confused by various UDP checksum algorithms

magnetron Guest #2983151
Rate this post
• ▲ useful
▼ not useful 
hello forum,

I am trying to send an UDP packet (contains only "TEST" string)
from STM32 to VB6 winsock
I can see packets going with wireshark software

however winsock data_arrival subroutine never gets called
( if I send from laptop winsock to PC winsock or vice versa  UDP packet 
is received OK )

I am suspecting that I cannot calculate UDP checksum correct

in google every single example calculates the UDP checksum different way

my question ,

has anybody a correct algorithm for UDP checksum ?
( which he has tested to be true )

thank you
Reply Quote Edit Move Thread sperren Anmeldepflicht aktivieren Anpinnen Delete topic Thread mit anderem zusammenführen Report post
magnetron Guest #2983193
Rate this post
• ▲ useful
▼ not useful 
I have run uIP demo supplied with the development board already - no 
problem

however uIP code is too complex to understand

besides I dont need TCP/IP
I only need send an receive a simple UDP packet to PC

coming to UDP checksum ; I have tried with checksum field zero
no success
Reply Quote Edit Delete Report post
(prx) A. K. #2985389
Rate this post
• ▲ useful
▼ not useful 
Packets which are invalid at the ethernet level won't arrive at 
Wireshark. Also, in my experience, Wireshark complains when it 
encounters a bad packet. Since Wireshark does not complain (in the 
screen shot shown above), it likely is formally correct at the UDP level 
as well.

Since you had a working packet sent via laptop: Is the checksum really 
the only difference between those frames? Doing a side by side 
comparison.

Concerning the checksum: You told, that you already found several code 
snippets for it. Likely most or all of them produce a correct result at 
least on the platform they were written for. So getting a few more 
slightly different snippets likely won't help a lot.

Anyway, there are authoritative sources: The RFCs for UDP (768) and for 
the IP checksum calculation (1071). RFC 1071 even includes sample code.
Reply Quote Edit Delete Report post
Watch this topic

Reply

Note: the original post is older than 6 months. Please don't ask any new questions in this thread, but start a new one.

Formatting
  • [c]C-Code[/c]
  • [code]code in other languages, ASCII drawings[/code]
  • [math]formula (LaTeX syntax)[/math]
  • [[Title]] – link to an article
  • Link to another post: right-click its post ID (#8078628), copy the address, paste it into the text

More about formatting

Post long source code as an attachment, not in the text.

Your name and e-mail address

Already registered? Log in

Not shown to anyone. We send you a link; your post appears once you confirm it there.

By submitting you create a free account and accept the terms of use.