Reason for the below failure:

The Active Directory Domain Services Installation Wizard (Dcpromo) was unable to establish connection with the following domain controller. 

 
Domain controller:
winad01.mds.xyz 
 
Additional Data 
Error value:
8524 The DSA operation is unable to proceed because of a DNS lookup failure.

and the subsequent failure in Promotion of a Server to an Active Directory Domain Controller was due to the two nics on each host having DNS settings other then 127.0.0.1.  Two nics were present, one was a LAN and the other NLB on each host.  Once fixed, AD DC promotion went along further but still failed.

This ended up being a DNS issue between the two AD DC's.  First AD DC had a DNS server as well so had to have itself as a DNS server.  So enter first DNS server's IP into the DNS 1 field and enter the router's (usually 192.168.0.1) into DNS 2 field.

Likewise for DNS 2.  Enter the IP of the second DNS server into the NIC DNS 1 field of this second DNS / AD DC server.  DNS 2 should be the main router 192.168.0.1

DNS / AD DC 1:
IP: 192.168.0.123
DNS 1: 192.168.0.123
DNS 2: 192.168.0.1

DNS / AD DC 2:
IP: 192.168.0.124
DNS1: 192.168.0.124
DNS2: 192.168.0.1

Cheers,
TK