I host a free mumble server on one of my servers running Windows Server 2012 R2 at home in Tokyo. I have an amazing 1GBps internet connection & I like being able to share that with people. A while back I did some hardware upgrades to my server including upgrading the network card to a dual intel card so I could do link aggregation. After doing this I noticed that there was a issue with the mumble server murmur logs. I was getting this error over & over again.

=> Registration failed: SSL handshake failed
=> Registration: SSL Handshake error: The issuer certificate of a locally looked up certificate could not be found
=> Registration: SSL Handshake error: The root CA certificate is not trusted for this purpose

My server was also no longer listed as a public free mumble server & I thought I may have caused this when I updated mumur to the latest version a month ago & not noticed the error. So after jumping to that conclusion I spend a while researching the error. Everything I found online didn’t actually help or point me into the right direction. So i slept on it for a few days & just waited for my brain to think out side of the box. It happened while I was sitting in Starbucks enjoying a latte & I was just thinking about the issue when I realised it must be because of the network interface upgrade. When I got home I cross referenced my settings from the onboard NIC with the new aggregated Intel NIC & realised I had IPV6 disabled on the old one but the new one I had it enabled. I don’t have a need for IPV6 so I turned it off  & restarted murmur & the error completely disapeared.

So if you are getting this error disable IPV6 on your Network adaptor. If you require IPV6 then you will need to do some research into how to get murmur to work with it.

I hope this helps & points you in the right direction for this error message.