This particular issue made my life miserable for over a 2 week period and affected 3 of my backup servers! So what would happen is that, randomly some of my backup servers would somehow lose connection and drop of the network. I mean they would still be pingable and online however when I would try to login, I would get a "No logon servers available" message and at that point the only way to fix this was to restart the server! This made my backups to fail as well. I have like over 50 Tb to backup on each of my locations and because of this issue they would never complete. So after digging around I found a couple of warning messages in my System log as you see below.
So looks like my backup servers were getting their TCP connections exhausted and hence would drop connections to the DC and the general connectivity was affected as well.
- I opened up my iSCSI initiator on the server and noticed a redundant LUN stuck in a reconnecting state. I had introduced a lun from my Netapp to this server to act as a D drive, on which I have my Netbackup installation. So I removed that reconnecting lun from the iSCSI window as it was no longer needed and also removed it from my Favorite targets window within the iSCSI initiator window.
- After that just to be safe I modified some registry entries as well to increase the TCP buffer, I dont think his was necessary after I fix the reconnecting LUN in the iSCSI initiator but I was fed up with my backups not completing so I put these keys in anyways.
Go to HKLM\System\CurrentControlSet\Services\Tcpip\Parameters and under that make 4 DWORD vaules as you see below and restart the server!
Once you do this, hopefully the server will no longer lose the TCP connection and you will not get the "No Logon Server Available" message when you try to logon. I believe this was an affect of a Microsoft patch that was released recently as I have read this online. I am sure what the patch was or the number though.
Hope this helps!