Maximum Outgoing Connections?

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satvgirl
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Joined: 12. May 2014, 20:58

Maximum Outgoing Connections?

Post by satvgirl »

I have a Red Hat 6 host running several vm's. All of the guest vm's are CentOS 6. Recently we seem to be hitting some kind of outgoing connection limit. When this happens, you can still ssh into any of the vm's, but you can't do any outgoing connections such as an DNS lookup, connect to any webpage or ssh from the vm to another server from any of the vm's. While outgoing connections won't work from the vm's, the host machine is still able to make outgoing connections. All vm's are using NAT.

I have not been able to pinpoint at what number of connections this happens as the issue will present one minute and the next everything seems to work as expected. What I am hoping to find out is:

1) Has anybody else seen this issue? And if yes, what did you do to correct it.
2) Any suggestions on how to even go about troubleshooting this as we can't seem to figure out the number of connections that this breaks at.
noteirak
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Re: Maximum Outgoing Connections?

Post by noteirak »

Personally, and I do not have hard facts to back this up, I would expect some kind of limit. Each connection info would need to be stored by Virtualbox in some kind of mapping table.
I would expect Virtualbox to run out of space (or internal IDs) to store all these infos at some point. How many VMs do you have running at the same time?
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satvgirl
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Re: Maximum Outgoing Connections?

Post by satvgirl »

We have 5 VM's running concurrently.
noteirak
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Re: Maximum Outgoing Connections?

Post by noteirak »

Is there a reason you chose NAT and not Host-Only or Bridged in your case? NAT is not the best choice when it comes to have more than one or two VMs really.
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satvgirl
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Re: Maximum Outgoing Connections?

Post by satvgirl »

noteirak wrote:Is there a reason you chose NAT and not Host-Only or Bridged in your case? NAT is not the best choice when it comes to have more than one or two VMs really.
Our host is in a hosted environment and we cannot get IP addresses for each individual VM. With limited knowledge of networking and virtualbox, NAT and port forwarding seemed the easiest way to go.
Smackey's dad
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Re: Maximum Outgoing Connections?

Post by Smackey's dad »

Not sure how you are able to SSH into the VM which only has NAT as under NAT VMs cannot see each other and even the HOST cannot SSH into the VM.

I suspect if multiple VMs make simultaneous connections the Host will have to NAT that over as coming from different (host) ports so it can receive the responses correctly and send them back to the guests. I would troubleshoot by making sure only one VM is making active connections first and see how things go. I would them make two guests make simultaneous outgoing requests, etc. I would let the guests make requests on the same outgoing port first to maximize potential for conflict/issues.
satvgirl
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Re: Maximum Outgoing Connections?

Post by satvgirl »

Smackey's dad wrote:Not sure how you are able to SSH into the VM which only has NAT as under NAT VMs cannot see each other and even the HOST cannot SSH into the VM.
We are not ssh'ing from one VM to another. We can ssh to the VM using port forwarding. So, in effect, we are ssh'ng to the host machine which then port forwards the request to the VM. Works very well actually. Each VM is listening on a different port for the ssh connection as we are not using the default port.

Incidently, we realized that the host and VirtualBox had been running for more than two years without a reboot. We shutdown all VM's, rebooted the host and restarted VirtualBox and all the VM's. We were then able to make more than 1000 simultaneous outgoing connections in each of three separate sessions from the VM's. While we still have not been able to pinpoint the exact cause of the issue, I think that noteirak might be on to something with "mapping table" and running out of space or internal ID's. The reboot seems to have flushed whatever it was.
noteirak
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Re: Maximum Outgoing Connections?

Post by noteirak »

Glad you made it work! Good old reboot
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