[libvirt-users] RX dropped packets on guests subnets

[pichon]

Arvin,

Thanks a lot for pointing tcpdump.
What I have observe is that the packets which seems to be dropped are STP related

[root at network ~]# tcpdump -i eth0
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
23:15:37.967118 STP 802.1d, Config, Flags [none], bridge-id 8000.52:54:00:e4:ec:1b.8003, length 35
23:15:39.967163 STP 802.1d, Config, Flags [none], bridge-id 8000.52:54:00:e4:ec:1b.8003, length 35
23:15:41.967121 STP 802.1d, Config, Flags [none], bridge-id 8000.52:54:00:e4:ec:1b.8003, length 35
23:15:43.967147 STP 802.1d, Config, Flags [none], bridge-id 8000.52:54:00:e4:ec:1b.8003, length 35
23:15:45.967118 STP 802.1d, Config, Flags [none], bridge-id 8000.52:54:00:e4:ec:1b.8003, length 35
23:15:47.967156 STP 802.1d, Config, Flags [none], bridge-id 8000.52:54:00:e4:ec:1b.8003, length 35
23:15:49.967131 STP 802.1d, Config, Flags [none], bridge-id 8000.52:54:00:e4:ec:1b.8003, length 35
23:15:51.967132 STP 802.1d, Config, Flags [none], bridge-id 8000.52:54:00:e4:ec:1b.8003, length 35
23:15:53.967195 STP 802.1d, Config, Flags [none], bridge-id 8000.52:54:00:e4:ec:1b.8003, length 35
23:15:55.967138 STP 802.1d, Config, Flags [none], bridge-id 8000.52:54:00:e4:ec:1b.8003, length 35
23:15:57.967165 STP 802.1d, Config, Flags [none], bridge-id 8000.52:54:00:e4:ec:1b.8003, length 35

Now, my main issue is that I observe those packets also in the disabled virtio-net driver (with driver name=qemu), but in that case, no packets are dropped 

So is that a different behaviour of the bvirtio-net when it is in Kernel mode and when it is in User space ?

Patrick


> On 26 Jan 2016, at 20:51, Troels Arvin <troels at arvin.dk> wrote:
> 
> pichon wrote:
> 
> Hello,
> 
> pichon wrote:
>> On each of my guests VM, I see constantly a RX dropped number increasing
>> , Even if the VM does nothing !
> 
> I'm seeing the same phenomenon on one of our LANs (on another LAN, I 
> don't see it). My setup is with RHEL 7, and it is seen on both physical 
> and virtual servers. I don't see it on any RHEL 5 or 6 servers.
> 
> A strange observation: If I start tcpdump, the package drops stop. 
> (Setting the NIC in promisc mode does not have any impact; it has to be 
> tcpdump.)
> 
> I suspect that it has to do with this:
> https://www.netiq.com/support/kb/doc.php?id=7007165
> If this is the case, it's simply because recent kernels classify packets, 
> and then there's nothing to worry about.
> 
> - But Red Hat Support does not share that view. I have an open case with 
> Red Hat Support about it; lots of stuff has been tried, but we have yet 
> to reach a conclusion.
> 
> -- 
> Troels
> 
> 
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