RE: Entirely ignoring TCP and UDP checksum in kernel level

Josan Kadett
2004-08-21T08:00:28Z

The problem is that the interface 192.168.1.1 does not allow any tranmission
to occur. An implementation error I think... We send packets to 192.168.1.1,
we get no reply, but when we send packets to 192.168.77.1 we get the replies
(that is where the abnormality begins). However; the replies are now sourced
from 192.168.1.1 instead. That is, the blasted code in the device calculates
the checksum using the wrong IP address which it thinks it is assigned to...

-----Original Message-----
From: Aidas Kasparas [mailto:a.kasparas@gmc.lt]
Sent: Saturday, August 21, 2004 9:47 AM
To: Josan Kadett
Subject: Re: Entirely ignoring TCP and UDP checksum in kernel level

But will these checksums be incorect if crazy box would communicate with
address in 192.168.1.x only?

The whole idea was based on the fact, that if that box works well in
192.168.1.x networkd, then let it think it works in the network it knows
how to work!

Josan Kadett wrote:
> It is definetely impossible to use IPTables to handle packets with
incorrect
> checksums since NAT would drop the connection right away, otherwise I
would
> not have been asking this question here.
>
> -----Original Message-----
> From: Aidas Kasparas [mailto:a.kasparas@gmc.lt]
> Sent: Saturday, August 21, 2004 8:54 AM
> To: Josan Kadett
> Subject: Re: Entirely ignoring TCP and UDP checksum in kernel level
>
> How about setting up a separate box which would listen on that
> 192.168.77.1 address and MASQUERADE connections to your crazy box from
> 192.168.1.x address? Maybe then you would no longer need to break things
> in kernel?
>
>
>

--
Aidas Kasparas
IT administrator
GM Consult Group, UAB