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VirtualBox networking for beginners

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When using VirtualBox for my OpenStack development I always configure two network adapters for ease of development. The first is a NAT adapter that enables the guest VM connectivity to the Internet via the host. The second network adapter is a host-only Adapter that enables my host computer (aka my terminal windows) to SSH directly to the guest VM, or to access a web interface for example. This enables the use of tools like ssh, scp, rsync etc easily with multiple VMs without thinking of different ports.

Having the two adapters is very convenient, however when you install products such as devstack or RDO these require additional steps to manage the interface and configure the installation. These steps are relatively straightforward but they make the most simple instructions more complex.

There are alternatives to using the NAT only adapter and enable port forwarding. For example you can configure port forwarding of port 2222 to the guest 22 with (when VM is not running):

$ VBoxManage modifyvm "vm-name" --natpf1 "guestssh,tcp,,2222,,22"
$ VBoxManage startvm "vm-name"

You can now connect to the guest VM via port forwarding on your host, in this case connecting to port 2222.

$ ssh user@localhost -p 2222

Personally I find this a disadvantage. You need to provide port forwarding for all ports you want to communicate on e.g. ssh (22), http (80) and keystone (5000). You need to do it in advance of using your VM, and you also need to do this for each VM.

However, depending on your needs and experience this is a valid alternative.

Ubuntu two adapter configuration

On Ubuntu, the following configuration file defines two DHCP network adapters.

$ cat /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

You can verify adapter information (e.g. IP address) using ifconfig.

$ ifconfig
eth0      Link encap:Ethernet  HWaddr 08:00:27:7f:a0:e2  
          inet addr:10.0.2.15  Bcast:10.0.2.255  Mask:255.255.255.0
          inet6 addr: fe80::a00:27ff:fe7f:a0e2/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:585 errors:0 dropped:0 overruns:0 frame:0
          TX packets:455 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:129820 (129.8 KB)  TX bytes:64215 (64.2 KB)

eth1      Link encap:Ethernet  HWaddr 08:00:27:66:8d:cb  
          inet addr:192.168.56.102  Bcast:192.168.56.255  Mask:255.255.255.0
          inet6 addr: fe80::a00:27ff:fe66:8dcb/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:221 errors:0 dropped:0 overruns:0 frame:0
          TX packets:152 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:28289 (28.2 KB)  TX bytes:19443 (19.4 KB)

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:65536  Metric:1
          RX packets:371 errors:0 dropped:0 overruns:0 frame:0
          TX packets:371 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:90509 (90.5 KB)  TX bytes:90509 (90.5 KB)

The ip command is also available.

To configure an IP with a fixed address on the host-only adapter network which is useful for many machines, you would use:

auto eth1
iface eth1 inet static
address 192.168.56.50
netmask 255.255.255.0
gateway 192.168.56.1

CentOS two adapter configuration

CentOS keeps a configuration file per interface. We start be determining the interface names.

$ ls -l /etc/sysconfig/network-scripts/ifcfg-*
-rw-r--r--. 1 root root 310 Mar 30 16:53 /etc/sysconfig/network-scripts/ifcfg-enp0s3
-rw-r--r--. 1 root root 278 Mar 30 17:00 /etc/sysconfig/network-scripts/ifcfg-enp0s8
-rw-r--r--. 1 root root 277 Mar 30 16:53 /etc/sysconfig/network-scripts/ifcfg-enp0s8e
-rw-r--r--. 1 root root 254 Sep 16  2015 /etc/sysconfig/network-scripts/ifcfg-lo

And then can review the per interface configuration with:

$ cat /etc/sysconfig/network-scripts/ifcfg-enp0s3
TYPE="Ethernet"
BOOTPROTO="dhcp"
DEFROUTE="yes"
PEERDNS="yes"
PEERROUTES="yes"
IPV4_FAILURE_FATAL="no"
IPV6INIT="yes"
IPV6_AUTOCONF="yes"
IPV6_DEFROUTE="yes"
IPV6_PEERDNS="yes"
IPV6_PEERROUTES="yes"
IPV6_FAILURE_FATAL="no"
NAME="enp0s3"
UUID="2c0bdd66-badc-449c-8db8-b2c85a716dab"
DEVICE="enp0s3"
ONBOOT="yes"

$ cat /etc/sysconfig/network-scripts/ifcfg-enp0s8
TYPE=Ethernet
BOOTPROTO=dhcp
DEFROUTE=yes
PEERDNS=yes
PEERROUTES=yes
IPV4_FAILURE_FATAL=no
IPV6INIT=yes
IPV6_AUTOCONF=yes
IPV6_DEFROUTE=yes
IPV6_PEERDNS=yes
IPV6_PEERROUTES=yes
IPV6_FAILURE_FATAL=no
NAME=enp0s8
UUID=4127685d-a7b9-4b8d-a399-6dcacdb3396d
DEVICE=enp0s8
ONBOOT=yes

You can verify the network configuration using the ip command.

$ ip addr
1: lo:  mtu 65536 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp0s3:  mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 08:00:27:32:c0:4c brd ff:ff:ff:ff:ff:ff
    inet 10.0.2.15/24 brd 10.0.2.255 scope global dynamic enp0s3
       valid_lft 15876sec preferred_lft 15876sec
    inet6 fe80::a00:27ff:fe32:c04c/64 scope link 
       valid_lft forever preferred_lft forever
3: enp0s8:  mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 08:00:27:43:22:85 brd ff:ff:ff:ff:ff:ff
    inet 192.168.56.103/24 brd 192.168.56.255 scope global dynamic enp0s8
       valid_lft 1056sec preferred_lft 1056sec
    inet6 fe80::a00:27ff:fe43:2285/64 scope link 
       valid_lft forever preferred_lft forever

CentOS does not provide ifconfig by default, it’s included in the net-tools package (RDO for example installs this).

$ sudo yum install -y net-tools
$ ifconfig
enp0s3: flags=4163  mtu 1500
        inet 10.0.2.15  netmask 255.255.255.0  broadcast 10.0.2.255
        inet6 fe80::a00:27ff:fe32:c04c  prefixlen 64  scopeid 0x20
        ether 08:00:27:32:c0:4c  txqueuelen 1000  (Ethernet)
        RX packets 437445  bytes 441847285 (421.3 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 142720  bytes 8897712 (8.4 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

enp0s8: flags=4163  mtu 1500
        inet 192.168.56.103  netmask 255.255.255.0  broadcast 192.168.56.255
        inet6 fe80::a00:27ff:fe43:2285  prefixlen 64  scopeid 0x20
        ether 08:00:27:43:22:85  txqueuelen 1000  (Ethernet)
        RX packets 14250  bytes 1708162 (1.6 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 15367  bytes 13061787 (12.4 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10
        loop  txqueuelen 0  (Local Loopback)
        RX packets 5706360  bytes 778262566 (742.2 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 5706360  bytes 778262566 (742.2 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

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