Windows 7 losing Internet Connection

At work we use Zentyal with DHCP and DNS services as default gateway for our local network. Everything works fine with Linux and Windows XP clients, but Windows 7 clients from time to time lose WAN connection, but, interestingly, not LAN connection! Event viewer shows that "DNS server is not responding", although correct IP address for DNS server is specified.

After exausting investigatigation, I have found that Windows 7 have problems with ARP resolution. Since Zentyal has two ethernet cards, one for local and other for Internet connection, checking arp table with arp -a shows that from time to time default gateways IP address is asociated with MAC address of external NIC on Zentyal. Because of this Layer 2 issue, DNS service is not responding until, by some misterious reason, arp table is again populated with physical address of internal NIC.

Quick-fix is to statically join correct MAC addres with IP address of default gateway on Windows 7 clients, like this (fill in your gateway´s MAC address):

netsh interface ipv4 add neighbors "Local Area Connection" 192.168.1.1 00-06-4f-03-d2-75 

Problem solved!

If you want to remove static arp entry:

netsh interface ipv4 reset