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Switch router and ISP with WIndows 2008 R2 server.

Posted on 2011-03-11
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Last Modified: 2013-12-14
Currently have Windows 2008 R2 server with DC,DHCP and DNS configured. Currently using Qwest DSL internet service with ActionTec modem/router. Attempting to switch to new Mediacom Business internet service with Cisco WRVS440N router. Qwest and Mediacom DNS Forwarders are entered in DNS on server and resolve correctly when connected to ActionTec. Both routers are configured to same IP because we have static IP's on numerous workstations. Only have one router connected at a time. When new router is connected cannot ping router or resolve DNS addresses in Forwarders screen. If I go to a workstation and replace DNS address for Domain server to ISP's DNS servers I can browse internet. Seems to be DNS issue with Windows 2008 R2. Appreciate you suggestions.
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Question by:pmcgovern
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by:Scovndrel
ID: 35112971
It is most likely an ARP cache problem. Both routers have the same IP address. Windows associates that IP address with the MAC address of one router. You swap them and suddenly the MAC is different. Windows does not notice this.

Use this command:  arp -d (enter)

Then try pinging again. The arp cache will timeout by itself so you don't have to do this on all workstations.

Also suggest you remove the DNS forwarders entirely and let the DNS server use its root hints. That removes a single point of failure at your ISP's DNS server.
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Author Comment

by:pmcgovern
ID: 35140479
THanks. Will be back at site later this week and will try.
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Author Comment

by:pmcgovern
ID: 35142367
reset ARP table at 2008 DSN Server and veried correct MAC address shows with IP.
Cannot ping router but can ping internal workstations at server. Ran DNS tests on properties screen and recursive test failed.
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by:Scovndrel
ID: 35142451
If you can't ping the router, you won't be able to do external DNS name resolution. The DNS will clear itself up once the router thing is resolved.

So let me paraphrase:

You swapped out the router, cleared the ARP cache on the server, pinged the IP address, and it successfully ARPed and cached the result, but does not get ping replies?

If that's the case, I'd be looking at the configuration on the router. Does it have a firewall component? That brings up a good point, by the way. If you can't communicate with the router, how did you configure it to begin with?

Did Mediacom supply the new router? If so, I would be getting their support on the phone to find out what gives, and if they can't figure it out, I'd have them send out a new one.

I tend to go with whatever device the ISP supplies, because it generally works and problems like this become _their_ problem.
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Author Comment

by:pmcgovern
ID: 35142594
Router is Linksys WRVS4400N that I supplied. From a workstation on domain  I can connect to router and config. If I use 4.2.22 for DNS server I can browse internet. It is only from 2008 Server that I cannot ping router or resolve external addresses or IP's. From server I can ping internal workstations by ip or name. If I remove Forwarders and use Root Hint I still cannot ping router or external addresses. As soon as I plug old router back to switch all is OK. Seems something at 2008 DNS Server is still configured for old router. Shut firewall off. Thanks for you help.
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Scovndrel earned 500 total points
ID: 35142779
That's really weird that clearing the ARP cache didn't work then. That's the only thing I can think of that would have a problem with the swap. Sure, there are places where the 2008 server has references to the IP address, since the IP stays the same, the only thing that should notice when the underlying device changes is ARP.

After you cleared the ARP cache, did you look at the ARP table to verify that it was empty?

Are there any intelligent managed switches involved?

Is this a virtual server? Might have to clear the ARP cache on the host if that is the case. A simple power cycle should do the trick.

Just for testing purposes, what happens if you set the router to a different IP address? Interested to know if the server can ping it on a different IP. How many statically assigned devices do you have? I guess worst case, if it responds to a different IP, would be to change your default gateway. Shouldn't have to do that for a simple router device change, I know.
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Author Closing Comment

by:pmcgovern
ID: 35165737
The ARP cache was the problem. I did a "netsh interface ip delete arpcache" and problem cleared. Not sure why arp -d {ip} did not fix. THanks for you help.
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Expert Comment

by:Scovndrel
ID: 35167330
It's not the first command I have found that doesn't work like I expect on Windows 2008, but usually there's some sort of error. I just tried it on a Windows 2008 (not R2) server and it worked OK. The ARP entry disappeared from the list when I ran the command. Very strange. Glad you got where you needed to be though, and I appreciate te alternate method of clearing the ARP cache. I'll tuck that away for later.

Thanks for the points!
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