Troubleshooting Proxmox: Resolving Network Issues with Same Linux Server Bridges

Configuring networks in Proxmox can sometimes present challenges, especially when dealing with multiple network bridges on the same Linux server. Let’s explore a common scenario where users encounter difficulties setting up a secondary bridge on the same network as their primary Proxmox management interface. This article aims to clarify potential issues and guide you through troubleshooting steps to ensure your Proxmox network configuration works as expected.

One Proxmox user outlined a setup involving multiple network ports and bridges, aiming to isolate network traffic while maintaining accessibility on the same network. Their configuration included:

• vmbr0: Integrated Realtek NIC for management on the 192.168.1.x network.
• vmbr1: Dedicated 10GB Intel NIC port directly connected to NAS.
• Dedicated port passed through to a Windows 10 VM for direct NAS access.
• Dedicated port passed through to a Windows 10 VM for NVR on a separate VLAN.
• vmbr2: A secondary bridge intended for a separate network pipe on the same 192.168.1.x network, hosting a speedtest server in an LXC container.

The core issue arose when the user attempted to use vmbr2 for their Linux container. While the container worked perfectly fine on vmbr0, switching it to vmbr2 resulted in a loss of network connectivity. The container received an IP address but couldn’t access the internet, nor could devices on the network ping it. The vmbr2 configuration was defined as follows:

auto vmbr2
iface vmbr2 inet static
    address 192.168.1.129/24
    bridge-ports enp11s0
    bridge-stp off
    bridge-fd 0

Despite being able to ping the vmbr2 bridge IP (192.168.1.129), the LXC container remained unreachable. This raises a crucial question: Is it indeed possible to operate two Linux bridges on separate ports within the same network on a Proxmox server? The answer is yes, it is absolutely possible, and it’s a common practice for network segmentation or traffic management. The problem likely lies within the configuration details.

Here are potential areas to investigate when troubleshooting similar Proxmox network configurations:

1. Interface and Bridge Port Assignment: Double-check that enp11s0 is indeed the correct physical interface you intend to use for vmbr2. Incorrect interface assignment is a frequent cause of network issues. Use commands like ip a or lspci within the Proxmox host to verify your network interface names and their status.

2. Subnet Mask and Gateway: Ensure the subnet mask (/24 in this case) is consistent with your network. While not explicitly mentioned as a problem, incorrect subnet masks can lead to communication failures. For devices on the same 192.168.1.x network, a /24 mask is typical. Gateway configuration is usually handled by the main network interface (vmbr0 in this case). Since vmbr2 is on the same network, it generally doesn’t need a separate gateway unless you are implementing more complex routing policies.

3. Firewall Rules: Proxmox firewall, or any firewall within the LXC container, could be blocking traffic. Temporarily disable firewalls on both the Proxmox host (if configured) and within the LXC container to test if this is the source of the problem. Remember to re-enable firewalls after troubleshooting.

4. DHCP vs. Static IP: The user mentioned assigning a static IP. If you are using static IPs, ensure there are no IP conflicts on your network. If you are relying on DHCP for LXC containers on vmbr2, verify that your DHCP server is configured to serve IPs to devices connected to this bridge, or that DHCP relay is correctly set up if the DHCP server is on a different segment. However, for a container on the same network as the host, typically DHCP from the main network router should suffice if vmbr2 is correctly bridged.

5. Routing and Network Segmentation: While the goal is to be on the same network, inadvertently creating a routing issue or network segmentation could cause problems. For a simple setup like this, routing issues are less likely unless there’s a more complex network topology involved beyond what’s described.

In conclusion, setting up multiple bridges on the same network in Proxmox for different purposes is achievable and a powerful feature for network management. When facing connectivity issues like the one described, systematically checking interface assignments, network configurations, firewall rules, and IP addressing schemes will usually pinpoint the root cause and lead to a resolution. Remember to test incrementally and revert changes if necessary to maintain a stable Proxmox environment.