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Okay friends! I would really appreciate some help this time! =|

I'm using VirtualBox virtualizer and I'm trying to make my guest machines have access to the internet using ONLY a "host-only" network interface (VirtualBox).

According to the official documentation in https://www.virtualbox.org/manual/ch06.html using a "host-only" network interface I have the following "network modes" (accesses)...

VM  <-> Host     | YES
VM1 <-> VM2      | YES
VM   -> Internet | NO

However, there are A LOT of documentations on the internet that informing you can access the internet (using only the "host-only" interface) from a guest machine using the following "trick"/"workaround" (example) on the host machine...

sudo iptables -A FORWARD -o <HOST_INTERFACE_WITH_INTERNET> -i vboxnet0 -s 192.168.56.0/24 -m conntrack --ctstate NEW -j ACCEPT
sudo iptables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
sudo iptables -A POSTROUTING -t nat -j MASQUERADE
sudo sysctl -w net.ipv4.ip_forward=1

I tested many and many examples. The iptables.service is running correctly on my host machine. WHAT AM I DOING WRONG?

My host is a Linux Manjaro (Linux Arch based).

Thanks a lot!

Below are some sources with information about the "trick"/"workaround" I mentioned...

http://archlinux.org.ru/forum/topic/2219/ http://nerdbynature.de/s9y/2015/06/09/VirtualBox-switching-to-Host-only-networking https://askubuntu.com/questions/293816/in-virtualbox-how-do-i-set-up-host-only-virtual-machines-that-can-access-the-in https://cuckoo.sh/docs/installation/host/routing.html https://downloads.cuckoosandbox.org/docs/installation/guest/network.html https://github.com/cuckoosandbox/cuckoo/issues/1376 https://jackal777.wordpress.com/2012/02/13/internet-access-in-virtualbox-host-only-networking/ https://kyrofa.com/posts/virtualbox-internet-access-with-host-only-network https://precisionsec.com/virtualbox-host-only-network-cuckoo-sandbox-0-4-2/ Virtualbox NAT and host-only connection https://unix.stackexchange.com/questions/74663/virtualbox-nat-host-only-adapter https://www.howtogeek.com/howto/4922/week-in-geek-the-fixing-slow-internet-in-virtualbox-xp-guest-edition/ https://www.rffuste.com/tag/cuckoo/ https://www.virtualbox.org/manual/ch06.html

Below are some of the MANY examples I tested...

