bikinibottom/AIServerSetup/99-Tips-And-Tricks/02-Set Up Bridge Networking on Ubuntu for Virtual Machines.md

Guide to Set Up Bridge Networking on Ubuntu for Virtual Machines

This guide explains how to configure bridge networking on Ubuntu to allow virtual machines (VMs) to directly access the network, obtaining their own IP addresses from the DHCP server.

By following this guide, you can successfully set up bridge networking, enabling your virtual machines to directly access the network as if they were standalone devices.

---

Step 1: Identify Your Primary Network Interface

The primary network interface is the one currently used by the server for network access. Identify it with the following command:

ip link show

Look for the name of the interface (e.g., enp8s0) with state UP.

---

Step 2: Backup Your Current Network Configuration

Before making any changes, back up the existing netplan configuration file:

sudo cp /etc/netplan/00-installer-config.yaml /etc/netplan/00-installer-config.yaml.bak

---

Step 3: Configure the Bridge

Edit the netplan configuration file:

sudo nano /etc/netplan/00-installer-config.yaml

Replace its content with the following, adjusted for your environment:

network:
  version: 2
  ethernets:
    enp8s0:
      dhcp4: no
  bridges:
    br0:
      interfaces: [enp8s0]
      dhcp4: true

• enp8s0: Your physical network interface.
• br0: The new bridge interface that will be used by the virtual machines and the host.

Save and exit the file.

---

Step 4: Apply the Configuration

Apply the new network configuration to create the bridge:

sudo netplan apply

---

Step 5: Verify the Bridge Configuration

Check that the bridge br0 is active and has an IP address:

ip addr show br0

You should see an output like this:

3: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 46:10:cc:63:f4:37 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.10/24 metric 100 brd 192.168.1.255 scope global dynamic br0
       valid_lft 7102sec preferred_lft 7102sec

---

Step 6: Configure Virtual Machines to Use the Bridge

For VMs created with tools like virt-manager or virsh:

1. When configuring the VM’s network interface, choose Bridge as the network source.
2. Set br0 as the bridge interface.
3. The VM will now obtain an IP address dynamically from the same DHCP server as the host.

For virt-manager:

• Go to Add Hardware > Network.
• Choose Bridge br0 as the source.

---

Step 7: Test the Setup

1. Start a VM and ensure it obtains a dynamic IP address from the network.
2. Test connectivity by pinging the gateway or external servers from the VM.

---

Key Considerations

1. Dynamic IP for Host: The host server's IP address will now be associated with the bridge (br0) instead of the physical interface (enp8s0). This is expected behavior.
2. Backup Configuration: Always maintain a backup of your original network configuration to revert changes if needed.
3. Network Manager vs. Netplan: Use only one method (netplan or nmcli) for managing network configurations to avoid conflicts.
4. Alternative Access: If you are working on a remote server, ensure alternative access (e.g., a second network interface) before applying network changes.