Intel Gigabit Ethernet Controllers ユーザーズマニュアル

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UDP pseudo header has the same format as the TCP pseudo header. The IPv4 pseudo header 
conceptually prefixed to the UDP header contains the IPv4 source address, the IPv4 destination 

address, the IPv4 protocol field, and the UDP length (same as the TCP Length discussed above). 

The IPv6 pseudo header for UDP is the same as the IPv6 pseudo header for TCP. This checksum 
procedure is the same as is used in TCP.

Note: The IP Destination Address is the final destination of the packet. Therefore, if a routing header is 

used, the last address in the route list is used in this calculation. The upper-layer packet length is 

the length of the UDP header and UDP payload.

Unlike the TCP checksum, the UDP checksum is optional. Software must set the TXSM bit in the 

TCP/IP Context Transmit Descriptor to indicate that a UDP checksum should be inserted. 

Hardware does not overwrite the UDP checksum unless the TXSM bit is set.

The Ethernet controller supports checksum off-loading as a component of the TCP Segmentation 

offload feature and as a standalone capability. 

 describes the interface for controlling 

the checksum off-loading feature. This section describes the feature as it relates to TCP 

Segmentation.

The Ethernet controller supports IP and TCP/UDP header options in the checksum computation for 

packets that are derived from the TCP Segmentation feature. The Ethernet controller is capable of 
computing one level of IP header checksum and one TCP/UDP header and payload checksum. In 

case of multiple IP headers, the driver has to compute all but one IP header checksum. The 

Ethernet controller calculates checksums on the fly on a frame by frame basis and inserts the result 
in the IP/TCP/UDP headers of each frame. TCP and UDP checksum are a result of performing the 

checksum on all bytes of the payload and the pseudo header.

IP Source Address

IP Destination Address

Zero

Layer 4 

Protocol ID

UDP Length

IP Source Address

IP Destination Address

Upper Layer Packet Length

Zero

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