Despite being packed with useful features, Proxmox has a straightforward UI that’s easy-to-learn even for beginners. But that doesn’t mean you won’t run into issues when building a home lab using this virtualization platform. Network-related problems, in particular, can rear their ugly head right after you finish installing Proxmox. Thankfully, most of these are easy to fix, and this guide will go over a myriad of solutions to help you get rid of any network issues plaguing your Proxmox server.

1 Proxmox web UI isn’t accessible after a fresh install

A common problem when setting up Proxmox on an old PC is that you may not be able to access the web GUI from another system if you enter incorrect network settings or choose the wrong device as the Management Interface during the installation process. Or perhaps, you might have forgotten to plug an Ethernet cable into the RJ45 socket on your PC when installing Proxmox.

Simple solutions to a simple problem

An easy fix is to redo the setup sequence, except, you should carefully fill in the IP address, gateway, and DNS server options. If you have another Ethernet/WLAN card or adapter plugged into your system, it’s a good idea to remove it for now. You should also ensure that you’ve used the correct port number (8006) when accessing the Proxmox host via the IP address.

2 Proxmox web UI suddenly becomes inaccessible

Let’s say you’ve been using Proxmox for a while now. But all of a sudden, you’re unable to open the web UI on another device. This problem typically occurs when you’ve changed the hardware (especially PCIe devices) on the host machine. That’s because switching the components may change the IOMMU groups, which, in turn, can change the network interface used to access the web UI. If you’ve recently updated Proxmox, it could be that the new version accidentally switched the names of the main network interface device.

Revert to the same hardware configuration

If the issue began right after switching your hardware, plug an external display into the GPU of your Proxmox host. If the monitor shows the same IP address as before, reverting to the same hardware setup as what you used when installing the virtualization environment should let you access the web UI. But for those who can’t use the original hardware, you can try the other fixes.

Set the correct IP address and Gateway settings

In case the previous fix didn't work, it’s time to fire up the nano text editor with the nano /etc/network/interfaces command. Scroll to the iface vmbr0 inet static section of the file, and make sure the address option has a static IP followed by the /24 subnet. Next, set the correct gateway before pressing Ctrl+X and tapping Y to save the file. You should be able to access the Internet after reloading the network services with the systemctl restart networking command.

Split up the IOMMU groups

Although it’s not a solution I’d personally recommend, splitting up the IOMMU groups into isolated devices could get rid of this problem. To do so, simply run the pcie_acs_override=downstream command inside the terminal. Unfortunately, this can result in stability issues later down the line, though it should allow your clients to regain access to the Proxmox web UI even with different PCIe devices slotted into the host.

3 Proxmox host can’t connect to the Internet

You may typically access the Proxmox server over the LAN, but you’re going to need access to the Internet for a variety of tasks, including downloading new container templates and updating repositories. A Proxmox host unable to connect to the Internet is almost always caused by incorrect network settings, though NIC drivers and router firmware are likely suspects as well.

Modify the firewall settings on your router

Sometimes, the Proxmox host may not even be responsible for the Internet issues. Instead, your router’s firewall might be the culprit behind your Internet woes. The actual procedure may differ vastly depending on your router, but most devices let you define the inbound and outgoing traffic rules inside the Firewall section of the Security tab.

Set the correct Ethernet interface

Another fix involves adding the main Ethernet device inside the interfaces configuration file. To do so, enter the ip addr command into the terminal on the Proxmox host and make a note of the name of the main network interface device (it should be something like enp1s0, enp2s0…). Next, open the interfaces config file by typing nano /etc/network/interfaces into the terminal, and ensure that the same Ethernet connection is used under vmbr0.

Deal with the NIC driver issues

If you’re using a 10GbE network card in your Proxmox machine, the lack of proper drivers could be why the server can’t connect to the Internet. The simplest fix for this issue is to use the built-in Ethernet port as the primary network interface on the host. But if the built-in port is busted, you can try looking into alternative solutions such as USB-to-RJ45 adapters.

4 Proxmox guests can’t connect to the Internet

Finally, we’ve arrived at the issue that gave me the most trouble in my early Proxmox days. Typically, a Proxmox virtual machine or container should connect to the Internet without issues, though incorrect IP settings, wrong network bridges, and enabling DHCP can stop the virtualized guests from ever experiencing the joys (and sorrows) of the Internet.

Fix the network bridges

Although Linux bridges require a detailed explanation in the form of a dedicated article, a quick solution involves heading to the Network tab inside your main Proxmox node. There, you’ll need to ensure the Linux bridge (often vmbr0) has the correct Ethernet connection next to the Bridge ports option. After that, ensure the virtual machine or container is using this Bridge within the Network Device option in the Hardware tab.

Set a static IP inside each guest

If you’re unable to connect to the Internet even after ensuring all the bridges are working properly, it’s time to use static IP addresses inside your virtual machines and containers.

For containers, it’s relatively simple, as all you have to do is navigate to their Network tab and enter a static IP (followed by the subnet mask) alongside the correct Gateway, and you’ll be all set.

Meanwhile, you’ll need to modify these settings inside the operating systems running on your VMs. While the exact procedure is different for each OS, most GUI systems have dedicated Network settings where you can disable DHCP and set static IPs, while their CLI-based counterparts may require you to run some commands to achieve the same result.

Keeping your Proxmox server in a tip-top shape

With that, your network problems should be a thing of the past, and you’re free to experiment with the Proxmox server to your heart’s content. If you’re looking for some cool stuff to pull off on your home lab, I recommend running some macOS virtual machines on it. Alternatively, you might want to check out our guides on enabling GPU passthrough to leverage the power of your pixel-pushing graphics card inside a virtual machine. Or you can try deploying some useful containers and virtual machines if you’re looking for more productive things to do using your Proxmox host.