Another Ethernet problem for Thomas :)

Thomas Doerfler Thomas.Doerfler at
Wed Jan 30 06:24:18 CST 2008

Hash: SHA1

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 :-)

Ok, no more kidding. ;-)

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();

- - 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?


| Hello, all and Thomas especially! :)
| The last time Thomas's help was so effective, that I hope he knows the
| decision of my (I hope the last) today's problem:
| Using netdemo application I send UDP packets to the Linux box with nc -lu
| waiting. I press 'u' in console and it starts sending UDP packets.
| Everything works fine, but approximately once per 7-10 restarts I see
that the
| very first packet does not arrive!
| I put counter into the packets and can see its '0' value is missed rarely
| after restart.
| I run tcpdump to check and also saw when this occurs, that the first
packet is
| missed in the tcpdump too.
| What can it be and how can I debug the situation?
| [Each time I put breakpoint in the driver at buffer sending the
problem never
| occurs.:( But there are other packets too...]
| Thanks a lot ahead.

- --
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D-82178 Puchheim          Germany
email:    Thomas.Doerfler at
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