Re: [lwip-users] tcp checksum error after the first frame.

[Kieran Mansley]

On Fri, 2008-01-18 at 10:43 +0000, Muhamad Ikhwan Ismail wrote:
> 
> Hi,
> 
> Yup its me again and the same problem but this time it involves TCP.
> 
> I have a weird case here :
> 
> 1. Client (lwip socket) sends a SYN
> 2.The echo server (Java server running on Windows PC) sends back SYN
> +ACK, checksum OK
> 3.Client sends a ACK.Sends some dummy data.
> 4.Server ACKs but with checksum error. And the server didnt echo back
> the dummy data.

So the packets sent by lwIP are fine, but the packets sent by your
Windows PC have a checksum error.  I can't see how lwIP would be to
blame for that.  The checksum error could be a red herring though: if
the NIC in your Windows PC does checksum offload, the packet as captured
by wireshark won't have the correct checksum (as it doesn't get
calculated and filled in until it is in the NIC) and so wireshark would
report it as a checksum error.

Why the PC isn't echoing the data I don't know though.  I think you're
going to have to debug your Windows server and Java app.

Kieran