Edit

Supporting NVGRE in UDP Segmentation Offload (USO)

  • Article

NDIS 6.85 introduces Network Virtualization using Generic Routing Encapsulation (NVGRE) with UDP segmentation offload (USO). NDIS miniport, protocol, and filter drivers, as well as NICs that perform USO, should support NVGRE and VXLAN encapsulations.

Note: This article presumes you're familiar with the information in UDP Segmentation Offload (USO).

If NDIS_TCP_SEND_OFFLOADS_SUPPLEMENTAL_NET_BUFFER_LIST_INFO.IsEncapsulatedPacket is TRUE and the UdpSegmentationOffloadInfo out-of-band (OOB) information is valid, NVGRE and VXLAN support is required. The NIC must perform USO offload on the NVGRE/VXLAN-encapsulated packet with the following condition:

To support NVGRE in USO, protocol and filter drivers must:

NICs and miniport drivers may use the InnerFrameOffset, TransportIpHeaderRelativeOffset, and TcpHeaderRelativeOffset values provided in the NDIS_TCP_SEND_OFFLOADS_SUPPLEMENTAL_NET_BUFFER_LIST_INFO structure. The NIC or miniport driver may perform any needed header checks on the tunnel (outer) IP header or subsequent headers to validate these offsets.

Miniport drivers must handle the case where NDIS_TCP_SEND_OFFLOADS_SUPPLEMENTAL_NET_BUFFER_LIST_INFO.InnerFrameOffset may be in a different scatter-gather list than the beginning of the packet. The protocol driver will guarantee that all the prepended encapsulation headers (ETH, IP, GRE/VXLAN) will be physically contiguous and will be in the first MDL of the packet.

Protocol and filter drivers don't ensure that the total UDP payload length is an exact multiple of the reduced MSS value when UdpSegmentation.SubMssFinalSegmentSupported is set in the NDIS_OFFLOAD capabilities. For this reason, miniport drivers and NICs with SubMssFinalSegmentSupported must update the tunnel (outer) IP header. NICs must generate as many full-sized segments as possible based on the reduced MSS value in the NDIS_UDP_SEGMENTATION_OFFLOAD_NET_BUFFER_LIST_INFO.Transmit OOB information. Only one sub-MSS segment may be generated per LSOv2 send.

Miniport drivers must:

  • Compute the checksum for the tunnel (outer) IP header.
  • Increment the IP identification (IP ID) value of the tunnel (outer) IP header for every packet. The first packet must use the IP ID in the original tunnel (outer) IP header.
  • Increment the IP ID of the transport (inner) IP header for every packet. The first packet must use the IP ID in the original transport (inner) IP header.
  • Compute the checksum for the UDP header and the transport (inner) IP header.
  • Ensure that the complete headers, including the encapsulation tunnel (outer) headers are added to every generated packet.

UDP Segmentation Offload (USO)