neutron

What is the use of the Dead VLAN tag 4095 on quantum openvswitch plugin?

Asked by Vangelis Tasoulas

When I run "ovs-vsctl show", sometimes I see some ports with VLAN tag 4095

After doing some search I couldn't find much references on it except the source file "ovs_quantum_agent.py" which looks like this:

# A placeholder for dead vlans.
DEAD_VLAN_TAG = "4095"
...
...
def port_dead(self, port):
        '''Once a port has no binding, put it on the "dead vlan".

        :param port: a ovs_lib.VifPort object.'''
        self.int_br.set_db_attribute("Port", port.port_name, "tag",
                                     DEAD_VLAN_TAG)
        self.int_br.add_flow(priority=2, in_port=port.ofport, actions="drop")

The question is why '''Once a port has no binding, put it on the "dead vlan" and not destory it?

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Salvatore Orlando
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yong sheng gong (gongysh) said : 		#1

I think it is just for the sake of 'safety'. we don't want the quantum components to make mistake. but I am not sure.

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Best Salvatore Orlando (salvatore-orlando) said : 		#2

Every port on the integration bridge which cannot be mapped to a neutron port, and is therefore unknown to neutron, is put on this vlan, thus avoiding this port cannot snoop or generate traffic on tenants' networks.

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Vangelis Tasoulas (cyberang3l) said : 		#4

Thanks Salvatore, it makes sense now.