[ovs-discuss] OVS not forwarding packets to port

Chris Picton chris at picton.nom.za
Wed Mar 18 15:14:30 UTC 2015

On 03/18/15 16:52, Ben Pfaff wrote:
> On Wed, Mar 18, 2015 at 12:44:08PM +0200, Chris Picton wrote:
>> On 03/18/15 08:47, Chris Picton wrote:
>>> The relevant flow is:
>>> recirc_id(0),skb_priority(0),in_port(2),eth(src=00:15:17:91:05:4c,dst=52:54:00:14:54:c6),eth_type(0x8100),vlan(vid=3,pcp=0),encap(eth_type(0x0806)),
>>> packets:2, bytes:120, used:0.014s, actions:pop_vlan,7
>>> I can't find any definitive documentation for an action element consisting
>>> purely of a number - in this case "7".
>> I have just re-read the man page, and found the following:
>> "The  target  may  be  a  decimal  port  number  designating the physical
>> port on which to  output the packet."
>> so the packet should, according to the above, be forwarded to port 7, which
>> is vnet0.
>> However, the packet is not arriving on vnet0.  Any ideas where I can look to
>> find out why not?
> I'd start by checking the kernel log (with "dmesg").

Hi Ben

I had already done system level debugging to try find out where issues 
may lie.  There are no kernel logs indicating dropped packets or 
transmit failures.

A diff between the contents of /sys/class/net/vnet0 (which is the port 
that gets no traffic) and /sys/class/net/veth-carbon1-3/ (which is the 
port that gets traffic) shows very few differences at the kernel level 
(rx/tx counts/address/etc differ, but type/features/carrier/flags/etc 
are the same)

What I know so far is that while openvswitch should be forwarding 
packets onto vnet0 (which is what the flow indicates), vnet0 does not 
receive those packets (as indicated with tcpdump).  Also the tx_packets 
counter for vnet0 does not increment (as it should when packets get sent 
to the interface and transmitted on)

Is this a kernel/openvswitch bug?  I can probably get the interface 
working by migrating the VM to a different host and migrating it back, 
but I would rather leave it in a non working state to try and pinpoint 
the issue.


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