Today we have been alerted by the network support guys about high memory consumption in the firewall (FortiGate 100F) that could lead to it entering safe mode.
We searched the logs and found a truckload of DNS queries from the clients to the primary domain controller's SRV record (_ldap._tcp.pdc._msdcs.ourcompany.local), repeated to the tune of one every 15-20 seconds, per client. See linked screenshot.
I don't know how long this has been going on. Our systems are working perfectly fine Active Directory wise, and I'm not aware of any reason this could happen, or even if it should happen... but given that it eclipses other DNS traffic, I thought it was worth a look.
Weird thing is that this is happening just on PC's on the clients' subnet. Machines on other subnets, including ours, don't display this behavior. Other than that, GPOs are the same for everyone; firewall access policy to the DC is the same for everyone (just created a test rule to be sure). We have NetBios turned off through DHCP. Machines are all Windows 10 Pro updated to 2004 or newer, domain controller is 2012 R2.
Can someone shed a clarifying light on this? Thanks!
