[Dibbler] Two Advertise and two Reply messages from dibbler-server on Linux

Tomek Mrugalski thomson at klub.com.pl
Thu Aug 13 12:07:15 CEST 2015

On 12/08/15 23:57, Mike Taylor wrote:
> I’m having a problem with Dibbler 1.0.1 server running in a Linux VM and
> hoping somebody can shed some light on it.  The problem does not occur when it runs on Windows.
Out of curiosity, did you use 32 or 64 bits? I haven't tested 64 bit
myself and was wondering whether it's functional or not.

> In the Linux VM the client receives two Advertise and two Reply messages
> for each of its Solicit and Request message respectively. 
I tested 1.0.1 briefly before the release, but haven't seen any
duplicates. I'm leaving for a couple days off, so can't really look into
the problem. If the problem is still unresolved by next week, I'll try
to investigate it.

> I don’t have a Linux machine other than a VirtualBox VM to test on at
> the moment so I don’t know if this could somehow be related to it running in a VM but it isn’t
> at all clear why it would be.  The message are, after all, not entirely duplicates of one another
> as noted.  Well, I  suppose if somehow it got two copies of the client message… but I don’t
> see that in packet captures whether made in the Linux VM or on Windows which is hosting the VM.
I'm doing most of my testing on VirtualBox and it's working fine.

I don't have any specific advice at this time. I would look into the
dibbler log and see how many packets it says were received and how many
sent (on info level, all incoming and outgoing packets are logged). If
the dibbler server admits it received one message, but sent 2 responses,
it would clearly indicate server bug. On the other hand, if there are
entries for 2 received messages, it would be likely a misconfiguration.
Maybe dibbler is told to bind sockets in odd way, so it gets a
duplicate? I think it would be possible to tell the server to
listen on unicast address and specify its link-local there. It would
then bind the socket twice: once as it opens socket on link-local and
then second time thinking it binds to a global or ULA address, which
effectively binding to the same address the second time. Maybe VM has
two interfaces connected to the same network and dibbler listens on both?.

These are shot in the dark type of questions, I'm afraid. I may be able
to offer more specific suggestions or solution when I look into this
matter further next week.

Good luck,

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