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Hyper-V Question on Proper NIC Setup

Posted on 2014-08-31
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Comcast Business service is now saying my network is the issue.  Trying to get a handle on whether I am doing this all wrong, all right or somewhere in between.

We are hosting multiple VMs for different clients on a Dell server with 6 NICS, and another Dell server with 4 NICS.  We have one Cat5e going from the Comcast Modem to an unmanaged 24 port switch.  Multiple Cat5e spin out of the switch going separate routers which then plug into the NICS on the servers.

Network Portrayal
We have the NICs on the servers set to use DHCP from their respective router to get an address and then the VM that is attached to that NIC has a static set on it at the .2 address.

The top server has a network connection to our internal router so the Hosting machine can be managed internally  from our own network.  The bottom server is for running all of our own internal VMs which all participate in the same domained network.

Is this setup correct?  The basic issue we are seeing that we've blamed comcast for is that all routers will lose their connection at least once a day for about 3-4 minutes all at the same time.  We've plugged a laptop into the comcast modem and it experiences the same behaviour.  Comcast states that their box is running cleanly yet it appears that all connections drop and I'm staritng to wonder if a DNS issue doesn't exist that could be causing the issues.

Any thoughts would be greatly appreciated.
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Question by:dstewart83161
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by:Lionel MM
ID: 40296509
Logically it makes no sense to say that your network design works for hours on end and then for 3 to 4 minutes each day at the same time the design is flawed--so I agree with you that it highly likely a comcast modem issue. I too have a client on comcast in Lake Placid FL and they lose internet connectivity several times during the day--it only lasts a minute or two and so we have learned to deal with it because comcast refuses to take accountability for it. However if your internal network connections are also been dropped then it may be a DHCP issue where the time of life of each DHCP lease is renewed--however that should take seconds and not 3 to 4 minutes. It would be easy to see if it is an IP lease by giving all device static IP on a temp basis and see if the problem goes away. I can't think of any feasible DNS issue that could be causing this, not at the same time every day and for 3 to 4 minutes each time (highly unusual).
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Svet Paperov earned 2000 total points
ID: 40296556
It should be easy to determine where the problem is.
 
I presume that all Static IP addresses are part of the same public IP subnet and that you have connectivity between the networks via routing on that subnet. Meaning, even if you unplug the connection from the unmanaged switch to the Comcast modem, you should be able to access the hosts on network .15.x from network .16.x (if it’s allowed by Netgear firewalls) or at least, you should be able to ping Netgear 1’s static IP 1 from the console of Netgear 2.

Next time when the issue occurs, check again this connectivity: if it works it should be the modem in fault, if not it could be the unmanaged switch as well.

Since, you are experiencing the same issue when you plug a laptop directly to the modem, I would stick with your conclusion – just try to make your case with Comcast support.

Small note about the hosts: make sure the adapters used for the virtual networks are not shared with the management host : the “Allow management operating system…” checkbox must be cleared for all of them and you have to have a dedicated NIC on a dedicated IP subnet for management purposes.
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Expert Comment

by:vivigatt
ID: 40296607
If a laptop connected directly to the comcast device has the same issue, it is certainly a comcast issue.
If you can disconnect everything from the comcast device but the laptop and still have the same issue, then you are 100% certain that the issue is on comcast side and they should nor argue...
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Expert Comment

by:lrmoore
ID: 40297265
With multiple firewalls from different manufacturers all with interfaces sharing a common broadcast domain on the public side, you could have proxy arp issues caused by one or more of the firewalls. You woul have to disconnect everything except the laptop from the comcast device to verify that you fet the same behavior. Then add one firewall connection back at a time. This makes for a very long multi day process if it only occurs once or twice a day. Having said all that, it could very well be the comcast device. I dont trust them to be robust enough for any kind of enterprise setup.
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Author Comment

by:dstewart83161
ID: 40298589
lrmoore, could you explain the ARP issues a bit more.  I have had a slight doubt in my mind that one of the routers might be causing it as it does a "burst" or floods the network temporarily, almost like an accidental DOS attack.  Could an ARP issue cause this type of behaviour and if so, what could be done about it?
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by:Lionel MM
ID: 40298626
You said "
We've plugged a laptop into the comcast modem and it experiences the same behaviour. "

If that is the case then all the other devices were removed from the network, right? and if so then all the problem HAS TO BE Comcast's modem
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Author Comment

by:dstewart83161
ID: 40298649
We've not removed the other connects from the Comcast modem.  The laptop is there now as an additional check and to remove Comcast's first objection because they always want to know what it is doing with a direct connection.  The laptop is now doing about 10 different continuous pings to inside and outside addresses so we can understand more of what is happening when the issue happens.
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by:Lionel MM
ID: 40298693
We've not removed the other connects from the Comcast modem.
Do you have a Comcast modem or a Comcast router? What model is it?
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Author Comment

by:dstewart83161
ID: 40298791
it is their SMC model with a modem / router built in one.  It has 4 LAN ports and I currently allow it to hand out DHCP addresses on its own LAN of 10.1.10.x  All of the statics from the internal routers I have setup will bypass this LAN and the firewall which is built into it as well.
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Expert Comment

by:Lionel MM
ID: 40299370
Well you said it happens "all at the same time" does that mean the same time of day or all the routers lose connections together? If same time of day disconnect everything except laptop from modem. You may also want to install network monitoring software to find the problem. I use this and it helps find trouble spots on my network but others may have even better suggestions
www.paessler.com/prtg
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Author Comment

by:dstewart83161
ID: 40301348
all of the routers lose their connection at the same time as well as the laptop.  I did change the Allow Management Operating System to uncheck them all as Svet Paperov suggested.  So far there has not been a reoccurence but the week is young as they would say.
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Author Closing Comment

by:dstewart83161
ID: 40333868
Have implemented Svet suggestion to not Allow Management Operating System to share the NIC on Hyper-V and it appears that things have significantly settled down.  Thanks so much to everyone for the info and sanity check.
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