82598EB Datasheet, PDF (238/596 Pages) Intel Corporation – Intel® 82598EB 10 Gigabit Ethernet Controller Datasheet

Intel^® 82598EB 10 GbE Controller - Receive Functionality
framing layer header has been stripped out. Therefore, the source IPv4 address is referred to as
@12-15, while the destination v4 address is referred to as @16-19.
• @x-y, @v-w denotes concatenation of bytes x-y, followed by bytes v-w, preserving the order in
which they occurred in the packet.
All hash function variations (IPv4 and IPv6) follow the same general structure. Specific details for each
variation are described in the following section. The hash uses a random secret key of length 320 bits
(40 bytes); the key is generally supplied through the RSS Random Key (RSSRK) register.
The algorithm works by examining each bit of the hash input from left to right. Intel’s nomenclature
defines left and right for a byte-array as follows: Given an array K with kB, Intel’s nomenclature
assumes that the array is laid out as follows:
K[0] K[1] K[2] … K[k-1]
K[0] is the left-most BYTE, and the MSB of K[0] is the left-most bit.
K[k-1] is the right-most byte, and the LSB of K[k-1] is the right-most bit.
ComputeHash(input[], N)
For hash-input input[] of length N bytes (8N bits) and a random secret key K of 320 bits
Result = 0;
For each bit b in input[] {
if (b == 1) then Result ^= (left-most 32 bits of K);
shift K left 1 bit position;
}
return Result;
The following four pseudo-code examples are intended to help clarify exactly how the hash is to be
performed in four cases, IPv4 with and without ability to parse the TCP header, and IPv6 with an
without a TCP header.
3.5.2.10.1.1 Hash for IPv4 with TCP
Concatenate SourceAddress, DestinationAddress, SourcePort, DestinationPort into one single byte-
array, preserving the order in which they occurred in the packet: Input[12] = @12-15, @16-19, @20-
21, @22-23.
Result = ComputeHash(Input, 12);
3.5.2.10.1.2 Hash for IPv4 with UDP
Concatenate SourceAddress, DestinationAddress, SourcePort, DestinationPort into one single byte-
array, preserving the order in which they occurred in the packet: Input[12] = @12-15, @16-19, @20-
21, @22-23.
Result = ComputeHash(Input, 12);
3.5.2.10.1.3 Hash for IPv4 without TCP
Concatenate SourceAddress and DestinationAddress into one single byte-array
Input[8] = @12-15, @16-19
Result = ComputeHash(Input, 8)
3.5.2.10.1.4 Hash for IPv6 with TCP
Similar to above:
Input[36] = @8-23, @24-39, @40-41, @42-43
Result = ComputeHash(Input, 36)
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