Re: vge(4) bad checksum

On Fri, Dec 22, 2006 at 11:02:02AM +0300, Ruslan Ermilov wrote:
> Hi,
> 
> On Sun, Dec 17, 2006 at 03:52:49PM -0500, Kris Kennaway wrote:
> > On Sun, Dec 17, 2006 at 11:46:24PM +0300, Andrew Pantyukhin wrote:
> > > I'm not sure what it's all about, but with today's
> > > current whatever goes out my vge interface (icmp/
> > > tcp/udp) has bad checksum:
> > 
> > This is a FAQ; it's probably using hardware checksum offloading.
> > 
> > Since the packet passed down to the NIC does not yet have the checksum
> > computed, it looks to tcpdump like the checksum is incorrect.  However
> > if you look at the packet actually transmitted by the NIC
> > (e.g. tcpdump on another host), you'll see that it has the correct
> > checksum.
> > 
> Kris, you probably missed a commit by csjp_at_ where it was fixed.
> 
> : revision 1.220
> : date: 2006/11/18 23:17:22;  author: csjp;  state: Exp;  lines: +40 -0
> : Currently, drivers that support hardware offload of VLAN tag
> : processing are forced to toggle this functionality when the card
> : is put in and out of promiscuous mode.  The main reason for this
> : is because the hardware strips the VLAN tag, making it impossible
> : for the tag information to show up in network diagnostic tools like
> : tcpdump(1).
> : [...]

That sounds like an unrelated issue (VLAN tagging, not checksum
offloading).

Kris