Re: TCP checksum and device driver eri0

>During a snoop session on a 280R with solaris 9 and network interface 
>eri0, I noticed that the TCP checksum field of every outgoing packet was 
>incorrect.

The eri0 interface and some other Solaris interfaces employ
hardware checksumming; as a result, packets with correct checksums
never exist in the kernel, they're generated in the hardware.

>The same packet snooped on the network has the correct checksum value.
>I believe that something happens between the snoop point on the machine 
>and the network interface eri0 output.
>I also tried on other machines:  on a Sun 450R with solaris 9 (but with 
>hme0) the TCP checksum snooped locally is correct, also on a Sun 250 
>with solaris 8 and hme0 is correct.

No hardware checksum for hme.

>With this last result I believe that the responsible is the eri0 driver. 
>It is true?
>If I want to snoop locally *but* with the correct checksum value, how 
>can I do?

You can disable hardware checksums:

	set ip:dohwcksum = 0

in /etc/system

Casper