Intel PCI User Manual

32

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 

 for the 82544GC/EI supported receive checksum capabilities.

IPv4 packets

Yes

Yes

IPv6 packets

No (n/a)

Yes

IPv6 packet with next header options:
Hop-by-Hop options
Destinations options
Routing
Fragment

No (n/a)
No (n/a)
No (n/a)
No (n/a)

Yes
Yes
Yes
No

IPv4 tunnels:
    IPv4 packet in an IPv4 tunnel
    IPv6 packet in an IPv4 tunnel

No
Yes (IPv4)

No
Yes

a

IPv6 tunnels:
    IPv4 packet in an IPv6 tunnel
    IPv6 packet in an IPv6 tunnel

No
No

No
No

Packet is an IPv4 fragment

Yes

No 

Packet is greater than 1552 bytes; 
(LPE=1b)

b

Yes

Yes

Packet has 802.3ac tag

Yes

Yes