Every day losing SMB/Internet connection for 10 minutes at same time


For the past weeks we experience the following problem at our company. Every day at 11:00 am clients (Windows 7 Pro) lose their netwerkshares and Internet connections. It could be more often, but users are not really clear about that.

But it is a fact that it happens at least every day at that specific time for 10 minutes. When it's 11:10 am all network connection are restored automatically.

The past days I logged on into a machine and noticed the following:
I was logged on with RDP on a PC and the server at 11:00 am and access to network shares/Internet got lost from the PC. Network shares and Internet was not lost on the server.
I started two ping requests to our server: 1 on IP base and 1 on hostname. During the time I couldn't access the Samba shares and Internet I get time-outs on both ping requests. When I get respone again after 10 minutes Samba/Internet connections are restored automatically.

- During the connection loss I maintain the RDP session with good latency from WAN to the SBS2011 server and random PC
- I checked all tasks in task scheduler, but can't find any tasks planned at this specific time
- I checked all logs (Appliction/Security/Setup/System) but can't find anything getting logged every day at that time
- System resources were widely available: 14GB of RAM out of 32GB total, less then 10% CPU usage and very little NIC usage
- During that time no back-ups or other known tasks run

The following roles are installed:
- Active Directory Certificate Services
- Active Directory Domain Services
- Print and documentservices
- Fileservices
- DHCP Server
- DNS Server
- Remote desktop services
- Service for networkpolicy and access
- Applicationserver
- Webserver (IIS)

At the 8th of March I installed availble Microsoft updates (I do this every month), but I allready did a rollback of those updates and this didn't resolve the problem. The following SharePoint updates were also installed, but I cannot uninstall those:


Can somebody please assist me in solving this problem? Thanks very much in advance.
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To resolve this, you might want to isolate the servers and only one PC for testing purposes. Cut off everyone at 11am and see it the PC still has access to resources. What sort of network switches do you use? Perhaps an STP issue on your network caused by a client or clients?
sargesearAuthor Commented:
To cut off everything else I'll have to try this on a sunday.. Switches we use are HP1810 series. I don't know if we have STP available on our types; have to find that out.

But isn't it weird that (for example) RDP sessions work great when this problem occurs?
andreasSystem AdminCommented:
can clients access other server at that time or is only the connection to this server disturbed? Does internet/email to external servers work during that time?

Does anything is in the system logs (event viewer) at 11 o clock on the server and clients that try to access?

You should try a packet capture of a session from a client to the server at 11 this can be tried when others still working, only if no success or to much is going on you can try it when there is only the server and one client on the net.

Really only one clinet and the server also no IP phones, printers, ect. pp. move them to a new vlan or connect them to a small private switch for testing.
sargesearAuthor Commented:
We found it out; it was the ESET Endpoint Security firewall which blocked certain ports at this time when updating itself through the organization with ERA. We uninstalled this unnecessary internal firewall and installed Endpoint AntiVirus on every client >> problems are gone!

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sargesearAuthor Commented:
It solved all problems
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