[SOLVED] How to inter-connect Oracle Virtualbox Virtual Machine Guest Computers

Many times there is the need to create a list of virtual servers with a goal of interconnecting each guest VM to other peer VMs on the same Virtualbox instance.

Background: I was in the process of installing 3 virtual servers on an Ubuntu Linux system viz: Hyperion Oracle Database(OLTP) server, Essbase OLAP server and an Oracle Enterprise Performance Management (EPM) server as middleware.
There is the technical requirement to interconnect these Windows Server OS servers in an enterprise environment using the "all-powerful" Virtualbox virtualisation tool.

Fig.1 Virtual Guests Servers on VirtualBox instance needing inter-connectivity.


Solution: 
1. Configure the network adapter of the guest VMs to be attached to an "Internal Network" on the network section of "Adapter 1".

Fig.2 Network adapter settings

2. Set up Virtualbox's DHCP server and add a connectivity IP range for the use of guest virtual machines. This configuration simulates a virtual router environment.

 This is done by running the command below which pegs the lower IP assignable to 10.13.13.101 and the upper to 10.13.13.254.
It also assigns the virtual "DHCP server" the IP 10.13.13.100 as scripted below for your use.



VBoxManage dhcpserver add --netname intnet                      
--ip 10.13.13.100 --netmask 255.255.255.0                       
--lowerip 10.13.13.101 --upperip 10.13.13.254 --enable          

Fig.3 command run to set up dhcpserver and accompanying settings



3.Put the firewall of the guest VM Operating Systems off totally.

Fig.4 Firewall settings



4. Switch on the VM guests.
    i) verify the IP assigned to each guest VM and
    ii) try interconnecting to each of the VMs from each other,
    for example: have  guest 1 ping guest 2 and vice versa.

Fig.5    A cross ping amongst guest Windows OS 1(10.13.13.101) and 2(10.13.13.102) are successful hence eureka!