Got a email from one of our co-managed IT / Tier3 / managed RMM clients that was having issues with DNS resolution. The network consists of a Synology NAS acting as Domain Controller / DNS Server and a VM on the Synology that runs the clients main application. Several of the workstations were having an issue where they could not browse to the IP address (\\192.168.0.11\sharename)of the application server at one time and could not browse to the UNC path (\\servername\sharename) of the same server on another day. First tried setting the external forwarders to Google DNS and the Forward Policy to Forward First, but the problem resurfaced. So we dug deeper into the DNS settings and found the following:

If you look closely the IP address of the server is 192.168.0.11 and the records for DNS servers associated with the domain above and below it point to servers outside the subnet of the application server (10.0.0.2). Upon further investigation this DNS server address was blocked by the firewall because it was an old IP address scheme that was no longer in use. The current good DNS server IP addresses are 192.168.40.10 and 192.168.0.10.

Turns out the stale DNS records were the problem. Made the needed changes to the DNS records and things are working great.

If your company needs a little extra help running the IT department, then contact us to setup a co-managed IT evaluation.