I wrote 5 minutes ago:

> No, of course not. The tcp checksum is checked on reception. 
> So - please specify:
> 
> - what machine is seeing the checksum errors - the machine with NetBSD and
>   the bge interface or the other?
> 
> - what machine is receiving the bulk data stream - the machine with
> NetBSD and the bge interface or the other?

You mentioned in your original e-mail that ip4csum and udp4csum work fine.
I'm sure the person who'll eventually analyze the driver code wrt. your
problem will want to know this:

Did you leave them enabled for your tcp4csum tests? If yes, what's
the result without ip4csum? If not, what's the result with ip4csum?

Regards,
	-is