VirtualBox: two network interfaces (NAT and host-only ones) in a Debian guest on Ubuntu

Question

I created a Debian VM on VirtualBox with two interfaces: a NAT one (for accessing internet) and a host-only one. However, I do not know how to make both interfaces work at the same time. If I the define the host-only as the adapter 1, I can access my VM from the host but not the internet; if I define the NAT one as adapter 1, I can access the internet but cannot reach my guest Debian.

So, how could I make both interfaces work together?

Note: I am still trying to map some port from my host to the SSH port from my guest SO, so there is no need to suggest me to do it :)

EDIT: This is the output of ifconfig when the first adapter is the host-only one:

eth0      Link encap:Ethernet  HWaddr 08:00:27:f6:b2:45  
          inet addr:192.168.56.101  Bcast:192.168.56.255  Mask:255.255.255.0
          inet6 addr: fe80::a00:27ff:fef6:b245/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:495 errors:0 dropped:0 overruns:0 frame:0
          TX packets:206 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:48187 (47.0 KiB)  TX bytes:38222 (37.3 KiB)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:8 errors:0 dropped:0 overruns:0 frame:0
          TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:560 (560.0 B)  TX bytes:560 (560.0 B)

This is the output of netstat -nr when the first adapter is the host-only one:

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.56.0    0.0.0.0         255.255.255.0   U         0 0          0 eth0

This is the output of ifconfig when the first adapter is the NAT one:

eth0      Link encap:Ethernet  HWaddr 08:00:27:f6:b2:45  
          inet addr:10.0.2.15  Bcast:10.0.2.255  Mask:255.255.255.0
          inet6 addr: fe80::a00:27ff:fef6:b245/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:53 errors:0 dropped:0 overruns:0 frame:0
          TX packets:59 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:6076 (5.9 KiB)  TX bytes:5526 (5.3 KiB)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:16 errors:0 dropped:0 overruns:0 frame:0
          TX packets:16 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:1664 (1.6 KiB)  TX bytes:1664 (1.6 KiB)

This is the output of netstat -nr when the first adapter is the NAT one:

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
10.0.2.0        0.0.0.0         255.255.255.0   U         0 0          0 eth0
0.0.0.0         10.0.2.2        0.0.0.0         UG        0 0          0 eth0

Solution 1

The solution was pretty simple: I just had to add the following lines into the Debian virtual machine's /etc/network/interfaces file:

allow-hotplug eth1
iface eth1 inet dhcp

The second line instructs the interface to obtain an IP via DHCP. The first line loads the interface at boot time.

To apply the changes to a running system, invoke:

ifup eth1

The name for the eth1 interface may vary, use ifconfig -a to list all available interfaces.

EDIT: full /etc/network/interfaces:

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
allow-hotplug eth0
iface eth0 inet dhcp

allow-hotplug eth1
iface eth1 inet dhcp

Solution 2

I was facing similar problem with my Ubuntu 14.04 VM, and Solution suggested by @brandizzi for Debian worked with little change.

EDIT: file /etc/network/interfaces:


# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet dhcp

auto eth1
iface eth1 inet dhcp

For UBUNTU 16.04

Run command

ifconfig -a

Look for new interface like in my case it is 'enp0s8'

EDIT file /etc/network/interfaces:

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto enp0s3
iface enp0s3 inet dhcp

auto enp0s8
iface enp0s8 inet dhcp  

Solution 3

In Ubuntu 18.04 host, VirtualBox 6.1, using Ubuntu 19.04 as guest

In the guest edit /etc/netplan/50-cloud-init.yaml file, add two lines as shown below (before the version line). Looks like the network configuration in the guest is set up only to handle one network and the second one has to be added manually

network:
    ethernets:
        enp0s3:
            dhcp4: true
        enp0s8:
           dhcp4: true
    version: 2

Solution 4

Both adapter should be configured in Debian

It seems that in both case you only have one adapter configured, hence your problem.

Create 2 adapters in the VirtualBox configuration of your VM and then start it. If you see only one configured adapter when using ifconfig (a single eth0, no eth1 too), then you should use the network configuration tool for Debian (Network Manager, ifupdown, etc.) to configure both interface in DHCP. So you should have eth0 and eth1 in DHCP.

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Comments

[brandizzi]

Well, they are separated (my NAT space is 10.0.2.0/24 and my NAT is 192.168.56.0/24).

[George M]

Can you edit your question to include the output of ifconfig and netstat -nr so we can see how the interfaces and routing are configured?

[brandizzi]

Ok, I added the output of the commands to the question.

[davolfman]

I can confirm. Debian doesn't setup the second interface in /etc/network/interfaces. Fixed my problem, thanks. For potential debugging, this is two virtio interfaces provided by Virtualbox. One is the NAT interface used for internet access (NATs are provided individually by vbox), the other is a host-only network with DHCP in a completely different private IP class. Debian version tested 6.0.6 x64.

[John Nicholas]

can you please post your whole /etc/network/interfaces please. Have been struggling with this for 2 days now.

[brandizzi]

@JohnNicholas done. Note that you should edit the guest /etc/network/interfaces file.

[John Nicholas]

cheers, mine was the same. My problem was that when i had the NAT adapter first in vbox the other (host) adapter would try to use the dhcp server on that adapter and all would go wrong. When I ordered the adapters in vbox as host only then NAT all started to work (irrespective of their ordering in linux interestingly enough). Netctl didn't have this problem in another vm.

[Elliot Su]

Under centOs there is no directory /etc/network. Still I would like to have both the NAT networking and host-only working. When I do ifconfig, I can only see one interface. Any ideas what I need to do on CentOs?

[brandizzi]

@user152468 I know nothing about CentOS. You might prefer to ask a new question on how to do it on CentOS.

[Maksim Luzik]

This also now applies to Debian 9+ (Ubuntu 16 setup)

[yahermann]

This works great, thanks! However Ubuntu 18 now uses a new interface called "netplan". Any idea how to replicate the above in netplan?

[Seb T]

In Ubuntu 19.10 the file is called /etc/netplan/01-netcfg.yaml. After the change execute sudo netplan apply to make the changes effective.

[camillo777]

This worked as well for Debian 10 on a OSX host VirtualBox 6.1.12

[Hzzkygcs]

Thank you! You might want to make your words clearer. The name for the eth1 interface may vary. Use ifconfig -a to find the interface name. I myself added the interface name that existed in ifconfig -a, but didn't exist in ifconfig.