MacOS – Connection to VirtualBox machine drops as soon as VPN is enabled

By default, the NAB adapter simply works for me, without Cisco AnyConnect running.

But DNS lookup failed when Cisco AnyConnect is running, this is due to a critical bug in Ubuntu 12.10+, "bug 1048783: network name lookups broken in NAT network adaptors". See more details at, https://bugs.launchpad.net/ubuntu/+source/virtualbox/+bug/1048783

To workaround this, you would need to run the following cmd to use the host DNS lookup,

From an window command prompt (with VMNAME replaced with your VB name, e.g. "Ubuntu"),

cd "c:\Program Files\Oracle\VirtualBox"

VBoxManage modifyvm VMNAME --natdnshostresolver1 on

BTW, I have "NAT" by default for the 1st adapter, and a "Host-Only" for the 2nd adapter to get around the limitations with NAB only adapter. This setting works perfectly for me.

Make sure you reboot the virtualbox and save the state to preserve the previous settings, not only a power off.

So basically you have a host and a guest machine—both running Kubuntu 14.04—sharing a network connection that you want to connect to two different VPN’s, correct?

The issue I see is by default, VirtualBox is set to internally—within it’s own software networking code—NAT any guest connection based on the host connection’s network settings. Meaning for all intents and purposes, both your guest as well as host will be on the same network address sharing the same connection; with the guest really being subordinate to the host as far as the main connection goes.

I believe the best bet is to set the network connection on the guest install of Kubuntu 14.04 to a bridged networking connection as described here; emphasis mine:

When a guest is using such a new software interface, it looks to the host system as though the guest were physically connected to the interface using a network cable: the host can send data to the guest through that interface and receive data from it. This means that you can set up routing or bridging between the guest and the rest of your network.

And explained even more clearly here; again emphasis is mine:

Under the Bridged Adapter, your virtual machines behave as any other computer on the network where the hosting system resides; it bridges the virtual and physical networks. The outside world can directly communicate with the guest machine.

That is the key. You want your guest connection to have an independent network connection outside of the host machine’s VPN so it can connect to it’s own VPN or anything else outside of the host machine’s VPN.

Meaning, with NAT your network addresses for host and guest would be something like this when connected to your router as far as the outside world is concerned; using the subnet 123.456.789.x as an example:

• Kubuntu 14.04 Host: 123.456.789.0
• Kubuntu 14.04 Guest: 123.456.789.0

But with bridged mode set for the guest, your guest machine can grab a unique IP address from the router so the IP addresses could look like this with the guest in bridged mode:

• Kubuntu 14.04 Host: 123.456.789.0
• Kubuntu 14.04 Guest: 123.456.789.1

And that division between IP addresses is what I believe is the the key to allowing you to setup two independent and unique VPN connections on your setup.