Subject: kern/18032: hardware checksum broke in (some?) ex
To: None <>
From: None <>
List: netbsd-bugs
Date: 08/22/2002 02:46:56
>Number:         18032
>Category:       kern
>Synopsis:       hw csum causes cksum errors on ex controllers
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Aug 21 19:47:01 PDT 2002
>Originator:     William Coldwell
>Release:        NetBSD-1.6_BETA4
Architecture: i386
Machine: i386
When tracking down another issue, I noticed an usual amount of "bad [tcp] cksum"
in the output of tcpdump -vvv.  Since I have a variety of 3Com ex cards in
both i386 and alpha machines, I was able to attribute it to the cards, and then
to the hardware csum by turning it off and on and monitoring the number.  When
hw csum is turned off, there are virtually no errors.  With it on, there are
lots... especially on a network loaded machine.

On a machine with an ex card (3c450-TX, 3c905C-TX tested)
In one window, tcpdump -vvv | grep "bad ".
Watch for errors.
ifconfig ex0 -udp4csum -ip4csum -tcp4csum
Watch the errors go away
ifconfig ex0 udp4csum ip4csum tcp4csum
Watch the errors come back.