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Hello,
I have a situation:
My system is able to send UDP packet to remote IP. I'm using windump (it shows network traffic), so i'm 100 % sure, that these packets i'm sending, are definitly UDP, and their's local and remote IPs and ports are correct. To test if it really works, i have connected some other computer to my 'host' machine (this is the machine on which bochs with my system is running), on both computers is windump up and running. Then i have written a pretty simple UDP server, that can detect incoming connection, notice me about this fact, and then it will just print the incoming data on the screen.
I have tried it with UDP netcat, and it works perfectly. But when i try to send UDP packet from my system, server does nothing.
I can see (according to windump) how the packet left the host machine (bochs is configured to use real netcard) with correct source and destination IPs and ports - and then i can see that very packet coming to that other computer (again, according to windump), but the server (that crappy app i have written for testing purposes) does nothing.
So again: the packet get properly received by the other computer, but it does not go futher (to my app).
Any ideas, what could be wrong?

Are you using the correct destination MAC address? Is your server listening on the correct interface (i.e. not from localhost only)?

whoups, MACs are set to fake values...i'll try to set them right.

MAC is correct, no effect.

So really no idea what can be wrong? I noticed that checksum field is zeroed, it could be it? But according to what i have read about udp - when ipv4 is used, no checksum have to be provided. Source MAC is also faked, but that does not matter i guess..am i right? Destination MAC is correct.
Any guesses? Seriously, anything.

"Then i have written a pretty simple UDP server, that can detect incoming connection"

...UDP doesn't have connections...

..... I know that .. I guess that you know how i ment it, but ok, correction: 'it is able to detect if incoming data are available' ..

Actually there are 2 checksum fields. One for IP header and another one for UDP. UDP's checksum is optional and can use all-zeros value. But what about IP's one?

I'm not sure, if IP checksum is mandatory or not. I'll try to cumpute that checksum and see if it helps.

IP checksum corrected, no effect.

Solved. For those that are interrested: for proper receive of UDP packet (from netcard memory to software layer) you must have correct IP's and UDP's checksumes (even if ipv4 is used - datasheet is wrong about this..), IP and UDP length field must also be correct.
Source ip/port and MAC can be any value i guess, but you have to always calculate checksumes properly - altough the netcard will receive it, but OS software layer will discard it. (which was subject of this topic).
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