I am using VirtualBox 5.1.8 (and 5.1.18) on Windows 7 with guest Kubuntu 16.04

Set up:

  • Guest has only one network interface with mode = NAT
  • Windows Firewall is Off (all profiles, all interfaces)
  • I have Bromium and Pulse secure installed on host (Windows)


  • I can ping any IP address on guest. ICMP packets go from VM to Host and onto the network and then back. I tested it using tcpdump on Linux (guest) and Wireshark on Windows (host).
  • I cannot connect to any IP address beyond VM:
    • Whenever I try to connect to any IP address outside VM I get "network unreachable" error
    • tcpdump on guest system shows that default gateway responds with ICMP message "network unreachable" to TCP connection request message.
    • Wireshark on host doesn't show any activity related to connection attempt.
  • Connecting to the same hosts from host (Windows) box works perfectly fine.
  • Bridging instead of NAT-ing works fine for the same guest system (when I set interface mode to Bridged connections work fine.).
  • Installed FreeBSD as guest on the same host and got the same problem (can ping, cannot connect)
  • One of my colleagues has exactly the same set up and it works fine for him.

My goal is to make NAT mode working again.

Tried so far:

  • I tried upgrading VirtualBox to version 5.1.18 -- didn't help
  • Downgrading VirtualBox to version 5.1.8 (last known working version)
  • Rebooting after each re-install and re-configuration of VM
  • Installing fresh VM and installing different OS (FreeBSD)
  • Using "Nat Network" mode

So my questions are:

  • What is causing NAT to drop TCP connections as inaccessible?
  • How can I track down what is dropping TCP connections?
  • How I can get NAT working again?

I cannot use bridged mode because I cannot have additional IP address on the network (besides the one I have for my Windows box). So I have to use NAT (or NAT Network)

  • I am not familiar with Bromium and Pulse secure, but have you tried removing or disabling them? You specifically mentioned them so I am assuming you have some suspicion they are involved in the problem.
    – acejavelin
    Mar 22, 2017 at 1:08
  • well, note that if NAT is on and working, you would not be able to ping the guest of connect to its services via TCP/UDP, from the Host unless you have configured port forwarding rules. Mar 22, 2017 at 2:55

1 Answer 1


I had my Windows (host) re-installed and it fixed the issue. Same setup.

  1. Reinstall Windows
  2. Install VirutalBox
  3. Add VM to the VirtualBox and start

It works as it used to.

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