By default, the network options are in the install-config.yaml file. See Step 4, substep h in Preparing and running the Ansible playbooks.
The following sample code shows CNI information in the install-config.yaml file:
- cidr: 10.128.0.0/14
Ignition configuration files are created from the information that you define in the install-config.yaml file by using the openshift-install binary file. Creating ignition files is described as a play in the Ansible playbooks. For the specific steps to perform the task, see this .