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2008r2 networking grief

Posted on 2011-10-18
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Last Modified: 2015-01-09
Hello everyone,

Recently I had an issue with a switch loop, even though it was very brief it caused problems for a few servers that started to report duplicate IP addresses without reason.
This was sorted with the "netsh int ip reset" command, well on all but one.

The server I am still struggling with does not report any thing out of the ordinary in its event log but when it communicated with some host outside its own subnet it starts dropping packets in roughly 3 seconds intervals.

So to be brief I have tried to change its IP (it works), same IP on a different server (works), change drivers from Broadcom to inbuilt MS drivers (no change).
Ping from the server to another on the same subnet (works), ping from another server to the server on the same subnet (works).
Ping from another network (packet loss), ping to an external network (packet loss).
And since this issue cam at the same time a the duplicate IP address problems on the other servers we have tried to run "netsh int ip reset" on this one too (no change) and "arpretrycount = 0" as well (no change).
There is also no difference if the server gets its IP statically or dynamically.
And changing the servers IP address (which works) is unfortunately not an option as its in production with a database used by several remote hosts.


Any fresh ideas is much appreciated.
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Question by:hakonsv
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by:Paul MacDonald
ID: 36985834
What happens if you use a different port in the switch?
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by:hakonsv
ID: 36985903
Sorry, I forgot to mention that I have tried to move the server to a different switch entirely and the problem persisted.
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by:pwindell
ID: 36987882
Replace the Nic in the macine.  If it is onboard then disable it and add a Nic.  If that doesn't do anything you can just take the nic back out and go back to the original.  Just remember to set the original Nic to use DHCP before you remove or disable it,...if you don't then yo may get duplicate address notifications when you try to give the new nic the same IP the old one had.
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hakonsv earned 0 total points
ID: 36990647
Actually the problem was another server. I configured a span port on the switch and did a Wireshark capture. The pattern was that the other server firs produced a broadcast ARP to ask for the domain controller IP. Right after that there was a long sequence of ARPs from the other server towards the problem server on the format:

(X=the ip of the problem server, y1..yn is random other servers on the network)

who has ip X -> Tell y1..yn. This packets had the source mac of the "other server" and destination mac of the problem server.

The pattern was always appearing just before the problem was seen for the problem server. The solution was just a restart on the other server. Now everything is running smooth. Can someone explain to me what behaviour this is? Something in Windows that get mixed up after a netwoork L2 loop?

We saw the problem only on Windows 2008R2 servers, not Windows 2003.

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by:Paul MacDonald
ID: 36992551
Very interesting - thanks for posting the resolution.
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