Filter
Top Products
Intel
®
82575EB Gigabit Ethernet Controller — Receive Packet Checksum Offloading
Intel
®
82575EB Gigabit Ethernet Controller 324632-003
Software Developer’s Manual and EEPROM Guide Revision: 2.1
132 January 2011
5.5.1.5 IPv6 Extension Headers
IPv4 and TCP provide header lengths that allow hardware to easily navigate through these headers on
packet reception for calculating checksums and CRCs, etc. For receiving IPv6 packets, however, there is
no IP header length to help hardware find the packet's ULP (such as TCP or UDP) header. One or more
IPv6 extension headers might exist in a packet between the basic IPv6 header and the ULP header.
Hardware must skip over these extension headers to calculate the TCP or UDP checksum for received
packets.
The IPv6 header length without extensions is 40 bytes. The IPv6 field Next Header Type indicates what
type of header follows the IPv6 header at offset 40. It might be an upper layer protocol header such as
TCP or UDP (Next Header Type of 6 or 17, respectively), or it might indicate that an extension header
follows. The final extension header indicates with its Next Header Type field the type of ULP header for
the packet.
IPv6 extension headers have a specified order. However, destinations must be able to process these
headers in any order. Also, IPv6 (or IPv4) can be tunneled using IPv6, and thus another IPv6 (or IPv4)
header and potentially its extension headers can be found after the extension headers.
The IPv4 Next Header Type is at byte offset 9. In IPv6, the first Next Header Type is at byte offset 6.
All IPv6 extension headers have the Next Header Type in their first 8 bits. Most have the length in the
second 8 bits (Offset Byte[1]) as shown:
Table 35 lists the encodings of the Next Header Type field and information on determining each header
type's length. The IPv6 extension headers are not otherwise processed by the 82575 so details are not
covered.
123
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
Next Header Type Length