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July 2014

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Subject:
Re: Fw: kvm bridge broadcast traffic
From:
Steven Timm <[log in to unmask]>
Reply To:
Steven Timm <[log in to unmask]>
Date:
Thu, 31 Jul 2014 08:58:05 -0500
Content-Type:
text/plain
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text/plain (55 lines) 
What network driver are you using inside the virtual machines?
virtio or some hardware emulation?

There are some layer 2 things that can go crazy in KVM every once
in a while, arps not arping when they should arp, etc.

Steve


On Thu, 31 Jul 2014, Andras Horvath wrote:

> Some update on this:
>
> I've created an identical virtualized environment an a different machine, and here the broadcast massages get forwarded to the guests. Only difference is the hardware.
>
> So could it really be the hw with the brand NIC? (Dell PowerEdge T110 II / Intel 82574L Gigabit)
>
>
> Thanks,
> Andras
>
>
> Begin forwarded message:
>
> Date: Thu, 31 Jul 2014 08:17:31 +0200
> From: Andras Horvath <[log in to unmask]>
> To: [log in to unmask]
> Subject: kvm bridge broadcast traffic
>
>
> Hi Everyone,
>
> I've run into a strange problem that I am not able to track down in the last 3 days. Could someone kindly help and give directions?
>
> On my 6.5 x64 system my bridged KVM guests (several kind of Windows and many kind of Linux guests) do not get the broadcast messages. Every network packets reach them from the subnet except broadcast and multicast messages. How can that be?
>
> In kernel the bridge filter by iptables is turned off - turning on STP does not help - enabling promisc mode in interface does not help either.
>
> Running tcpdump on host shows that the broadcast reaches the interface from a different computer on the subnet, but does not get in the guest. I ran tcpdump on the Linux guests and wireshark on the Windows ones. Testing the same with VirtualBox on a different computer, tcpdump and wireshark shows the broadcast packets.
>
> What is weird that every network packets reach my guests in KVM except the broadcast ones.
>
>
> Any help appreciated.
>
> Thanks,
> Andras
>

------------------------------------------------------------------
Steven C. Timm, Ph.D  (630) 840-8525
[log in to unmask]  http://home.fnal.gov/~timm/
Fermilab Scientific Computing Division, Scientific Computing Services Quad.
Grid and Cloud Services Dept., Associate Dept. Head for Cloud Computing

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