Disabling Packet Checksum Validation

By default, the DNCA performs a checksum validation for each packet that is forwarded to it. In environments with network interface cards (NICs) that use large receive option (LRO) or checksum offloading (rx-checksumming) or both, checksum validation of captured network packets is managed in the hardware of the card. Since the checksum validation is performed on individual packets in the hardware, there is no reasonable must perform another checksum of the aggregated, larger packets.

When either or both of these options are enabled, the resulting packets that are forwarded to the DNCA do not contain a recomputed packet checksum, which causes the DNCA checksum to fail and the packet to be discarded. Other effects:

• The counts of missing or partial pages rise in session data.
• The DNCA stats must show a significant increase in Total checksum errors. See Stats per Instance.

As an alternative, you can enable packet checksum validation for the Unica Discover Network Capture Application if you disable checksum offloading through the operating system driver level. However, this option adds a processing usage to the operating system.

• The command to disable checksum offloading to the NIC must be placed in the bootup configuration script.