rancherOS/assets/docker/cni/bridge.d/bridge.conf

{
    "name": "bridge",
    "type": "bridge",
    "bridge": "docker-sys",
    "isDefaultGateway": true,
    "ipMasq": true,
    "hairpinMode": true,
    "ipam": {
        "type": "host-local",
        "subnet": "172.18.42.1/16"
    }
}