of the packet is corrupt. A MAC layer checksum will result in the packet being discarded at the interface card level, where a packet containing a bad IP checksum will be processed by the stack and passed up to the associated IP application.
Possible reasons for the event:
A failing network adapter at the source.
A failing cable or connector along the route (this would typically also product a bad MAC layer checksum).
Bad TCP/IP drivers or protocol processing software at the source.
Translation software (NAT, software based firewall, software based router) is failing or malfunctioning.