[dpdk-dev] Wrong TCP Checkum computed by hardware

[Padam Jeet Singh]

Hi,

While implementing a sample packet generation code, I am setting up the offload flags so that the hardware (82599ES in my case) computes the IP and TCP Checksums. However, it seems that only the IP checksum is computed whereas the TCP Checksum is computed, but computed wrong. Here is a snippet of what I doing:

/* First reset all offload flags */
mbuf->ol_flags = (uint16_t) (mbuf->ol_flags & (~PKT_TX_OFFLOAD_MASK));
/* Then enable IP Checksum offload */
mbuf->ol_flags |= PKT_TX_IP_CKSUM;
/* This is required to be set to 0 */
ipv4hdr->hdr_checksum = 0;
mbuf->ol_flags |= PKT_TX_TCP_CKSUM;
/* Compute the PSD header */
tcphdr->cksum = rte_ipv4_phdr_cksum(ipv4hdr);

When I replace the checksum computation from hardware-offload to a software implementation, the checksum computed is correct. I have verified both the cases with Wireshark on the system receiving the packets.

Any hint what could I be doing wrong here?

Thanks,
Padam