Neutron uses default settings to determine the type of routers that tenants are allowed to create as well as the number of routers that should be deployed across L3 agents.

The following default settings are specified within the Neutron configuration file at /etc/neutron/neutron.conf and only need to be modified on the host running the Neutron API service. In this environment, the neutron-server service runs on the controller node:

# =========== items for l3 extension ==============
# Enable high availability for virtual routers.
# l3_ha = False
#
# Maximum number of l3 agents which a HA router will be 
# scheduled on. If it is set to 0 the router will be scheduled on
# every agent.
# max_l3_agents_per_router = 3
#
# Minimum number of l3 agents which a HA router will be 
# scheduled on. The default value is 2.
# min_l3_agents_per_router = 2
#
# CIDR of the administrative network if HA mode is enabled
# l3_ha_net_cidr = 169.254.192.0/18
# =========== end of items for l3 extension =======

To set HA routers as the default router type for tenants, set the l3_ha configuration option to True in neutron.conf. For this demonstration, the default value of false is sufficient.

When an HA router is created, multiple router namespaces are created and distributed among the L3 agents. At a minimum, two L3 agents are required.

To increase the number of L3 agents required for redundancy, increase the min_l3_agents_per_router value. For this demonstration, the default value is sufficient.

To set a maximum number of L3 agents used for a virtual router, set max_l3_agents_per_router accordingly. For this demonstration, the default value is sufficient.

Once the changes have been made, restart the neutron-server service on the controller node for the changes to take effect.