Wireshark-users: Re: [Wireshark-users] Checksum incorrect on the IP layer on RTP packets
Hi,
So what's the problem? A network card might as well calculate the checksum
of IP.
Title:
IP checksum offload
United States Patent 5898713
Abstract:
A technique enables a control unit to perform checksum operations for
packets, which operations are otherwise performed by a host computer of a
computer network. The technique involves the use of two data links coupled
between the host and control unit; one data link is used for exchanging
"normal" IP packets without checksum operations performed thereon by the
control unit and the other link is used for exchanging IP packets that have
undergone or will undergo checksum operations by the control unit. By
"offloading" checksum operations to the control unit, the technique reduces
processor cycles consumed by the host, thereby improving the performance of
the host computer and network.
Thanx,
Jaap
On Wed, 12 Aug 2009 18:21:31 +0300, Boaz Galil <boaz20@xxxxxxxxx> wrote:
> Guys,
>
> I am familiar with TCP checksum offloading but I am talking about RTP
> (over
> UDP). and the checksum incorrect is on the level of the IP layer not
the
> UDP level....
>
>
>
>
> On Wed, Aug 12, 2009 at 6:07 PM, Jaap Keuter <jaap.keuter@xxxxxxxxx>
wrote:
>
>> Hi Roger,
>>
>> Sorry, but he's talking about IP checksums and RTP, which is over UDP,
>> not
>> TCP.
>> But still the concept is the same.
>>
>> Thanx,
>> Jaap
>>
>> On Wed, 12 Aug 2009 07:46:08 -0700, "Wynns, Roger [OXFORD]"
>> <RWynns@xxxxxxxxxxx> wrote:
>> > Have a look at TCP checksum offloading :-)
>> >
>> > (http://wiki.wireshark.org/TCP_checksum_offload)
>> >
>> >
>> >
>> > Roger
>> >
>> >
>> >
>> > From: wireshark-users-bounces@xxxxxxxxxxxxx
>> > [mailto:wireshark-users-bounces@xxxxxxxxxxxxx] On Behalf Of Boaz
Galil
>> > Sent: Wednesday, August 12, 2009 9:37 AM
>> > To: Community support list for Wireshark
>> > Subject: [Wireshark-users] Checksum incorrect on the IP layer on RTP
>> > packets
>> >
>> >
>> >
>> >
>> >
>> >
>> > Checksum error in the IP layer on RTP packet
>> >
>> >
>> >
>> > Dear experts,
>> >
>> > Please consider the following scenario:
>> >
>> > Computer A streams RTP packets to Computer B.
>> >
>> > I have set up wire shark on both computer A and computer B. The
>> > packet capture that I collected from computer A (filtered for RTP
>> > packets) showed me that each packet has "incorrect checksum" on the
IP
>> > level on all the RTP packets. The packet capture that I collected
from
>> > computer B showed me "correct checksum" on all the RTP packets.
>> >
>> > Can someone please explain me what I am observing here and how could
it
>> > be possible that on one side the checksum is Incorrect (the sender
>> > side)
>> > and on the second side (the receiver side) the checksum is correct?
>> >
>> >
>> >
>> > Thanks in advance,
>> >
>> > Boaz Galil.
>>
>>
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