Editing Transmission Control Protocol (section)

===Checksum offload {{anchor|checksum offload}}===
Many TCP/IP software stack implementations provide options to use hardware assistance to automatically compute the checksum in the [[network adapter]] prior to transmission onto the network or upon reception from the network for validation. This may reduce CPU load associated with calculating the checksum, potentially increasing overall network performance.

This feature may cause [[packet analyzer]]s that are unaware or uncertain about the use of checksum offload to report invalid checksums in outbound packets that have not yet reached the network adapter.<ref>{{cite web|url=https://wiki.wireshark.org/CaptureSetup/Offloading|title=Wireshark: Offloading|quote=Wireshark captures packets before they are sent to the network adapter. It won't see the correct checksum because it has not been calculated yet. Even worse, most OSes don't bother initialize this data so you're probably seeing little chunks of memory that you shouldn't. New installations of Wireshark 1.2 and above disable IP, TCP, and UDP checksum validation by default. You can disable checksum validation in each of those dissectors by hand if needed.|access-date=2017-02-24|archive-date=2017-01-31|archive-url=https://web.archive.org/web/20170131220028/https://wiki.wireshark.org/CaptureSetup/Offloading/|url-status=live}}</ref> This will only occur for packets that are intercepted before being transmitted by the network adapter; all packets transmitted by the network adaptor on the wire will have valid checksums.<ref>{{cite web|url=https://www.wireshark.org/docs/wsug_html_chunked/ChAdvChecksums.html|title=Wireshark: Checksums|quote=Checksum offloading often causes confusion as the network packets to be transmitted are handed over to Wireshark before the checksums are actually calculated. Wireshark gets these "empty" checksums and displays them as invalid, even though the packets will contain valid checksums when they leave the network hardware later.|access-date=2017-02-24|archive-date=2016-10-22|archive-url=https://web.archive.org/web/20161022133751/https://www.wireshark.org/docs/wsug_html_chunked/ChAdvChecksums.html|url-status=live}}</ref> This issue can also occur when monitoring packets being transmitted between virtual machines on the same host, where a virtual device driver may omit the checksum calculation (as an optimization), knowing that the checksum will be calculated later by the VM host kernel or its physical hardware.<!--[[User:Kvng/RTH]]-->