Obrigado a todos que responderam!
O seguinte tutorial em alemão finalmente trouxe a solução (a parte da rede). Meu Host-IP e IP adicional não estavam na mesma sub-rede: link
0. Informações da minha empresa de hospedagem sobre o endereço IP adicional e o endereço Mac
Host-IP: _hostIP_
Additional IP: _additionalIP_
Gateway: _gatewayIP_
Maske: 255.255.255.248
Your IP _additionalIP_ has the following separate MAC-adress for virtualisation purposes:
Mac-address for the nic: _macaddress_
1. No host
iptables -P FORWARD ACCEPT
sysctl -w net.ipv4.ip_forward=1
# Add the Gateway as an IP-address on the host, in the following way (not the actual additional IP):
ip addr add _gatewayIP_/255.255.255.248 dev eth0
# Add a route for the 2nd additional ip in the following way
route add -host _additionalIP_ gw _additionalIP_
# make the changes persistent - this part is not tested!
emacs /etc/network/interfaces
# ----------------------------------------
# Loopback device:
auto lo
iface lo inet loopback
# device: eth0
auto eth0
iface eth0 inet static
address _hostIP_
broadcast _broadcast_
netmask 255.255.255.224
gateway _gateway_
post-up mii-tool -F 100baseTx-FD eth0
# default route to access subnet
up route add -net 46.4.xx.xx netmask 255.255.255.224 gw 46.4.xx.xx eth0
up ip addr add _gatewayIP_/255.255.255.248 dev eth0
up route add -host _additionalIP_ gw _additionalIP_
# ----------------------------------------
2. No host: altere as configurações de convidado
# set the mac-address of the guests nic to the virtual mac-address we got for our additional ip
# bridgeadapter1 is the network card from the Host that should be used for the bridge
VBoxManage modifyvm VMGuest --nic1 bridged --bridgeadapter1 eth0 --nictype1 Am79C973 --macaddress1 _macaddress_
VBoxHeadless -startvm VMGuest
3. No convidado
# connect via internal network and edit the network-configuration
emacs /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
auto eth0
iface eth0 inet static
address _additionalIP_
netmask 255.255.255.248
gateway _gatewayIP_
allow-hotplug eth1
auto eth1
iface eth1 inet dhcp
# --------------------------------------------------
shutdown -r now