Checksum offload

When packets are sent or received over OSA, TCP/IP supports offloading most IPv4 and IPv6 inbound and outbound checksum processing (IP header, TCP, and UDP checksums) to the OSA adapter. This is the default behavior.

The TCP/IP stack performs checksum processing in the following cases in which checksum processing cannot be offloaded:

• When data is transmitted that qualifies for TCP segmentation offload (when enabled).
• IPSec-encapsulated packets
• Fragmented and reassembled packets
• Outbound multicast and broadcast packets
• Outbound TCP packets that contain only a TCP header
• IPv6 packets that contain extension headers
• When multipath is in effect (unless all interfaces in the multipath group support checksum offload)

In some cases, you might want to use the NOCHECKSUMOFFLOAD parameter on the IPCONFIG and IPCONFIG6 profile statements to configure the TCP/IP stack to perform all checksum processing.