They are here:
The DNS answers file has specific entries detailing the answers to be provided to each querying container Rancher is aware of (and controls). Containers running outside of Rancher cannot query this server. The Rancher External DNS server can be used to overcome this.
Containers using host-mode networking, using the
io.rancher.container.dns: true label will receive the answers detailed in the «default» section.
DNS services are provided by the Rancher DNS server which runs on each host in the Network Agent container.