---
- name: Ensure that default and custom tables names don't overlap
  assert:
    that: "not (iproute2__default_tables.keys()
                | intersect(iproute2__custom_tables.keys()))"

- name: Configure rt_tables
  template:
    src: rt_tables.j2
    dest: /etc/iproute2/rt_tables
    owner: root
    group: root
    mode: u=rw,g=r,o=r
  vars:
    iproute2__tables: "{{ iproute2__default_tables
                          | combine(iproute2__custom_tables) }}"
...