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Problems with Network - possible loop or duplicate IP on network

Posted on 2013-05-31
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Last Modified: 2013-08-13
I have a new Buffalo NAS server with a static IP.  If I plug my laptop directly into the NAS or if I plug the nas and a laptop into a isolated switch I can get a constant ping with no problems.

If I plug the nas and my laptop into any one of 3 switches on our network, I get one Ping out of every 10 tries when I do a ping 10.x.x.27 -t

If I Plug the nas and my laptop into the isolated switch, it works fine again.  If I plug that switch into anyone of the 3 switches on our network it immediately goes back to 1 out of 10 pings are successful.

Trying to figure out how to diagnose this.

Any help would be greatly appreciated.
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Question by:BFanguy
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15 Comments
 
LVL 34

Expert Comment

by:Paul MacDonald
ID: 39211403
It appears the NAS is using the same static IP address already assigned to another device on the network.  

If you use DHCP or DNS on your network, it should be easy enough to figure out what the other device is and either change its address or give the NAS a new static IP.
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Expert Comment

by:dougone
ID: 39211672
the way to trouble shout is you know it works on an isolated switch..just plug the laptop in the non isolated switch and try to ping that address..if it ping back it is what the above person said..figure out an address that is not used and set it on the nas. if it doesn't ping back that wasn't your problem..try to ping another device on that network..if that doesn't work maybe the duplicate address is in the laptop? If it does ping back ok check to see if there is a setting in the router that does not respond to pings..some routers can be configured to not respond to pings..hope this helps.
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Author Comment

by:BFanguy
ID: 39211732
we are 99.99% positive that this address is not used anywhere and my laptop is on dhcp.

today I plugged just the nas into one of our network switches and it came up fine, no problems pinging from anywhere - we did not change anything since yesterday except we left it unplugged from the switch for 20 hours.

I then plugged a cable into the 2nd nic on the nas into a separate switch on a different subnet (to be used by the 2nd nics in our vmhost servers for iscsi) and it immediately started to flake out - pings started failing 4 out of 10, then 5 out of 10.... to 9 out of 10.

I unplug the 2nd nic on the nas and it still does not work.
power off the nas, unplug both nics, power back on, plug back in the first nic - pings 1 out of 10 times.
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LVL 34

Expert Comment

by:Paul MacDonald
ID: 39211745
So...both NICs on the NAS have the same IP address?  That would mess with the switches, and it might take the switches a few minutes to realize you'd unplugged one of the NICs.  That would explain the behavior you're seeing.

Can you verify the NIC configuration on the NAS, and - if both NICs have the same IP - can you change the IP for one NIC?  If not, you may need to set up some sort of Active/Passive role for the NICs.
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Author Comment

by:BFanguy
ID: 39211749
nas has nic 1 with 10.10.1.27, nic 2 10.30.1.27
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LVL 34

Expert Comment

by:Paul MacDonald
ID: 39211751
What's the subnet mask?
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Author Comment

by:BFanguy
ID: 39211755
255.255.255.0 for both
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LVL 34

Expert Comment

by:Paul MacDonald
ID: 39211763
Interesting.  What if you change one to .28 (or anything other than .27)?  Just one.
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Author Comment

by:BFanguy
ID: 39211766
tried .20  .21  .22  same problem..
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LVL 34

Expert Comment

by:Paul MacDonald
ID: 39211774
So you had one NIC with 10.10.1.27, and the other with 10.30.1.21 and it still locked up the network?  Please verify that for me.

You said above you had some success when only one NAS NIC was connected.  It may be there's a problem with the other NIC.  Can you try to verify that?  Just leave one NIC plugged in for 15 minutes or so, make sure it's working, unplug the one NIC wait 5 minutes, then plug in the second NIC and see if the problem shows up?
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Author Comment

by:BFanguy
ID: 39211805
yes.
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LVL 34

Expert Comment

by:Paul MacDonald
ID: 39211877
"yes." what?
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Author Comment

by:BFanguy
ID: 39211967
sorry, i had to get on a conference call..

So you had one NIC with 10.10.1.27, and the other with 10.30.1.21 and it still locked up the network? - yes

 Just leave one NIC plugged in for 15 minutes or so, make sure it's working - if i unplug the 2nd nic, it never goes back to normal (still only gets 1 of 10 sucessful pings)
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Accepted Solution

by:
BFanguy earned 0 total points
ID: 39394190
it was a problem with the NAS device itself creating a broadcast storm with igp protocol.
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Author Closing Comment

by:BFanguy
ID: 39404151
found the problem myself
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