Another Ethernet problem for Thomas :)

Leon Pollak leonp at
Wed Jan 30 06:56:05 CST 2008

On Wednesday, 30 בJanuary 2008, Thomas Doerfler wrote:
> Leon Pollak schrieb:
> Here is the simple solution:
> Today we have detected some spurious UDP packets arriving on our
> firewall. They all had a counter value of ZERO and came from the domain
> "". So now I know how they were sent. Leon, if you like, I can
> send them back as attachment in a separate email :-)
Yes, yes!!! Please!!!

> So now you got me, I have no idea what can actually be the reason for
> this (Oh, just a hint, it is a software problem).
> What I would do:
> - check, that the statistics counters of the driver are coded properly,
> so they really count all packets sent, all tx errors etc.
> - compare the number of packets sent with the number of packets tcpdump
> can count (using the rtems_bsdnet_show_if_stats() function)
> additionally you might want to use the following functions to get more
> statistics output:
> ~    rtems_bsdnet_show_icmp_stats();
> ~    rtems_bsdnet_show_ip_stats();
> ~    rtems_bsdnet_show_inet_routes();
> ~    rtems_bsdnet_show_tcp_stats();
> ~    rtems_bsdnet_show_udp_stats();
> - check, that no mbufs are lost over time:
> ~    rtems_bsdnet_show_mbuf_stats();
I am rather weak in this area. IMHO, there were no such errors and counters 
look normal.
Now, I have noticed the strange (IMHO) event, may be it has something in 
common with my problem...

tcpdump shows that after unit start there is the following packet:
	arp who-has tell
where is the address of the unit.
Is this normal?

Tracking down, I saw that the arp request appears in rtems_bsdnet_setup which 
calls rtems_bsdnet_ifconfig(ifp->name, SIOCSIFADDR, &address).

> - Just a guess (no, not again!): Does the packet loss only occur, when
> you have waited some minutes after the last transmission? maybe some
> switch/arp cache/xxx has lost routing information then and needs one
> packet to get things working again?
Can it be so!?
Well, after some thoughts I how can it be, because tcpdump shows:
	arp who-has tell 
	(my unit to my pc)
as the first packet. Thus it should be lost, not my UDP packet, no?


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