When packets are sent or received over the OSA-Express feature
in QDIO mode, 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:
- IPv6 packets sent to and from OSA-Express features that support
only IPv4 checksum offload (OSA-Express3 and earlier features)
- Packets that go directly to another stack that shares the same
OSA-Express port when the OSA-Express feature does not support LPAR-to-LPAR
checksum offload (OSA-Express3 and earlier features)
- 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.