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Win 2008 server lost access to network router

Posted on 2016-08-03
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Last Modified: 2016-08-03
Have a Win2008 server in a small LAN. It is running as a domain controller and is also running an email server. LAN is connected to Internet via a ZyWALL router (192.168.1.1), and it has worked well for a long time. Yesterday I noticed that the server seemed to not access the Internet anymore (mail server failed dns lookups to external dns). Inbound emails work fine (the server responds to external requests).

Investigation showed that the server doesn't "see" the router.
I'm able to ping the router from other devices in the LAN. From the server I'm able to ping all other addresses - except the router address. From PCs in the LAN I'm able to ping the server's IP address. This tells me that there may be something that prevent the server to access the router. Have checked the routing tables, and the address 0.0.0.0 is routed to the correct address (192.168.1.1).

Expect that there may be some process or service that prevents the server from accessing the rouer's IP addres, but I'm not able to fine what it is. The server is running Malwarebytes to prevent attacks and malware. Have tried to disable it, but not sure if I've done it right.

Are there any other steps to take in order to solve this problems?  Thanks!
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Question by:Olaf Berli
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by:Michael Pfister
Michael Pfister earned 250 total points
ID: 41740604
When the server responds to external requests there is IP connectivity between the router and the server.

Anything on the ZyWall preventing access to the Internet just for the server?
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Author Comment

by:Olaf Berli
ID: 41740761
I can't see anything on the ZyWall that should create this problem. Have made a short log on it while running a ping on the server. It seems like the router sees the request, but doesn't respond. Have attached a screendump from Wireshark that displays the router log file.
wireshark.pdf
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Lee W, MVP earned 250 total points
ID: 41740826
Perhaps it's not the server that's the problem. What if your router thought it was being attacked from the server and disallowed communication with it.  

Have you tried a different router - even a cheap home one - just to test...?
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Author Comment

by:Olaf Berli
ID: 41741230
Good idea!  Put in an older ZyWall 2+ and it works just as it should. Server pings the router ok and the server is able to access the internet. Need to find out why that other ZyWall didn't respond.... Haven't seen any setting that should "ban" local units....  Anyway - thanks a lot!
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Author Closing Comment

by:Olaf Berli
ID: 41741234
Thanks!
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