Intel PCI-X, Intel Gigabit Ethernet Controllers manual Supported Receive Checksum Capabilities

Receive and Transmit Description

The Packet checksum is the one’s complement over the receive packet, starting from the byte indicated by RXCSUM.PCSS (0b corresponds to the first byte of the packet), after stripping. For example, for an Ethernet II frame encapsulated as an 802.3ac VLAN packet and with RXCSUM.PCSS set to 14 decimal, the Packet Checksum would include the entire encapsulated frame, excluding the 14-byte Ethernet header (DA,SA,Type/Length) and the 4-byte q-tag. The Packet checksum does not include the Ethernet CRC if the RCTL.SECRC bit is set.

Software must make the required offsetting computation (to back out the bytes that should not have been included and to include the pseudo-header) prior to comparing the Packet Checksum against the TCP checksum stored in the packet.

For supported packet/frame types, the entire checksum calculation may be offloaded to the Ethernet controller. If RXCSUM.IPOFLD is set to 1b, the controller calculates the IP checksum and indicates a pass/fail condition to software by means of the IP Checksum Error bit (RDESC.IPE) in the ERROR field of the receive descriptor. Similarly, if the RXCSUM.TUOFLD is set to 1b, the Ethernet controller calculates the TCP or UDP checksum and indicates a pass/fail condition to software by means of the TCP/UDP Checksum Error bit (RDESC.TCPE). These error bits are valid when the respective status bits indicate the checksum was calculated for the packet (RDESC.IPCS and RDESC.TCPCS).

If neither RXCSUM.IPOFLD nor RXCSUM.TUOFLD is set, the Checksum Error bits (IPE and TCPE) is 0b for all packets.

Supported Frame Types include:

•Ethernet II

•Ethernet SNAP

Note: See Table 3-6for the 82544GC/EI supported receive checksum capabilities.

Table 3-5. Supported Receive Checksum Capabilities

Packet Type	HW IP Checksum	HW TCP/UDP Checksum
	Calculation	Calculation
IPv4 packets	Yes	Yes
IPv6 packets	No (n/a)	Yes
IPv6 packet with next header options:
Hop-by-Hop options	No (n/a)	Yes
Destinations options	No (n/a)	Yes
Routing	No (n/a)	Yes
Fragment	No (n/a)	No
IPv4 tunnels:
IPv4 packet in an IPv4 tunnel	No	No
IPv6 packet in an IPv4 tunnel	Yes (IPv4)	Yesa
IPv6 tunnels:
IPv4 packet in an IPv6 tunnel	No	No
IPv6 packet in an IPv6 tunnel	No	No
Packet is an IPv4 fragment	Yes	No
Packet is greater than 1552 bytes;	Yes	Yes
(LPE=1b)b
Packet has 802.3ac tag	Yes	Yes

32 Software Developer’s Manual