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IP and TCP/UDP Headers — Intel
®
82575EB Gigabit Ethernet Controller
324632-003 Intel
®
82575EB Gigabit Ethernet Controller
Revision: 2.1 Software Developer’s Manual and EEPROM Guide
January 2011 151
• UDP Header:
— The 82575’s DMA function fetches the Ethernet, IP, and TCP/UDP prototype header information
from the initial descriptor(s) and save them on-chip for individual packet header generation.
The following sections describe the updating process performed by the hardware for each frame
sent using the TCP Segmentation capability.
5.8.6 IP and TCP/UDP Headers
This section outlines the format and content for the IP, TCP and UDP headers. The 82575 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 82575 are highlighted in the figures that follow.
Note: IPv4 requires the use of a checksum for the header. IPv6 does not use a header Checksum.
IPv4 length includes the TCP and IP headers as well as data. IPv6 length does not include
the IPv6 header.
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 10. IPv4 Header (Traditional Representation)
1 2 3
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
Options
Byte3 Byte2 Byte1 Byte0
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
LSB Total length MSB TYPE of Service Version IP Hdr
Length
Fragment Offset Low R
E
S
N
F
M
F
Fragment Offset
High
LSB Identification MSB
Header Checksum Layer 4 Protocol ID Time to Live
Source Address
Destination Address
Options