We have a NAS (Synology, running DSM 6) which is connected to our Active Directory on a Windows 2016 server. The NAS has 7 shared folders which are shared using SMB2.
When browsing to the NAS using Windows Explorer (tested on both Windows 7 and Windows server 2016) there is a delay for about 10 seconds before the shared folders are shown. It doesn't matter whether we use the name of the NAS (\\my-nas) or its IP-address (\\10.x.x.x).
While continously navigating the folders there is no delay.
Any ideas on why this is happening and how to fix it?
Update
I ran Wireshark and then started Windows Explorer. This is what the output looks like (I have filtered to just show my IP and the NAS's IP):
As you can see by the red rectangle there is about 8 seconds with total inactivity. This is after "Session Setup Request" is sent from the client (10.0.107.100) to the NAS (10.0.107.99), and before an answer, "Session Setup Response", is received.
Update 2
Did a new Wireshark session, in response to Michal Sokolowski's comment, and this time also included the traffic for our domain server (10.0.0.98). Now some UDP traffic on port 53 (shown as "DSN" protocol) and on port 137 (shown as "NBNS" protocol) is visible:
Update 3
I installed Wireshark on the domain server (10.0.0.98) to see the entire communication with the NAS:
(The image shows just an excerpt: Full Wireshark log for 'Update 3')
The line selected in the image, number 402, is just before a 3 second delay. This happens once more later on with the exact same messages.
Is it possible to say something more given this information?