NDIS_UDP_SEGMENTATION_OFFLOAD structure (ntddndis.h)

  • Article

The NDIS_UDP_SEGMENTATION_OFFLOAD structure provides UDP Segmentation Offload (USO) information in the NDIS_OFFLOAD structure.

Syntax

typedef struct _NDIS_UDP_SEGMENTATION_OFFLOAD {
  struct {
    ULONG Encapsulation;
    ULONG MaxOffLoadSize;
    ULONG MinSegmentCount : 6;
    ULONG SubMssFinalSegmentSupported : 1;
#if ...
    ULONG Reserved : 25;
#else
    ULONG Reserved : 26;
#endif
  } IPv4;
  struct {
    ULONG Encapsulation;
    ULONG MaxOffLoadSize;
    ULONG MinSegmentCount : 6;
    ULONG SubMssFinalSegmentSupported : 1;
#if ...
    ULONG Reserved1 : 25;
#else
    ULONG Reserved1 : 26;
#endif
    ULONG IpExtensionHeadersSupported : 2;
    ULONG Reserved2 : 30;
  } IPv6;
} NDIS_UDP_SEGMENTATION_OFFLOAD, *PNDIS_UDP_SEGMENTATION_OFFLOAD;

Members

IPv4

A structure within NDIS_UDP_SEGMENTATION_OFFLOAD that specifies IPv4 information, containing the following members:

IPv4.Encapsulation

Encapsulation settings for IPv4. For more information about this member, see the following Remarks section.

IPv4.MaxOffLoadSize

The maximum bytes of user data that the transport can pass to the miniport driver in a single packet. The transport will not pass a packet to the miniport driver that contains more user data bytes than MaxOffLoadSize specifies. If such a packet must be transmitted, the transport itself segments the packet into smaller packets.

IPv4.MinSegmentCount

The minimum number of segments that a large UDP packet must be divisible by before the transport can offload it to the hardware for segmentation. The transport will not offload a large packet to the miniport driver for segmentation unless the miniport driver can create at least as many segments as MinSegmentCount specifies from the packet. If a large UDP packet does not meet the minimum-segment requirement, the TCP/IP transport itself segments the packet into smaller packets.

IPv4.SubMssFinalSegmentSupported

A ULONG value that specifies whether all segments that a miniport driver derives from a large UDP packet must be the same maximum segment size (MSS) or not. If the miniport driver does not set the SubMssFinalSegmentSupported capability, then each large UDP packet offloaded by the transport must have Length % MSS == 0. That is, the large packet is divisible into N packets with each packet segment containing exactly MSS user bytes. If the miniport driver sets the SubMssFinalSegmentSupported capability, then this packet length divisibility condition on the transport does not apply. In other words, the final segment can be less than MSS.

The driver should set the value of SubMssFinalSegmentSupported to NDIS_OFFLOAD_SUPPORTED if the miniport is capable of segmenting UDP sends where the total length of the large packet has a non-zero remainder when divided by MSS. When miniport driver support is indicated via this flag, the protocol driver is permitted to issue large UDP sends where the UDP payload length of the final segmented packet is less than MSS.

For more information, see UDP Segmentation Offload (USO).

IPv4.Reserved

Reserved. Miniport drivers must not read or write to this field.

IPv6

A structure within NDIS_UDP_SEGMENTATION_OFFLOAD that specifies IPv6 information, containing the following members:

IPv6.Encapsulation

Encapsulation settings for IPv6. For more information about this member, see the following Remarks section.

IPv6.MaxOffLoadSize

The maximum bytes of user data that the transport can pass to the miniport driver in a single packet. The transport will not pass a packet to the miniport driver that contains more user data bytes than MaxOffLoadSize specifies. If such a packet must be transmitted, the transport itself segments the packet into smaller packets.

IPv6.MinSegmentCount

The minimum number of segments that a large UDP packet must be divisible by before the transport can offload it to the hardware for segmentation. The transport will not offload a large packet to the miniport driver for segmentation unless the miniport driver can create at least as many segments as MinSegmentCount specifies from the packet. If a large UDP packet does not meet the minimum-segment requirement, the TCP/IP transport itself segments the packet into smaller packets.

