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Server losing connectivity.

Posted on 2011-05-06
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Last Modified: 2012-05-11
I have two servers on my job network that keep losing connection lately.  My network has a couple of different VLANS and when the servers disconnect they can't be reached by computers or users in other VLANS; but they can be reached by computers on the same VLAN.  If I'm on a computer with a different VLAN I will not be able to ping the server by name or IP address.  I'm also not able to remote desktop into it from a computer on a different VLAN.  This seems to happen at random times.  The common thread is the both servers have two NIC cards in different networks.  One NIC in our network and the other NIC in a vendor related networks.  In order to fix the problem I run this command from the command line of the problem servers    ipconfig /registerdns     Does anyone have a clue as to what might be the problem?
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Question by:dali6
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by:jrwarren
jrwarren earned 200 total points
ID: 35710848
Double check yoru DNS entries in AD.
  1)   A common problem can be a DNS server that responds with a negattive authoritative to the .local.
          Remove the DNS entry that is not asuthoritative

  2)  You may have a cached problem on a DNS server or a client that has assumed Master Browser.
         Run ipconfg /flushdns  and follow with ipconfig /rregisterdns on ALL DNS servers

  3)  Double check your switches/routers make sure they are not tryign to route vlan traffic to an invalid DNS server that would simulate problem 1 or 2.

Otherwise :
   Can you ping client to client when the servers go incommunicado?  ie, does a single NIC display this problem?
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by:sumandan
sumandan earned 200 total points
ID: 35714269
If you are unable to ping by ip address...it looks like a routing issue rather than a name/dns problem.
Since the server has two NIC cards sitting on two different vlans and two different gateways, I think the route cache is getting mixed up...I would think the "registerdns" is reloading the network service there by refreshing the route cache as well....what I would do is put persistant static routes on the server....like

route add -p <Vlan1 network> mask<netmask> gw<gateway ip to reach that vlan1>
route add -p <Vlan2 network> mask<netmask> gw<gateway ip to reach that vlan2>

That way, you are telling the server which NIC to use, to reach a certain Vlan
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Author Comment

by:dali6
ID: 35740601
jrwarren, thanks for responding.  I understand answers 2 and 3 but I don't understand answer 1.  It sounds very informative, can you explain that one a little more?
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Expert Comment

by:ChiefIT
ID: 35745011
DNS has NOTHING to do with resolving a ping by IP address and little to do with resolving by computername. You have a routing table problem. It's best, with two nics to set them up right so it's not a detrimental multihomed server.

Please provide an IPconfig /all of both servers and we will tell you to probably remove the default gateways on non-external nic.
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Author Comment

by:dali6
ID: 35755763
ChiefIT here is a snapshot of one of the servers with the IPconfig /all command output. ipconfig /all ipconfig /all
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Author Comment

by:dali6
ID: 35755783
Sorry, two of the same pictures showed up.
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by:ChiefIT
ID: 35762657
You have a multihomed machine. What's that about? One is on the 192.... subnet adn the other is on the 10... subnet. Multihoming a machine will cause problems with the routing table. It's suggested not to do this.

So, what are the two subnets about?
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by:ChiefIT
ID: 35762664
Since you have DNS servers on NIC 2 configured, I am assuming that's where your domain is at, (on the 10 space). For the time being, remove the default gateway off the nic that is 192.168..... Then, we will see what we can do about getting these up and going without multihoming the computers.
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Author Comment

by:dali6
ID: 35781617
Thanks ChiefIT;
    I removed the default gateway of the nic 192.168....  I'll keep an eye on it over the next two days.  The reason for the 2 nics and the 2 default gateways is get information from the sever to another LAN other than our own without using a router.  This all was working for close to a year without a problem.  Not sure why it chose now to start acting up.
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ChiefIT earned 1600 total points
ID: 35806541
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Author Closing Comment

by:dali6
ID: 35806576
Thanks all.  The problem hasen't popped up in over a week after I removed the default gateway from the 2nd NIC of both servers.  If the issue pops up again I'll do some more asking but so far things look good.  CheifIT, I will review that link.
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