Wireshark · Ethereal-users: Re: [Ethereal-users] trying to figure out if error is caused by source or destination.

[Guy Harris <gharris@xxxxxxxxx>]

angelom@xxxxxxxxxxx wrote:
> My capture on a Microsoft network shows many many "checksum" errors 
> between two DNS servers that are on oposite ends of a VPN link.  How do 
> I determine if the error is being caused by the Source or the 
> Destination or one of the two VPN routers, or two CableModems.

On what machine are you capturing this traffic?  Is it on one of the two 
DNS servers, or are you capturing "passively" on another machine tapping 
into the network?

If it's on one of the two DNS servers, do you know whether the network 
interface on which you're capturing allow the checksums that have errors 
to be offloaded to the interface, and do *all* packets sent by that 
machine that have those checksum fields at all have checksum errors, and 
do most or all packets *received* by that machine have no checksum errors?

Also, do there appear to be responses to the packets that have checksum 
errors?

If that's all true, then this is probably just a side-effect of the 
checksum offloading, and the checksums actually transmitted are probably 
valid:

	http://www.ethereal.com/faq#q5.14