Here's a crazy one for you...
Windows Server 2016 Hyper-V host with a single guest, a Windows SBS 2011 server.
Everything was working fine for years, until suddenly a few weeks ago the internet started getting progressively worse for the users on the network (so they say).
One of the employees called the ISP, they thought the levels were bad on the modem, tech comes out, replaces the modem but the internet still isn't working. Hooks up his laptop bypassing the router and it's fine.
To shortcut hours of diagnostics I came to the cause and it's the first time I've seen this:
- If Windows Firewall is turned on, on the SBS 2011 guest, the internet will break for everyone.
- If Windows Firewall service is turned off, on the SBS 2011 guest, the internet is fine for everyone.
Now before someone thinks DNS, when I say the internet is 'broken' I...