 > --------------------------------------------
sudo iptables -t nat -I POSTROUTING -s 192.168.56.0/24 -j MASQUERADE
sudo sysctl net.ipv4.ip_forward=1
sudo iptables -P FORWARD ACCEPT
sudo iptables -t nat -P POSTROUTING ACCEPT
 < --------------------------------------------
 > --------------------------------------------
sudo iptables -A FORWARD -i vboxnet0 -s 192.168.56.0/24 -m conntrack --ctstate NEW -j ACCEPT
sudo iptables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
sudo iptables -A POSTROUTING -t nat -j MASQUERADE
sudo sysctl -w net.ipv4.ip_forward=1
 < --------------------------------------------
 > --------------------------------------------
sudo iptables -A FORWARD -o <HOST_INTERFACE_WITH_INTERNET> -i vboxnet0 -s 192.168.56.0/24 -m conntrack --ctstate NEW -j ACCEPT
sudo iptables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
sudo iptables -A POSTROUTING -t nat -j MASQUERADE
sudo sysctl -w net.ipv4.ip_forward=1
 < --------------------------------------------
 > --------------------------------------------
sudo iptables -A FORWARD -o <HOST_INTERFACE_WITH_INTERNET> -i vboxnet0 -s 192.168.56.0/24 -m conntrack --ctstate NEW -j ACCEPT
sudo iptables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
sudo iptables -t nat -F POSTROUTING
sudo iptables -t nat -A POSTROUTING -o <HOST_INTERFACE_WITH_INTERNET> -j MASQUERADE
sudo sh -c "echo 1 > /proc/sys/net/ipv4/ip_forward"
 < --------------------------------------------
 > --------------------------------------------
sudo iptables -A FORWARD -o <HOST_INTERFACE_WITH_INTERNET> -i vboxnet0 -s 192.168.56.0/24 -m conntrack --ctstate NEW -j ACCEPT
sudo iptables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
sudo iptables -A POSTROUTING -t nat -j MASQUERADE
sudo sysctl -w net.ipv4.ip_forward=1
sudo sysctl -w net.ipv4.conf.all.proxy_arp=1
 < --------------------------------------------
 > --------------------------------------------
sudo sysctl -w net.ipv4.ip_forward=1
sudo iptables -F
sudo iptables -t nat -A POSTROUTING -o <HOST_INTERFACE_WITH_INTERNET> -j MASQUERADE
sudo iptables -A FORWARD -i <HOST_INTERFACE_WITH_INTERNET> -o vboxnet0 -j ACCEPT
sudo iptables -A FORWARD -i vboxnet0 -o <HOST_INTERFACE_WITH_INTERNET> -j ACCEPT
 < --------------------------------------------
 > --------------------------------------------
sudo iptables -A FORWARD -i vboxnet0 -s 192.168.56.0/24 -m conntrack --ctstate NEW -j ACCEPT
sudo iptables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
sudo iptables -A POSTROUTING -t nat -j MASQUERADE
sudo sysctl -w net.ipv4.ip_forward=1
 < --------------------------------------------
 > --------------------------------------------
sudo bash -c "printf \"net.ipv4.ip_forward = 1\nnet.ipv4.conf.all.proxy_arp = 1\n\" >> /etc/sysctl.conf"
sudo sysctl -p
sudo iptables -t filter -I FORWARD --in-interface vboxnet0 --out-interface <HOST_INTERFACE_WITH_INTERNET> --source 192.168.56.0/24 -j ACCEPT
sudo iptables -t filter -I FORWARD --in-interface <HOST_INTERFACE_WITH_INTERNET> --out-interface vboxnet0 --destination 192.168.56.0/24 -j ACCEPT
sudo iptables -t nat -I POSTROUTING -o <HOST_INTERFACE_WITH_INTERNET> -j MASQUERADE
 < --------------------------------------------
 > --------------------------------------------
sudo iptables -A POSTROUTING -o enp+ -t nat -j MASQUERADE
sudo iptables -A POSTROUTING -o wlp+ -t nat -j MASQUERADE
 < --------------------------------------------
 > --------------------------------------------
sudo iptables -A PREROUTING -t mangle -i vboxnet+ -j MARK --set-mark 1
sudo iptables -A POSTROUTING -o enp+ -t nat -m mark --mark 1 -j MASQUERADE
sudo iptables -A POSTROUTING -o wlp+ -t nat -m mark --mark 1 -j MASQUERADE
 < --------------------------------------------
 > --------------------------------------------
sudo iptables -t nat -A POSTROUTING -o <HOST_INTERFACE_WITH_INTERNET> -s 192.168.56.0/24 -j MASQUERADE
sudo iptables -P FORWARD DROP
sudo iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
sudo iptables -A FORWARD -s 192.168.56.0/24 -j ACCEPT
sudo iptables -A FORWARD -s 192.168.56.0/24 -d 192.168.56.0/24 -j ACCEPT
 < --------------------------------------------
 > --------------------------------------------
sudo sysctl -w net.ipv4.ip_forward=1
sudo iptables -A FORWARD -o <HOST_INTERFACE_WITH_INTERNET> -i vboxnet0 -s 192.168.56.0/24 -m conntrack --ctstate NEW -j ACCEPT
sudo iptables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
sudo iptables -t nat -A POSTROUTING -s 192.168.56.0/24 -o <HOST_INTERFACE_WITH_INTERNET> -j MASQUERADE
sudo iptables -I INPUT 1 -i vboxnet0 -j ACCEPT
 < --------------------------------------------
 > --------------------------------------------
echo 1 | sudo tee /proc/sys/net/ipv4/ip_forward
sudo sysctl -p /etc/sysctl.conf
sudo iptables -I FORWARD -i vboxnet0 -d 192.168.56.0/255.255.255.0 -j DROP
sudo iptables -A FORWARD -i vboxnet0 -s 192.168.56.0/255.255.255.0 -j ACCEPT
sudo iptables -A FORWARD -i <HOST_INTERFACE_WITH_INTERNET> -d 192.168.56.0/255.255.255.0 -j ACCEPT
sudo iptables -t nat -A POSTROUTING -o <HOST_INTERFACE_WITH_INTERNET> -j MASQUERADE
 < --------------------------------------------
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2
  • 1
    askubuntu.com/questions/293816/… has the clue - 2 Network Interfaces. 1 Host-Only, and 1 NAT. NAT allows you internet access, and the Host-Only... well do what you want with it. Or you mean to have a purely host-only networking and still have internet access?
    – Darius
    Aug 4, 2017 at 6:38
  • @Darius "Or you mean to have a purely host-only networking and still have internet access?" -> Yes! Exactly! Thanks!
    – Eduardo Lucio
    Aug 4, 2017 at 13:40

1 Answer 1

Reset to default
4

INTRODUCTION

It is a complete guide to have the accesses "VM <-> Host", "VM1 <-> VM2" and "VM -> Internet" on the guests using a single network interface ("host-only") on VirtualBox.

