Re: [lwip-users] UDP send problem

[Kieran Mansley]

On Tue, 2010-10-12 at 11:10 +0200, Andrea Visinoni wrote:
> i just modified a HTTP client example to send an UDP packet to my NTP 
> server. But it works only if i send my packet 3 times, the first 2
> send 
> are not working.
> With the HTTP original example it was working correctly since the
> first 
> write.
> Any hits? I'm using FreeRTOS + lwip 1.3.2 on a AT32UC3A board

First guess: TCP works because it retransmits and guarantees a reliable
link.  UDP doesn't because there are initial losses and it is up to the
application to cope with these and resend if necessary.  My guess about
the initial losses is that you don't have an entry in your ARP table
when you do the first send and ARP queueing is disabled so the packets
are just dropped until the ARP response is received and the MAC address
is known.

Kieran