[ovs-discuss] Traffic loop problem, when a controller is setted

MIGNINI FABIO d037918 at polito.it
Tue Mar 17 17:57:58 UTC 2015


I have noticed an unexpected generation of traffic loop 
using a very simple configuration of KVM and OVS.
In particular the configuration that trigger the problem 
is the one listed below:

    | Virtual machine |
         |       |
  |                     |
  |     OVS Bridge      |

The OVS Bridge has two ports that are connected to the 
virtual machine. Within the virtual machine there is a 
linux bridge that bridges both the vm's interfaces.
I found the problem with two different configuration of 
the bridge:
	- setting an existing OF controller (OpenDaylight)
         - setting a fake address for the OF controller (a 
not reachable IP address)

This is the output of the 'ovs-vsctl show' command (I 
provide here only the second configuration, as you can see 
the controller is not connected):

root at controller:~# ovs-vsctl show
     Bridge br-int
         Controller "tcp:"
         Port br-int
             Interface br-int
                 type: internal
         Port "vnet1"
             Interface "vnet1"
         Port "vnet0"
             Interface "vnet0"
     ovs_version: "2.3.1"

The only flow in the OVS bridge "br-int" is a DROP flow, 
without any match (inserted manually before the starting 
of the virtual machine).
This is the output of the 'ovs-ofctl dump-flows br-int' 

root at controller:~# ovs-ofctl dump-flows br-int
NXST_FLOW reply (xid=0x4):
  cookie=0x0, duration=232.952s, table=0, n_packets=0, 
n_bytes=0, idle_age=232, priority=1 actions=drop

With this configuration I was expecting that all the 
traffic will be dropped by the OVS Bridge (as happens when 
no controller is setted).
Instead a traffic loop is generated between the two ports 
in the bridge.
It seems that the DROP flow rule is not working as 

Any suggestion?

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