Setting Up a Two-Subnet Network with DHCP and Router using VirtualBox

This guide outlines the steps to configure a two-subnet virtual network environment using VirtualBox. It includes setting up a DHCP server, assigning static IPs, and enabling routing between subnets.

Step 1: Configure DHCP Server (using isc-dhcp-server)

1. Install DHCP Server (on Ubuntu/Debian)

   sudo apt update
   sudo apt install isc-dhcp-server

2. Edit DHCP Configuration

   sudo nano /etc/dhcp/dhcpd.conf

   Add the following:

   subnet 192.168.1.0 netmask 255.255.255.0 {
     range 192.168.1.100 192.168.1.150;
     option routers 192.168.1.1;
     option subnet-mask 255.255.255.0;
     option domain-name-servers 8.8.8.8;
   }

3. Assign Static IP to DHCP Server (optional but recommended)

   sudo ifconfig eth0 192.168.1.10 netmask 255.255.255.0 up

4. Start the DHCP Server

   sudo systemctl restart isc-dhcp-server

✅ Tip: Ensure all VMs (except router) have different MAC addresses to receive unique DHCP IPs. In VirtualBox, go to VM Settings > Network > Advanced > Generate new MAC.

Step 2: Configure the Router (tinycore13-1)

This VM acts as a bridge between the two networks.

1. Assign IP to Interface 1 (Network 1)

   sudo ifconfig eth0 192.168.1.1 netmask 255.255.255.0 up

2. Assign IP to Interface 2 (Network 2)

   sudo ifconfig eth1 192.168.2.1 netmask 255.255.255.0 up

3. Enable IP Forwarding

   sudo sysctl -w net.ipv4.ip_forward=1

Step 3: Configure tinycore14-1 (Network 2 Host)

1. Assign IP manually

   sudo ifconfig eth0 192.168.2.2 netmask 255.255.255.0 up

2. Set Default Gateway to Router’s eth1

   sudo route add default gw 192.168.2.1

Step 4: Client Configuration (Network 1)

• Clients in Network 1 get IPs from the DHCP server.
• Default gateway is provided automatically via DHCP (192.168.1.1).

You don’t need to manually configure gateway or IP on these machines.

Step 5: Verifying the Setup

1. From a Network 1 client:

   ping 192.168.2.2

2. From Network 2:

   ping 192.168.1.100  # or any DHCP-assigned IP

Optional: Use Netplan for Static IPs (Ubuntu systems)

Instead of ifconfig, you can configure static IPs using Netplan.

Example config for /etc/netplan/01-netcfg.yaml:

network:
  version: 2
  ethernets:
    eth0:
      addresses: [192.168.2.2/24]
      gateway4: 192.168.2.1
      nameservers:
        addresses: [8.8.8.8, 8.8.4.4]

Then apply:

sudo netplan apply

Summary

• DHCP Server gives IPs to Network 1 clients and sets 192.168.1.1 as the default gateway.
• Router (tinycore13-1) connects both subnets and performs IP forwarding.
• tinycore14-1 is manually configured in Network 2.
• Once MAC addresses are unique and IPs are set, devices from both networks can communicate using ping.