From undercloud node, which IP address should set to DNS server?

Issue

• https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux_OpenStack_Platform/7/html-single/Director_Installation_and_Usage/index.html

3.9. SETTING A NAMESERVER FOR THE OVERCLOUD

Overcloud nodes require a nameserver so that they can resolve hostnames through DNS. The nameserver is defined in the Undercloud’s neutron subnet. Use the following commands to define the nameserver for the environment:
$ neutron subnet-list
$ neutron subnet-update [subnet-uuid] --dns-nameserver [nameserver-ip]
View the subnet to verify the nameserver:
$ neutron subnet-show [subnet-uuid]
+-------------------+-----------------------------------------------+
| Field             | Value                                         |
+-------------------+-----------------------------------------------+
| ...               |                                               |
| dns_nameservers   | 8.8.8.8                                       |
| ...               |                                               |
+-------------------+-----------------------------------------------+

• In the document, the dns server should set for the overcloud, but which ip address should used, local_ip, undercloud_public_vip or undercloud_admin_vip?