11.3 UDP Checksum | TCP/IP Illustrated, Vol. 1: The Protocols (Addison-Wesley Professional Computing Series)
Synopsys IP Technical Bulletin: IP and TCP/UDP Checksum Offload Functionality and its Support in Synopsys' DesignWare Ethernet MAC 10/100/1000 - Universal Core
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Learning by practicing: Calculating the TCP Checksum, with a taste of scapy + Wireshark