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Receive and Transmit Description
60 Software Developer’s Manual
Note: It is recommended that the entire header section, as described by the TCP Context Descriptor
HDRLEN field, be coalesced into a single buffer and described using a single data descriptor.
3.5.7 IP and TCP/UDP Headers
This section outlines the format and content for the IP, TCP and UDP headers. The Ethernet
controller requires baseline information from the software device driver in order to construct the
appropriate header information during the segmentation process.
Header fields that are modified by the Ethernet controller are highlighted in the figures that follow.
The IPv4 header is first shown in the traditional (RFC 791) representation, and because byte and bit
ordering is confusing in that representation, the IP header is also shown in little-endian format. The
actual data is fetched from memory in little-endian format.
Figure 3-8. IPv4 Header (Traditional Representation)
1 23
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
Version
IP Hdr
Length
TYPE of service
Total length
Identification Flags Fragment Offset
Time to Live Layer 4 Protocol ID Header Checksum
Source Address
Destination Address
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