l2_len, l3_len, l4_len 등을 사용하는 라이브러리가 존재함

1. reassembly
2. Tx checksum offload

Reassembly

rte_ipv6_frag_reassemble_packet(), rte_ipv4_frag_reassemble_packet() Incoming mbuf should have its l2_len and l3_len fields setup correctly.

L4 checksum HW offloading

To use hardware L4 checksum offload, the user needs to

• fill l2_len and l3_len in mbuf
• set the flags PKT_TX_TCP_CKSUM, PKT_TX_SCTP_CKSUM or PKT_TX_UDP_CKSUM
• set the flag PKT_TX_IPV4 or PKT_TX_IPV6
• calculate the pseudo header checksum and set it in the L4 header (only for TCP or UDP). See rte_ipv4_phdr_cksum() and rte_ipv6_phdr_cksum(). For SCTP, set the crc field to 0.

L3 checksum HW offloading

• set the flag PKT_TX_IPV4 (IP checksum은 IPv4에만 존재)
• set the IP checksum field in the packet to 0
• fill the mbuf offload information: l2_len, l3_len
• PKT_TX_IP_CKSUM

IP checksum offloading

example from prog_guide/mbuf_lib.rst

This is supported on hardware advertising DEV_TX_OFFLOAD_IPV4_CKSUM.

mb->l2_len = len(out_eth)
mb->l3_len = len(out_ip)
mb->ol_flags |= PKT_TX_IPV4 | PKT_TX_IP_CSUM
set out_ip checksum to 0 in the packet

IP, UDP checksum offloading

This is supported on hardware advertising DEV_TX_OFFLOAD_IPV4_CKSUM and DEV_TX_OFFLOAD_UDP_CKSUM.

mb->l2_len = len(out_eth)
mb->l3_len = len(out_ip)
mb->ol_flags |= PKT_TX_IPV4 | PKT_TX_IP_CSUM | PKT_TX_UDP_CKSUM
set out_ip checksum to 0 in the packet
set out_udp checksum to pseudo header using rte_ipv4_phdr_cksum()

Outer IP, inner IP and inner TCP checksum offloading

This is supported on hardware advertising DEV_TX_OFFLOAD_IPV4_CKSUM, DEV_TX_OFFLOAD_UDP_CKSUM and DEV_TX_OFFLOAD_OUTER_IPV4_CKSUM.

mb->outer_l2_len = len(out_eth)
mb->outer_l3_len = len(out_ip)
mb->l2_len = len(out_udp + vxlan + in_eth)
mb->l3_len = len(in_ip)
mb->ol_flags |= PKT_TX_OUTER_IPV4 | PKT_TX_OUTER_IP_CKSUM  | \
  PKT_TX_IP_CKSUM |  PKT_TX_TCP_CKSUM;
set out_ip checksum to 0 in the packet
set in_ip checksum to 0 in the packet
set in_tcp checksum to pseudo header using rte_ipv4_phdr_cksum()