What is vmbr0 in proxmox?

In Proxmox VE, vmbr0 is the default and most commonly used virtual network bridge. It functions as both a Linux Bridge (acting like a virtual network switch) and an interface for your Proxmox OS, serving as the primary network connection point for your Proxmox host and its virtual machines (VMs) and containers (LXCs).

Understanding vmbr0 as a Linux Bridge

A Linux Bridge, conceptually, is much like a physical Ethernet switch. It allows multiple network interfaces, both physical and virtual, to connect and communicate with each other on the same network segment.

Virtual Switch Functionality: vmbr0 enables your Proxmox host to act as a central hub for all its virtualized guests. VMs and LXCs connect their virtual network cards to vmbr0, allowing them to communicate with each other, with the Proxmox host, and, crucially, with the external physical network.
Connecting to Physical Network: Typically, vmbr0 is configured to "bridge" a physical network interface card (NIC) of your Proxmox server, such as enp0s31f6 or eth0. This means that traffic from your VMs and LXCs that connect to vmbr0 can pass through this physical NIC to reach the internet or other devices on your local network, and vice-versa.

vmbr0 as the Proxmox Host's Interface

Beyond its role as a virtual switch for guests, vmbr0 is also the interface where the Proxmox host itself obtains its network identity.

Host Networking Configuration: When you configure network settings like the IP address, subnet mask, and gateway for your Proxmox server, you are doing so on vmbr0. This makes vmbr0 the network interface through which your Proxmox host communicates with the network, including accessing package repositories, management via the web interface, or SSH.
Single Gateway: It's important to note that the Proxmox host, like any operating system, can only have one default gateway for routing external traffic. This gateway is configured on vmbr0, making it the primary exit point for your Proxmox server's own network communications.

Practical Implications and Configuration

Configuring vmbr0 is a fundamental step in setting up any Proxmox VE server, as it dictates how your host and its guests will interact with the network.

Default Setup: During Proxmox installation, vmbr0 is usually set up by default to bridge your primary physical network adapter and configured with an IP address, netmask, and gateway.
Network Configuration Example (/etc/network/interfaces):
Proxmox uses a standard Debian network configuration file located at /etc/network/interfaces. A typical vmbr0 entry might look like this:
```
auto vmbr0
iface vmbr0 inet static
    address 192.168.1.10/24  # Your Proxmox host's IP address and subnet
    gateway 192.168.1.1     # Your network's default gateway
    bridge-ports enp0s31f6  # The physical NIC connected to vmbr0
    bridge-stp off
    bridge-fd 0
```
In this example:
- address defines the static IP address and CIDR subnet for the Proxmox host.
- gateway specifies the default router for the Proxmox host.
- bridge-ports enp0s31f6 indicates that the physical network adapter enp0s31f6 is connected to this virtual bridge.
Proxmox Web Interface: You can easily manage and modify vmbr0's settings directly from the Proxmox web interface under Datacenter > Your_Node_Name > System > Network.

Summary Table of vmbr0 Roles

Aspect	vmbr0's Role	Description
Linux Bridge	Virtual Network Switch	Connects VMs, LXCs, and the physical network interface, allowing traffic to flow between them. Similar to a physical Ethernet switch.
Host Interface	Primary Network Interface for Proxmox Host	Carries the IP address, subnet mask, and gateway settings for the Proxmox server itself, enabling its own network communication.
Gateway	Default Gateway for Proxmox Host	The network settings configured on `vmbr0` include the default gateway that the Proxmox host uses to route traffic to external networks (e.g., the Internet).
Guest Connectivity	Connection Point for VMs/LXCs	Virtual machines and containers attach their virtual network adapters to `vmbr0` to gain network access, both internal and external.
Physical Link	Bridges Physical NIC	Typically linked to one of the server's physical network interface cards (e.g., `eth0`, `enp0s31f6`) to provide external network connectivity for all connected devices.

For more in-depth information on network configuration in Proxmox, refer to the official Proxmox VE documentation.