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

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+### **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:
+
+```bash
+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:
+
+```bash
+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:
+
+```bash
+sudo nano /etc/netplan/00-installer-config.yaml
+```
+
+Replace its content with the following, adjusted for your environment:
+
+```yaml
+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:
+
+```bash
+sudo netplan apply
+```
+
+---
+
+#### **Step 5: Verify the Bridge Configuration**
+Check that the bridge `br0` is active and has an IP address:
+
+```bash
+ip addr show br0
+```
+
+You should see an output like this:
+
+```plaintext
+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.
+