Re: [lwip-users] win32 porting contrib: double IP address

[Joel Cunningham]

On 11/09/2017 03:41 AM, Giuseppe Modugno wrote:
> Il 08/11/2017 16:34, Joel Cunningham ha scritto:
> > > The ping works well if I launch "ping 192.168.1.156" command from 
> > > *another* computer on the same network.
> > You're most likely running into a checksum offload problem since you 
> > can't contact the LwIP stack from the Windows host, but you CAN from 
> > another machine.  The Window's TCP/IP stack is going to use checksum 
> > offloading for IPv4/UDP/TCP and during the transmit path, Winpcap 
> > will capture them before they go to hardware (where checksum is 
> > added).  Then they will fail checksum validation in LwIP and be 
> > discarded.
> >
> > You can verify this easily by opening up wireshark and capturing on 
> > the interface.  Wireshark (also using winpcap) will capture the 
> > packets at the same point and you can verify the checksum is missing.
> You're right.
>
> > If this is the case, you can disable checksum offloading in Windows 
> > for TX.
> What is the procedure to disable checksum offloading in Windows for TX?
It varies depending on your network card.  Easiest way is if the adapter 
has an option to disable it.  I have one like this.  For Win 7, Control 
Panel -> Network and Internet -> Network and Sharing Center -> Change 
Adapter Settings -> Right click adapter -> Properties -> Configure -> 
Advanced.  Then I have options like 'TCP Checksum Offload (IPv4)' which 
I can set to Disabled, RX or TX Disabled/Enabled

If you're card doesn't have those options, you'll have to set some 
registry values (Google for some how-to's).  I've had varying success 
with using registry values with different cards.

You can also use the command: 'netsh interface ipv4 show offload' to 
view the state of your adapters

Joel