Ethereal-dev: RE: [Ethereal-dev] Re: (usagi-users 02308) Incorrect UDP checksum when using ro

Note: This archive is from the project's previous web site, ethereal.com. This list is no longer active.

Date Index Thread Index Other Months All Mailing Lists
Date Prev Date Next Thread Prev Thread Next
From: Richard Urwin <RUrwin@xxxxxxxxxxxxxx>
Date: Tue, 15 Apr 2003 15:49:06 +0100
> From: yoshfuji@xxxxxxxxxxxxxx [mailto:yoshfuji@xxxxxxxxxxxxxx]
> Sent: 15 April 2003 14:32
> In article <3E9C0EFB.8020308@xxxxxxxxxxxxxx> (at Tue, 15 Apr
> 2003 15:54:04 +0200), Yaniv Kaul <ykaul@xxxxxxxxxxxxxx> says:
>
> > I'm sending UDP packets from 3ffe:0:c0a8:979:290:27ff:febd:6ba9 to
> > 3ffe:0:a09:c901:2e0:18ff:fe22:391f via
> > 3ffe:0:c0a8:9c9:2a0:8eff:fe0c:2e1, using router header option.
> > It seems that the UDP checksum, when going out from the client is
> > incorrect, at least according to Ethereal. They are correct on the
> > server, therefore I think the checksum calc is done prior
> to taking into
> > account the routing.
>
> If the checksum is ok at the final receiver, it is fine.
> (checksum does not change while traveling.)
> It seems ethereal (or tchdump) does not calculate checksum
> properly.

More likely that the sender is off-loading the CRC calculations to the
NIC, surely. If one Ethereal sees the correct value it's unlikely that
Ethereal's calculations are faulty. This is IPv6 so I'm less certain
than I would be with IPv4. But with IPv4, Win2k and 3COM 3C905 the
outgoing CRCs are always wrong because they are calculated by the NIC or
the driver, after the point that they are tapped off for Ethereal. This
seems to be fairly common.


--
Richard Urwin, Software Design Engineer
Schenck Test Automation
Braemar Court, 1311b Melton Road, Syston, UK.
rurwin@xxxxxxxxxxxxx




> -----Original Message-----
>
> --
> Hideaki YOSHIFUJI @ USAGI Project <yoshfuji@xxxxxxxxxxxxxx>
> GPG FP: 9022 65EB 1ECF 3AD1 0BDF  80D8 4807 F894 E062 0EEA
>
> _______________________________________________
> Ethereal-dev mailing list
> Ethereal-dev@xxxxxxxxxxxx
> http://www.ethereal.com/mailman/listinfo/ethereal-dev
>
> ______________________________________________________________
> __________
> This email has been scanned for all viruses by the MessageLabs SkyScan
> service. For more information on a proactive anti-virus
> service working
> around the clock, around the globe, visit http://www.messagelabs.com
> ______________________________________________________________
> __________
> 

________________________________________________________________________
This email has been scanned for all viruses by the MessageLabs SkyScan
service. For more information on a proactive anti-virus service working
around the clock, around the globe, visit http://www.messagelabs.com
________________________________________________________________________