I'm not sure I'm correctly following what you're asking for, but here is a snip from the openshift-ansible installer example inventory file for OCP v3.11 (You can check the other release versions on their respective branches as well). Here you can see a number of configuration variables around the SDN, including CIDR block ranges:
Reference: https://github.com/openshift/openshift-ansible/blob/release-3.11/inventory/hosts.example
# Configure SDN cluster network and kubernetes service CIDR blocks. These
# network blocks should be private and should not conflict with network blocks
# in your infrastructure that pods may require access to. Can not be changed
# after deployment.
#
# WARNING : Do not pick subnets that overlap with the default Docker bridge subnet of
# 172.17.0.0/16. Your installation will fail and/or your configuration change will
# cause the Pod SDN or Cluster SDN to fail.
#
# WORKAROUND : If you must use an overlapping subnet, you can configure a non conflicting
# docker0 CIDR range by adding '--bip=192.168.2.1/24' to DOCKER_NETWORK_OPTIONS
# environment variable located in /etc/sysconfig/docker-network.
# When upgrading or scaling up the following must match whats in your master config!
# Inventory: master yaml field
# osm_cluster_network_cidr: clusterNetworkCIDR
# openshift_portal_net: serviceNetworkCIDR
# When installing osm_cluster_network_cidr and openshift_portal_net must be set.
# Sane examples are provided below.
#osm_cluster_network_cidr=10.128.0.0/14
#openshift_portal_net=172.30.0.0/16
# ExternalIPNetworkCIDRs controls what values are acceptable for the
# service external IP field. If empty, no externalIP may be set. It
# may contain a list of CIDRs which are checked for access. If a CIDR
# is prefixed with !, IPs in that CIDR will be rejected. Rejections
# will be applied first, then the IP checked against one of the
# allowed CIDRs. You should ensure this range does not overlap with
# your nodes, pods, or service CIDRs for security reasons.
#openshift_master_external_ip_network_cidrs=['0.0.0.0/0']
# IngressIPNetworkCIDR controls the range to assign ingress IPs from for
# services of type LoadBalancer on bare metal. If empty, ingress IPs will not
# be assigned. It may contain a single CIDR that will be allocated from. For
# security reasons, you should ensure that this range does not overlap with
# the CIDRs reserved for external IPs, nodes, pods, or services.
#openshift_master_ingress_ip_network_cidr=172.46.0.0/16
# Configure number of bits to allocate to each host's subnet e.g. 9
# would mean a /23 network on the host.
# When upgrading or scaling up the following must match whats in your master config!
# Inventory: master yaml field
# osm_host_subnet_length: hostSubnetLength
# When installing osm_host_subnet_length must be set. A sane example is provided below.
#osm_host_subnet_length=9
.
