** Description changed:
[Impact]
On an ML2/OVS deployment with tunneling disabled
(enable_tunneling=False, flat/vlan type drivers, no br-tun), neutron-
openvswitch-agent crashes on every restart:
ERROR neutron...ovs_oskenapp Agent main thread died of an exception:
AttributeError: 'NoneType' object has no attribute 'get_flood_to_tun_ofports'
File ".../ovs_neutron_agent.py", line 342, in __init__
self._restore_local_vlan_map()
File ".../ovs_neutron_agent.py", line 520, in _restore_local_vlan_map
tun_ofports = self.tun_br.get_flood_to_tun_ofports(local_vlan)
AttributeError: 'NoneType' object has no attribute
'get_flood_to_tun_ofports'
_restore_local_vlan_map(), called from OVSNeutronAgent.__init__(), calls
self.tun_br.get_flood_to_tun_ofports() for every integration-bridge port
carrying other_config:net_uuid, without checking whether tunneling is enabled.
With tunneling disabled self.tun_br is None, so the call raises.
The call sits behind "if net_uuid:", and an integration-bridge port only
carries net_uuid in its OVS other_config after the agent has written it
during normal operation:
1st start: ports have NO net_uuid -> skipped -> OK
restart: ports HAVE net_uuid -> called -> crash
Because the crash happens in __init__, the agent never reaches rpc_loop and
never reprograms OVS flows, so instances on the node lose provider-network
connectivity until manual recovery.
Clearing net_uuid by hand recovers the agent once, but the agent rewrites it
during operation and the next restart crashes again:
ovs-vsctl remove Port <integration-bridge-tap-port> other_config net_uuid
systemctl restart neutron-openvswitch-agent
[Test Plan]
Deploy ML2/OVS with tunneling disabled on the target release:
# /etc/neutron/plugins/ml2/ml2_conf.ini
[ml2]
type_drivers = flat,vlan
tenant_network_types = vlan
mechanism_drivers = openvswitch
# /etc/neutron/plugins/ml2/openvswitch_agent.ini
[ovs]
- enable_tunneling = False
bridge_mappings = physnet1:br-data
+
+ [agent]
+ tunnel_types =
+
+ enable_tunneling is not a config option: the agent derives it as
bool(tunnel_types), so leaving tunnel_types empty is what disables tunneling
and leaves self.tun_br as None.
+ Confirm no tunnel bridge was created:
+
+ ovs-vsctl list-br
+
+ There must be no br-tun in the output.
Boot an instance on a flat or VLAN provider network so that the agent
writes net_uuid into the integration-bridge port, then confirm the ports
carry it:
ovs-vsctl --columns=name,other_config list Port | grep net_uuid
Before the patch (reproduce the crash):
systemctl restart neutron-openvswitch-agent
journalctl -u neutron-openvswitch-agent -n 50
Expected (buggy) result:
AttributeError: 'NoneType' object has no attribute
'get_flood_to_tun_ofports'
and the agent stays down.
After the patch (confirm the fix):
- # install neutron-openvswitch-agent from -proposed
+ # install neutron-openvswitch-agent from -proposed, then record the
version
+ apt-cache policy neutron-openvswitch-agent
systemctl restart neutron-openvswitch-agent
systemctl is-active neutron-openvswitch-agent
journalctl -u neutron-openvswitch-agent -n 50
openstack network agent list --agent-type open-vswitch
Expected (fixed) result:
* The agent restarts without the AttributeError and reports active.
* The agent shows alive/UP in "openstack network agent list".
* Existing instances keep provider-network connectivity across the restart.
* On a tunneling-enabled (VXLAN/GRE) deployment, restarting the agent still
restores the br-tun flood output ports, so east-west traffic between compute
nodes continues to work.
[Where problems could occur]
If the enable_tunneling guard is evaluated incorrectly on a tunneling-
enabled deployment, the br-tun flood output ports are not restored on
agent restart and broadcast or unknown-unicast traffic on tunnel
networks either stops reaching remote compute nodes or is flooded to the
wrong ports.
[Other Info]
Fixed upstream on master and stable/2026.1 (neutron 28.0.1) by
https://opendev.org/openstack/neutron/commit/0b06dc038b685f3340c8a7cf7b07128ed5c39b27
Guard tun_br in _restore_local_vlan_map when no br-tun
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https://bugs.launchpad.net/bugs/2156566
Title:
neutron-ovs-agent crashes on restart with tunneling disabled (tun_br
is None)
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