kubespray/roles/network_plugin/flannel/defaults/main.yml

---
# Flannel public IP
# The address that flannel should advertise as how to access the system
flannel_public_ip: "{{ access_ip|default(ip|default(ansible_default_ipv4.address)) }}"

## interface that should be used for flannel operations
## This is actually an inventory node-level item
# flannel_interface:

# You can choose what type of flannel backend to use
# please refer to flannel's docs : https://github.com/coreos/flannel/blob/master/README.md
flannel_backend_type: "vxlan"