Setting up a KVM Guest as a Network Router with Isolated Bridge

To create a KVM guest acting as a network router with an isolated bridge, you can follow the steps below:

1. Install a KVM-compatible operating system as the host system.

2. Install a guest operating system on the KVM hypervisor.

3. Configure the network interface of the host system:

   • Assign a static IP address to the host system's network interface.
   • Enable IP forwarding on the host system:

     sudo sysctl -w net.ipv4.ip_forward=1
     

     To make the IP forwarding setting permanent, add the following line to the /etc/sysctl.conf file:

     net.ipv4.ip_forward=1
     

4. Create a network bridge on the host system:

   sudo brctl addbr br0
   

5. Add the physical network interface to the bridge:

   sudo brctl addif br0 eth0
   

   Replace eth0 with the name of your physical network interface.

6. Configure the guest operating system's network interface to connect to the bridge:

   • Assign a static IP address to the guest's network interface within the subnet of the host system's network interface.
   • Set the guest's network interface to use the br0 bridge as its network connection:

     sudo nano /etc/network/interfaces
     

     Add the following lines to the file:

     auto eth0
     iface eth0 inet manual
     iface br0 inet static
     bridge_ports eth0
     address <guest_IP_address>
     netmask <subnet_mask>
     gateway <gateway_IP_address>
     

     Replace <guest_IP_address>, <subnet_mask>, and <gateway_IP_address> with appropriate values.

7. Start the network service on the guest operating system:

   sudo service networking restart
   

8. Configure the host system's firewall to allow traffic between the guest and the host:

   • Open the firewall port for the guest's network interface on the host system. For example, if the guest's network interface is eth1, open port 22 (SSH) with the following command:

     sudo ufw allow in on eth1
     

   • Ensure that the host system's firewall allows traffic between the host and the guest by configuring the firewall rules to allow traffic from the guest's IP address to the host's network interfaces.

Now, you have a KVM guest acting as a network router with an isolated bridge, allowing guest-to-guest and guest-to-host communication while maintaining safety.

References:

• KVM Networking
• Bridge Networking
• IP Forwarding
• UFW Firewall

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