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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 155
A type 0 routing header contains the following format:
Figure 18. IPv6 Routing Header (Traditional Representation)
• Next Header - 8-bit selector. Identifies the type of header immediately following the routing header.
Uses the same values as the IPv4 Protocol field [RFC-1700 et seq.].
• Header Extension Length - 8-bit unsigned integer. Length of the routing header in 8-octet units, not
including the first 8 octets. For the Type 0 Routing header, Header Extension Length is equal to two
times the number of addresses in the header.
• Routing Type - 0
• Segments Left - 8-bit unsigned integer. Number of route segments remaining. For example, the
number of explicitly listed intermediate nodes still to be visited before reaching the final
destination. Equal to "n" at the source node.
• Reserved - 32-bit reserved field. Initialized to zero for transmission; ignored on reception.
• Address[1...n] - Vector of 128-bit addresses, numbered 1 to n.
The 82575 supports checksum off-loading as a component of the TCP Segmentation offload feature and
as a standalone capability. Section 3.8.7 describes the interface for controlling the checksum off-
loading feature. This section describes the feature as it relates to TCP Segmentation.
The 82575 supports IP and TCP/UDP header options in the checksum computation for packets that are
derived from the TCP Segmentation feature.
Note: The 82575 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 82575 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.
Three specific types of checksum are supported by the hardware in the context of the TCP
Segmentation offload feature:
• IPv4 checksum
• TCP checksum
• UDP checksum
Each packet that is sent via the TCP segmentation offload feature optionally includes the IPv4
checksum and either the TCP or UDP checksum.
Next Header Hdr Ext Len Routing Type 0 Segments Left n
Reserved
Address[1]
Address[2]
…
Final Destination Address[n]