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Sometimes losing DNS when changing ISP's

Posted on 2008-06-25
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Last Modified: 2012-08-14
I have 3 Win XP machines connected to a router, which I connect to one of three ISP's (I'm overseas, so sometimes an ISP is not working very well).   All 3 machines are set up with the LAN to use DHCP to set the IP and to automatically get a DNS server.  All are using ZoneAlarm Security Suite.  This works fine always on 2 machines, and usually on one of the others -- i.e. I can switch ISP's, do the "Repair" on the connection, and then continue working.  

However at times this one machine (and this one only)  will be unable to resolve names tho it has internet connection -- I can't get to any website via DNS.  Sometimes if I disable the LAN and shut down browsers/Skype/... the problem will get resolved when I enable the LAN again.  But oftentimes, that doesn't work.  The only thing left that fixes it is rebooting, which is something I'd rather avoid.

So I'd like to know a way around rebooting when this does happen, or at least to understand the cause of the problem and perhaps some ways to avoid it.  
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Question by:BaliDave
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Author Comment

by:BaliDave
ID: 21873492
upping points
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Accepted Solution

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Rob Williams earned 500 total points
ID: 21878104
You could write a little script/batch file to put on the desktop that will get new connection information and flush all name cache's.

ipconfig  /release
ipconfig  /renew
ipconfig  /flushdns
nbtstat  -R
exit

The ideal answer would be to add a Windows 2003/2008 server running DNS, and add the different ISP's as forwarders.
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Author Comment

by:BaliDave
ID: 21879240
OK, I'll try that next time it happens.  BTW, I usually do a ipconfig /renew in attempting to clear up the problem, but not the others.  Perhaps the /flushdns will do that.

I'll report back when it happens again..  Thanks for the tip.
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Expert Comment

by:Rob Williams
ID: 21879449
Let us know how you make out.
--Rob
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Author Comment

by:BaliDave
ID: 21897337
Well sorry to say that didn't work.  DNS is still hung so I'll reboot.  I REALLY don't want to add another machine in my already too complex set up here.  If anyone has any other ideas, please let me know.  

Thanks anyhow.
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Assisted Solution

by:Rob Williams
Rob Williams earned 500 total points
ID: 21898519
Sorry, no other suggestions.
By the way, the way this is usually handled is to change to a dual WAN port router that supports fail over protection. These units connect to both ISP's and if one is down they automatically route the traffic through the working port. The router has the DNS information for both connections and the PC's just point to the router for DNS. There are quite a few available. Two are the Linksys RV042 and the Netgear FVS124G, both of which are under $200
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Author Comment

by:BaliDave
ID: 21903435
Thanks.  But the new router solution won't work for me -- the problem I have is not that the ISP's die (I have 3 of them by the way), but that they start getting slow/unreliable or unusable with things like Skype.  So I decide when to switch and then just connect one of the three cables to my router, do a repair, and proceed.  (I'm in Indonesia and the internet situation is FAR behind most other places -- the fastest connection I can practically get is 512KB nominally tho often more like 50KB.  Plus it's expensive.)

Anyhow I'll leave this question open for a few more days in hopes of some other ideas.  And I'll keep playing with that machine and see if I can find some magic incantation that'll make it recover DNS capability when this happens.  Thanks for the suggestions tho.
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Expert Comment

by:Rob Williams
ID: 21903530
You are very welcome, I understand your predicament. Hopefully someone else will have other suggestions.
Good luck with it.
--Rob
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Author Comment

by:BaliDave
ID: 21931685
Well it looks like the solution has to do with disconnecting a Skype phone I have on that machine.  Apparently the driver on that was somehow preventing Windows from getting new DNS service at times (tho not always!?!?).  So disconnecting it and then doing at least the Repair now allows it to restore DNS service and then I reconnect the phone.  

Thanks everyone for the input anyhow.
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Author Closing Comment

by:BaliDave
ID: 31470873
Really the answer as I finally found, was disconnecting the Skype phone, but I think these commands can help others with similar problems.
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Expert Comment

by:Rob Williams
ID: 21932480
Ah! interesting, glad to hear you have it sorted.
Thanks BaliDave.
Cheers !
--Rob
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