The event log shows repeated errors, perhaps 12 or so, multiple times per day. Here is a typical error with server name xx'd out.
The dynamic registration of the DNS record '_ldap._tcp.xxxxx.com. 600 IN SRV 0 100 389 DELL1420.xxxxx.com.' failed on the following DNS server:
DNS server IP address: 22.214.171.124
Returned Response Code (RCODE): 5
Returned Status Code: 9017
For computers and users to locate this domain controller, this record must be registered in DNS.
There are slight differences but each time, the IP address 126.96.36.199 is in there.
I do not recognize the DNS server IP address: 188.8.131.52 which appears in each. It's not the DNS address to which my NIC cards are set.
My connection goes thru a router with NAT. I can block that IP address but don't know if I should. Nor do I know how to check where that IP address originates.