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Ping intermittently times out with virtual machines

Posted on 2010-11-20
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Last Modified: 2012-05-10
I have 2 vmware guest images (redhat, centos) running on a windows 7 host. Both guests are set up for bridged. I initially noticed intermitted issues with the network where sometimes http requests would fail when issued from the hosts browser to the guest OSs apache. Then I did some tests with ping and in a batch of four ping requests, on average 2 would succeed and 2 would time out.

I'm wondering what the most likely source of these issues is. The bridged networking is conncted through my cable modem. Do the ping requests from the host to the guest go through the cable company's network even though both OSs reside on the same physical machine?

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Question by:opike
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Author Comment

by:opike
ID: 34179860
When I ping the guest OS's from a different physical machine than the host, I get a 100% response success rate.
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by:theras2000
theras2000 earned 250 total points
ID: 34179923
That's an interesting question.  I don't know, but it certainly seems the right path to take to finding why it's timing out.  What if you tracert from guest to host, does it show a hop to the router?

I'm guessing not, because the router would not bother trying to route, as it sees the traffic as being in the same subnet.  The switch side of the router would want to forward your traffic out any other LAN ports, but not out the same port that it came from (as it assumes that the target device already heard it if it lives on that network segment).  So this would mean that the VMWare bridging software has to intelligently pass the traffic directly to the guest.  This is my purely theoretical conclusion, and it would point to a fault on your local host or VMware software.

This older post suggests the problem is in a bad NIC, and the person was using his WLAN NIC, rather than a LAN NIC.  http://www.experts-exchange.com/Software/VMWare/Q_25444767.html
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Author Comment

by:opike
ID: 34193378
Thanks for your input. I also just set up spiceworks to help track this issue over time.
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by:
vmstat earned 250 total points
ID: 34243837
The packets from one guest to the next should not go out on the wire.  

I would run tcpdump on each guest and windump on the server check out vmnet-sniffer (if this exists on windows) to see if it will tell you anything else about what is going on.  Are the packets making it to the guests?  Could there be ARP issues?  What interface is the bridged interface?  What params is vmnet-bridge running with?
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Author Comment

by:opike
ID: 34386049
Switch from spiceworks to pandorafms for monitoring since it seems to be more compatible with linux OSes.
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