How to do it...

1. Update the group_vars/core.yml file with the following data to define core links between core switches and WAN routers:

core_l3_links:
  core01:
    - name: Ethernet1/0
      description: wan01_Gi2
      ipv4: 10.3.1.0/30
      ospf: yes
      ospf_metric: 100
      peer: wan01
  core02:
    - name: Ethernet1/0
      description: wan02_Gi2
      ipv4: 10.3.1.4/30
      ospf: yes
      ospf_metric: 200
      peer: wan02

2. Update the pb_build_network.yml playbook with the following tasks to set up OSPF:

- name: "PLAY 2: Configure Core Switches"
  hosts: core
  tags: l3_core
  tasks:
< -------- Snippet -------- >
    - name: "P2T9: Configure OSPF On Interfaces"
      ios_config:
        parents: interface {{ item.name }}
        lines:
          - ip ospf {{ ospf_process }} area {{ ospf_area }}
          - ip ospf network point-to-point
          - ip ospf cost {{item.ospf_metric | default(ospf_metric)}}
      loop: "{{ (svi_interfaces + core_l3_links[inventory_hostname]) | selectattr('ospf') | list }}"
    - name: "P2T10: Configure OSPF Passive Interfaces"
      ios_config:
        parents: router ospf {{ ospf_process }}
        lines: passive-interface {{item.name}}
      loop: "{{ (svi_interfaces + core_l3_links[inventory_hostname]) | selectattr('ospf','equalto','passive') | list }}"