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Bug#647866: Network: Packages over hub via bnc not received

On Mon, 2011-11-07 at 01:48 +0100, debian wrote:
> Package: linux-base
> Version: 2.6.32-38
> Severity: normal
> Hello,
> sorry for this unspecific bug report / question:
> After installing debian squeeze the networking does not work in the
> following situation:
> Situation:
> I have a debian patched "Dockstar" (embedded system dockingstation NAS)
> box which is connected to a hub.
> This hub is connected via bnc-cable (coax) to another hub on which a
> linux box (Suse) is connected (router to internet).
> If Dockstar tries to connect to internet it "arps" for the gateway MAC
> (arp-request is seen on all netork parts with wireshark).
> The answer (arp-replay) is also seen an all network part.
> The arp table on the dockstar will not be updated by this communication
> ("arp -n" shows always "(incomplete)" for HWaddress) and continoues arp
> request can be seen.
> Any network packet directed to the dockstar can be seen on all parts of
> the network (this were seen with whireshark) but in debian there is
> nothing received.
> If I connect the debian-dockstar and the linuxbox over the same hub
> without bnc the communication is OK!
> It seems NOT to be a hardware problem of the dockstar, because with
> original firmware (also a linux) connection over bnc to internet works fine.
> I found a information on internet about problem with older hub/network
> hardware which inject some sort of incorrect crc errors
> http://www.plugcomputer.org/plugforum/index.php?topic=5772.msg18770#msg18770
> Is there a way to configure debian linux to ignore such crc errors?

CRC checking is a hardware feature and should not be disabled.  If you
were to do so, you would find that the contents of the received packets
are junk.

I would guess that the problem is related to signal levels.  Because you
are using hubs, signals have to travel all the way from one computer to
the other, whereas a switch or router will receive and re-transmit each
packet.  When you remove the coax cable you are shortening the distance
between the computers and so the received signal is stronger and there
are fewer errors.

Maybe the original firmware enables higher amplification for received
signals, so the network interface can properly decode weak signals.
What is the network driver and where is the source for the original

> What I do not understand is that all other linux boxes do not have this
> problem.

Because other people do not use 10BASE-2 and hubs!

> Is there a relevant change on kernel module concerning networking?



Ben Hutchings
You can't have everything.  Where would you put it?

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