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Note that I have also cross posted this to Synology forums. I'm posting here because I'm not sure if the problem is with Windows or with the Synology server:

Background

Dozens of workstations with several Synology servers.

All workstations running Windows 10 Pro.

For the past year, and up until about a week ago, all workstations were able to access all Synology servers fine.

Problem and Symptoms

Now just starting about one week ago, ONE workstation is unable to access ONE Synology server via Windows Explorer.

It doesn't work with \\UNCname nor with \\ip.ad.re.ss

However, I can ping the server just fine using the ip.ad.re.ss and nslookup for UNCname returns the correct address.

Conundrum

If this were happening to all my workstations, I'd assume the Synology server was at fault. But all the other workstations have no problem accessing this one Synology box. If this were happening with all Synology servers on this one machine, I'd assume the workstation was at fault. But the workstation has no problem accessing the other Synology boxes on the same network, and up until a week ago had no problem with the specific box in question.

Again, it is just the ONE workstation suddenly having problems with ONE Synology server.

Nothing has changed on my end, except of course that there are automatic updates for both Synology and for Windows 10... so again I have no idea where the problem lies.

wazoox
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Daniel
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  • Did you compare updates applied to both the Synology servers and also between 2 workstations experiencing different behavior? You can use the Get-Hotfix or Get-WindowsPackage PowerShell cmdlets on Windows 10 to list what has been applied. – twconnell Oct 13 '17 at 07:30

4 Answers4

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There are a number of things you can check... that might give you more insights into what is going on.
Ping can be a useful tool, but can also give you many false-positives.

  • Have you looked at the arp table and made sure that the mac-address matches the device? Maybe something else has hijacked the mac-address, or a duplicate IP in the network.
  • Are you dropping any packets? Maybe you have a bad cable or ethernet port (on switch or device).
  • Have you compared the subnet mask? maybe you have the wrong mask, and are outside the subnet.
  • Have you tried connecting to other network shares? Maybe there is something borked with the network stack on that machine.
  • Have you looked at the windows firewall? Maybe it is blocking access to the device because you are in a "public" zone instead of "domain" or "private".
  • Have you tried connecting to other services on the synology? ... last I checked, they also respond to http/https? Maybe being able to connect to other ports on the device might give you additional info.
  • Have you updated network drivers on that device? Perhaps you're using an old broken driver.

... the list continues.

TheCompWiz
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  • Network card: all other functions are fine like file sharing and web browsing. Network shares: connects to other Syn file shares with no problem. Other services: can connect to web interface via http/https no problem. ARP table: if problem here, I couldn't connect via http. Subnet mask: assigned by Windows AD DHCP server, if problem here ping and http would not work. Firewall: if problem here could not connect to other Syn shares. Driver: no updates have been done unless through Windows update, shares have been working fine for a year. – Daniel Oct 11 '17 at 17:06
  • Have you tried mapping a share using a command-prompt? `net use x: \\blah\blah`? You might get more debug info. – TheCompWiz Oct 12 '17 at 16:59
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    That did it. `net use` informed me the connection could not be made because it was insecure. Specifically the Synology server was requesting an SMB1 connection, and Windows would only allow SMB2. I checked the Synology settings and sure enough it was only allowing SMB1 (not sure why since I have many Synology boxes, and all allow SMB2 and I would never touch those settings but whatever). After changing the setting on the Synology box, every thing started to work fine. – Daniel Feb 14 '18 at 13:59
  • Even stranger that I only had this problem with *ONE* user on *ONE* machine (after further investigation, other users logging onto the same machine had no problem accessing the share) and all the other users and Windows machines on the *SAME* network accessing the *SAME* server and the *SAME* share had no problems. I mean, it *makes sense* that Microsoft would release a patch disabling SMB1 access if it is insecure. It *doesn't* make sense that only one user on one machine was having this problem. – Daniel Feb 14 '18 at 15:15
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For this exact situation, I solved it by going to "Turn Windows features on or off" and ensuring that all three options under "SMB 1.0/CIFS File Sharing Support" were checked.

nmit026
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I suppose that the Windows 10 Pro computer can open the DSM website of the culprit Synology in a browser (http://ipaddress:5000 or https://ipaddress:5001), but fails to connect to the Synology fileshare in Windows Explorer?

What is the mininal and maximal SMB protocol set in the Synology box (Control Panel > File Services > SMB/AFP/NFs tab > Advanced Settings? Any other Advanced settings out of order, compared to the other Synologies?

Something to look at: years ago it was necessary to lower the Windows NTLM authentication on the workstation to a less secure level to be able to connect to a Synology fileshare using Windows Explorer. I can't find the specific settings for now, but google for it.

Victor Vogelpoel
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  • You're referring to the LmCompatibilityLevel (https://technet.microsoft.com/en-us/library/cc960646.aspx) – twconnell Oct 13 '17 at 07:24
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Thanks to @TheCompWiz, using net use from the command line gave me a more detailed error message, indicating that Windows could not access the share for security reasons as SMB1 access is deprecated and the server was only allowing SMB1 connections (not sure why). After changing the server settings to allow SMB2 connections, the problem was fixed.

I'm also not sure why I only had this problem on one machine and only one user, and all other machines were able to access the share with no problem when they are all running the latest version of Windows 10 Pro. But I'm not going to worry about that right now - everything is working fine.

Daniel
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