The L3 agent is part of the openstack-quantum package.
Create a bridge "br-ex" that will be used to uplink this node running quantum-l3-agent to the external network, then attach the NIC attached to the external network to this bridge. For example, with Open vSwitch and NIC eth1 connect to the external network, run:
sudo ovs-vsctl add-br br-ex sudo ovs-vsctl add-port br-ex eth1
The node running quantum-l3-agent should not have an IP address manually configured on the NIC connected to the external network. Rather, you must have a range of IP addresses from the external network that can be used by Quantum for routers that uplink to the external network. This range must be large enough to have an IP address for each router in the deployment, as well as each floating IP.
sudo yum install -y openstack-quantum
Run the agent setup script:
sudo quantum-l3-setup --plugin openvswitch
Enable and start the agent:
sudo systemctl enable quantum-l3-agent.service sudo systemctl start quantum-l3-agent.service