In case of L3 agents being down on the dashboard , you can update the agent state by applying the solution suggested below.
ISSUE : Single L3 Agents has the state down on the horizon dashboard
SOLUTION : Restart the neutron server service on the controller node then restart openvswitch and openvswitch agent on the hypervisor of the affected node
ISSUE : All L3 Agents Are Down on the horizon dashboard
SOLUTION : Restart openstack-nova-network on the controller node and on the affected machine
Information you should know about this article
Openstack Version : Havana
Operating System : Centos 6.5