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bad TCP checksums

Has anybody seen problems with bad TCP checksums with NE2000-compatible
PCI Ethernet cards (ep0)? I'm getting lousy throughput on my internal network,
because of lots of packets like this ( is the OpenBSD machine):

Flags: 0x00
Status: 0x00
Packet Length:1518
Timestamp: 08:24:40.916574 07/31/98
Ethernet Header

Source: 00:e0:29:18:26:c0
Protocol Type:0x0800 IP
IP Header - Internet Protocol Datagram

Header Length: 5
Precedence: 0
Type of Service: %0100 Maximize Throughput
Unused: %0
Total Length: 1500
Identifier: 41555
Fragmentation Flags: %000
Fragment Offset: 0
Time To Live: 64
IP Type: 0x06 TCP
Header Checksum: 0x2871
Source IP Address:
Dest. IP Address:
No Internet Datagram Options
TCP - Transport Control Protocol

Source Port:
Destination Port: 2092
Sequence Number: 2733245417
Ack Number: 2336981505
Offset: 5
Reserved: %000000
Code: %010000
Ack is valid
Window: 17520
Checksum: 0x4461 Checksum invalid. Should be: 0x5b32
Urgent Pointer: 0
No TCP Options
Jim Lippard lippard_(_at_)_discord_(_dot_)_org
Phoenix, Arizona http://www.discord.org/
PGP Fingerprint: 35 65 66 9F 71 FE 50 57 35 09 0F F6 14 D0 C6 04