A DNS server is only necessary when configuring an OPC UA client and using a hostname instead of an IP address as the endpoint URL on the client (the URL to the OPC UA server).
Since the OPC UA client is not supported on the PK controller, DNS is not needed and therefore not supported on the PK controller. Also, because the OPC UA server on the PK controller only responds to incoming requests, it does not resolve hostnames and therefore does not require DNS.
The IPv4 default gateway address for the PK controller is set to the x.x.x.1 IP address of the PO1's primary device network's subnet for that particular controller. This means the x.x.x.1 IP address is reserved for the default gateway address. If the PO1's primary device network is using the x.x.x.1 address, then the default gateway is disabled. Also, a disabled network (configured as all zeros) does not have a defined default gateway address.
Redundant IPv4 default gateways are not provided; therefore, the secondary device network does not have a default IPv4 gateway address.