[En-Nut-Discussion] ARP and UDP

Paolo Simoncelli simonp at email.it
Fri Nov 6 13:27:51 CET 2009

Hi all,

Following my previous post about this question, after a lot of
packet sniffing with ettercap, wireshark and tcpdump.
i can definitively say that if you throw out an UDP packet
very early (seems about before 500 ms) after opening the socket
it gets lost into the TCP guts of NutOs :( ...

In his reply Ole pointed out that if was possible that
ethernut fired the packet too early for the UDP server
to complete his ARP table, but it seems to me that the
problem is on the ethernut side, :( things go like this:

ARP request starts from ethernut
the server replies with its IP

then two cases:
if you send an UDP packet within 500 ms, just
nothing  comes out from the etherenet

if you send an UDP packet after 500 ms all is fine

probably ethernut has not built its ARP table
and just silently discards the packet, second one
goes like a breeze !

NutSleep(500); before sending out the first packet
resolves the issue

maybe TCP seems not affected by this behaviour due to
protocol retries that mask the problem

Sorry to appear pedantic about this question,
but i'm developing an application that sends out
just one packet ;-) ...


 Caselle da 1GB, trasmetti allegati fino a 3GB e in piu' IMAP, POP3 e SMTP autenticato? GRATIS solo con Email.it http://www.email.it/f
 Legal.email.it: il servizio di Posta elettronica certificata con SMS di notifica per aziende e liberi professionisti. Secondo la normativa vigente l'ultimo giorno per mettersi in regola è il 29 novembre 2009.
 Clicca qui: http://adv.email.it/cgi-bin/foclick.cgi?mid=8979&d=6-11

More information about the En-Nut-Discussion mailing list