82598EB Datasheet, PDF (244/596 Pages) Intel Corporation – Intel® 82598EB 10 Gigabit Ethernet Controller Datasheet

Encapsulating Security Payload
50
No Next Header
59
Intel^® 82598EB 10 GbE Controller - Transmit Functionality
Note 3
Note 2
Notes:
1. Hop by Hop Options Header is only found in the first Next Header Type of an IPv6 Header.
2. When a No Next Header type is encountered, the rest of the packet should not be processed.
3. Encapsulated Security Payload and Authentication – the 82598 cannot offload packets with this
header type.
4. The 82598 hardware acceleration does not support all IPv6 Extension header types, see Table 3-60.
5. The RFCTL.Ipv6_DIS bit must be cleared for this filter to pass.
UDP/TCP Filter
This filter checks for a valid UDP or TCP header. The prototype next header values are 0x11 and 0x06,
respectively.
3.5.3 Transmit Functionality
3.5.3.1 Packet Transmission
Output packets are made up of pointer-length pairs constituting a descriptor chain (called descriptor
based transmission). Software forms transmit packets by assembling the list of pointer-length pairs,
storing this information in the transmit descriptor, and then updating the on-chip transmit tail pointer to
the descriptor. The transmit descriptor and buffers are stored in host memory. Hardware transmits the
packet only after it has completely fetched all packet data from host memory and deposited it into the
on-chip transmit FIFO. This permits TCP or UDP checksum computation, and avoids problems with PCIe
under-runs.
Another transmit feature of the 82598 is TCP segmentation. The hardware has the capability to perform
packet segmentation on large data buffers off-loaded from the Network Operating System (NOS). This
feature is discussed in detail in Section 3.5.3.4.
Transmit tail pointer writes should be to EOP descriptors (the software device driver should not write
the tail pointer to a descriptor in the middle of a packet/TSO).
3.5.3.1.1 Transmit Data Storage
Data is stored in buffers pointed to by the descriptors. Alignment of data is on an arbitrary byte
boundary with the maximum size per descriptor limited only to the maximum allowed packet size (16
kB). A packet typically consists of two (or more) buffers, one (or more) for the header and one (or
more) for the actual data. Each buffer is referred by a different descriptor. Some software
implementations copy the header(s) and packet data into one buffer and use only one descriptor per
transmitted packet.
3.5.3.2 Transmit Contexts
The 82598 provides hardware checksum offload and TCP segmentation facilities. These features enable
TCP or UDP packet types to be handled more efficiently by performing additional work in hardware, thus
reducing the software overhead associated with preparing these packets for transmission. Part of the
parameters used to control these features are handled though contexts.
244