[En-Nut-Discussion] Slight problem with UDP

Ole Reinhardt ole.reinhardt at embedded-it.de
Mon Nov 2 22:33:45 CET 2009


> While playing with "icmp-udp.c", after some packet sniffing with
> FreeBSD's tcpdump i have noticed that the first packet sent by the
> ethernut was regularly lost.
> [...]
> The issue seem to be somehow ARP related, just adding a slight
> ( > 300 ms ) delay before start sending UDP packets to the server
> seem solve the problem ...

Indeed I noticed similar behaviour some time ago with the tftp
bootloader implementations of NutOS. The arp implementation did not
include a arp response. When the PC had sended an arp request and did
not get any reponse, the arp entry was deleted and no more packets were
accepted by the pc.

In your current configuration it might be possible that the first UDP
packet is send out before the arp challenge / response is finished, so
your pc does not have a complete arp table right at the beginning of
your program... (on the pc side).



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| Embedded-IT                                                 |
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