IPv6.SubMssFinalSegmentSupported

A ULONG value that specifies whether all segments that a miniport driver derives from a large UDP packet must be the same maximum segment size (MSS) or not. If the miniport driver does not set the SubMssFinalSegmentSupported capability, then each large UDP packet offloaded by the transport must have Length % MSS == 0. That is, the large packet is divisible into N packets with each packet segment containing exactly MSS user bytes. If the miniport driver sets the SubMssFinalSegmentSupported capability, then this packet length divisibility condition on the transport does not apply. In other words, the final segment can be less than MSS.

The driver should set the value of SubMssFinalSegmentSupported to NDIS_OFFLOAD_SUPPORTED if the miniport is capable of segmenting UDP sends where the total length of the large packet has a non-zero remainder when divided by MSS. When miniport driver support is indicated via this flag, the protocol driver is permitted to issue large UDP sends where the UDP payload length of the final segmented packet is less than MSS.

For more information, see UDP Segmentation Offload (USO).

IPv6.Reserved1

Reserved. Miniport drivers must not read or write to this field.

IPv6.IpExtensionHeadersSupported

A ULONG value that a miniport driver sets to indicate that the miniport adapter can segment a large UDP packet whose IP header contains IPv6 extension headers.

IPv6.Reserved2

Reserved. Miniport drivers must not read or write to this field.

Remarks

Miniport drivers should set the values of this structure's fields and encapsulation requirements similarly to the NDIS_TCP_LARGE_SEND_OFFLOAD_V2 structure.

The NDIS_UDP_SEGMENTATION_OFFLOAD structure is used in the UdpSegmentation member of the NDIS_OFFLOAD structure. NDIS_UDP_SEGMENTATION_OFFLOAD specifies current or supported services that a miniport adapter provides for segmenting large UDP packets into smaller packets.

NDIS_OFFLOAD is used in the NDIS_MINIPORT_ADAPTER_OFFLOAD_ATTRIBUTES structure, NDIS_BIND_PARAMETERS structure, NDIS_FILTER_ATTACH_PARAMETERS structure, OID_TCP_OFFLOAD_CURRENT_CONFIG OID, and the NDIS_STATUS_TASK_OFFLOAD_CURRENT_CONFIG status indication.

For OID_TCP_OFFLOAD_CURRENT_CONFIG, the NDIS_OFFLOAD structure specifies the task offload capabilities that a miniport adapter supports. If the current offloads capabilities change, a miniport driver reports the new capabilities in an NDIS_STATUS_TASK_OFFLOAD_CURRENT_CONFIG status indication.

The Encapsulation members of NDIS_UDP_SEGMENTATION_OFFLOAD define the UDP encapsulation settings for the miniport adapter.

In response to an OID_TCP_OFFLOAD_CURRENT_CONFIG query request, NDIS provides a bitwise OR of the encapsulation flags, which indicate the supported encapsulation settings, in each of the Encapsulation members. Miniport drivers must provide Ethernet encapsulation (NDIS_ENCAPSULATION_IEEE_802_3). The other types of encapsulation are optional.

For an NDIS_STATUS_TASK_OFFLOAD_CURRENT_CONFIG status indication, the miniport driver provides a bitwise OR of the encapsulation flags, which indicate the current capabilities, in each of the Encapsulation members.

The following flags are defined for the Encapsulation members:

NDIS_ENCAPSULATION_NOT_SUPPORTED
Specifies that no encapsulation offload is supported.

NDIS_ENCAPSULATION_NULL
Specifies NULL encapsulation.

NDIS_ENCAPSULATION_IEEE_802_3
Specifies IEEE 802.3 encapsulation.

NDIS_ENCAPSULATION_IEEE_802_3_P_AND_Q
Specifies IEEE 802.3p and IEEE 802.3q encapsulation.

NDIS_ENCAPSULATION_IEEE_802_3_P_AND_Q_IN_OOB
Specifies that IEEE 802.3p and IEEE 802.3q encapsulation settings are specified in the NetBufferListInfo member of each NET_BUFFER_LIST structure.

NDIS_ENCAPSULATION_IEEE_LLC_SNAP_ROUTED
Specifies logical link control (LLC) encapsulation for routed protocols, as described in RFC 1483. This flag is also used to indicate Ethernet LLC/SNAP encapsulation.

Requirements

Requirement Value
Minimum supported client Windows 10, version 1912
Header ntddndis.h

See also

UDP Segmentation Offload (USO)