IMPORTANT: Run all the commands as "root".

EXECUTE ON HOST

NOTE: We use a Manjaro (Arch based) host as a template. You may need adjustments and changes to other distros.

You need to copy the iptables template configuration file...

$ cp /etc/iptables/empty.rules /etc/iptables/iptables.rules

... so you can start the "iptables.service".

Enable and start "iptables.service"...

$ systemctl enable --now iptables.service

Enable IP forwarding...

$ sysctl -w net.ipv4.ip_forward=1
$ printf "net.ipv4.ip_forward=1\n" >> /etc/sysctl.d/30-ipforward.conf

Add the following iptables rules. This will forward packets through the host ("vboxnet0") and to the internet...

TEMPLATE I 
$ iptables -t filter -I FORWARD --in-interface vboxnet0 --out-interface <HOST_INTERFACE_WITH_INTERNET> --source 192.168.56.0/24 -j ACCEPT
$ iptables -t filter -I FORWARD --in-interface <HOST_INTERFACE_WITH_INTERNET> --out-interface vboxnet0 --destination 192.168.56.0/24 -j ACCEPT
$ iptables -t nat -I POSTROUTING -o <HOST_INTERFACE_WITH_INTERNET> -j MASQUERADE

... OR add the following iptables rules...

TEMPLATE II 
$ iptables -t nat -I POSTROUTING -s 192.168.56.0/24 -j MASQUERADE
$ iptables -P FORWARD ACCEPT
$ iptables -t nat -P POSTROUTING ACCEPT

NOTE: On the "TEMPLATE II" you do not need to inform the name of the host interface (<HOST_INTERFACE_WITH_INTERNET>) and the name of the VirtualBox interface (vboxnet0). In that way any host interface that has internet will work, that is, I do not have to adjust the name of the interface that has internet whenever it changes. An example of this is when we change from the wired interface (eg .: enp4s0f2) to the wireless interface (eg: wlp3s0) and vice-versa.

FURTHER QUESTION: I presented two ways to configure "iptables" because I do not know if there is any advantage in using the "TEMPLATE I". Any comment?

TIP: To find out the name of the network interface (<HOST_INTERFACE_WITH_INTERNET>) that has internet use the "ip a" command.

Save rules to iptables configuration and restart the service...

$ iptables-save > /etc/iptables/iptables.rules
$ systemctl restart iptables.service

Enable and start "dnsmasq" in host...

$ systemctl enable --now dnsmasq.service

NOTE: "dnsmasq" is a small caching DNS proxy and DHCP/TFTP server.

EXECUTE ON GUEST

NOTE: We use a CentOS 7 guest as a template. You may need adjustments and changes to other distros.

Configure the network interface according to the model...

NOTE: The network configuration file is in the "/etc/sysconfig/network-scripts/" folder path.

BOOTPROTO=static
DEVICE=<NETWORK_INTERFACE_NAME>
DNS1=<HOST-ONLY_HOST_IP>
GATEWAY=<HOST-ONLY_HOST_IP>
IPADDR=<HOST-ONLY_GUEST_IP>
IPV6INIT=NO
NETMASK=255.255.255.0
NM_CONTROLLED=yes
ONBOOT=yes
TYPE=Ethernet
USERCTL=NO
ZONE=

Eg.:

BOOTPROTO=static
DEVICE=eno16777736
DNS1=192.168.56.1
GATEWAY=192.168.56.1
IPADDR=192.168.56.101
IPV6INIT=NO
NETMASK=255.255.255.0
NM_CONTROLLED=yes
ONBOOT=yes
TYPE=Ethernet
USERCTL=NO
ZONE=

Restart the network service...

$ systemctl restart network.service

To test...

$ curl http://www.google.com

REFERENCE

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