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Proxmox Networking

Network Interfaces

A network interface is a thing on Linux that can send/receive network traffic. It can be:

  • Physical: a real NIC/port
  • Virtual: created by software (bridge, VLAN interface, VM tap device, container veth, etc.)

[!NOTE] A network interface is like a mailbox slot. Each slot has its own label so the post office (Linux) knows which slot to deliver packets to.

Modern Linux uses predictable network interface names (instead of old eth0, eth1, ...). These names are based on hardware location to make them stable across reboots and hardware changes.

Example: enp1s0

  • en = Ethernet (wired networking)
  • p1 = device is on PCI bus path 1 (hardware location)
  • s0 = slot/function index at that PCI location

Common prefixes

Prefix Interface type
en Wired Ethernet
wl WLAN, wireless local area network, WiFi
lo Loopback adapter.

[!NOTE] Loopback adapter is used for connections that should not be routed outside one computer. Every computer calls itself "localhost", which resolves to IP address 127.0.0.1. IPv4 local addresses are 127.0.0.1/8, and IPv6 local addresses are ::1/128.

Examples of common network interface names

Interface Explanation
wlp4s0 WiFi card
enp1s0 Wired ethernet card
lo Loopback adapter
enx738899738899 Ethernet interface named by MAC address (very common for USB Ethernet adapters)

To view your interfaces, use the command ip link show. This lists all interfaces, their status (up/down), and MAC addresses.

Linux Bridges in Proxmox

A Linux bridge (often named vmbr0, vmbr1, etc., in Proxmox) is a software-based Layer 2 (Ethernet) switch that runs inside your Proxmox host. It connects multiple network devices or interfaces together, allowing them to communicate as if they were on the same physical network segment.

  • Physical NIC (e.g., enp1s0): Acts as the uplink cable connecting to your real router or switch.
  • Bridge (e.g., vmbr0): A virtual switch inside Proxmox that multiple devices can plug into.
  • VMs or LXCs (Containers): Virtual devices connected to this switch, like computers plugged into a physical switch.

The bridge enables efficient sharing of physical network resources among your virtual guests (VMs and containers).

What's Happening Under the Hood

When you attach a VM to a bridge like vmbr0:

  • Proxmox creates a virtual "port" called a TAP device (e.g., tap100i0 for VM ID 100).
  • For LXCs, it creates a veth pair (e.g., veth100i0 on the host side, connected to the container).
  • These virtual ports are added to the bridge, just like plugging Ethernet cables into switch ports.
  • The bridge forwards Ethernet frames (Layer 2 packets) based on MAC addresses, learning where devices are located (similar to how a real switch operates with a MAC address table).

You can inspect bridges with ip link show type bridge.

Why Use a Bridge in Proxmox?

  1. Guests on Your Real LAN:

  2. VMs and containers can get IPs directly from your router's DHCP server, just like physical devices.

  3. They're reachable from other LAN devices (e.g., your laptop can ping a VM).

  4. Full internet access without extra configuration.

  5. Resource Sharing:

  6. Multiple guests share one (or more) physical NICs efficiently.

  7. Without a bridge, assigning a physical NIC to a single guest (passthrough) wastes resources, or you'd need complex routing setups.

  8. Flexibility:

  9. Supports VLANs for network segmentation (e.g., tag traffic with VLAN IDs).

  10. Can bond multiple physical NICs for redundancy or higher bandwidth (using Linux bonding).

Typical Proxmox Bridge Setup (in /etc/network/interfaces)

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auto lo
iface lo inet loopback

iface enp1s0 inet manual  # Physical NIC: Don't assign IP here; let the bridge handle it

auto vmbr0
iface vmbr0 inet static
    address 192.168.88.10/24  # IP for the Proxmox host itself
    gateway 192.168.88.1      # Your router's IP
    bridge-ports enp1s0       # Attach the physical NIC as a port
    bridge-stp off            # Disable Spanning Tree Protocol (usually not needed in simple setups)
    bridge-fd 0               # Forwarding delay: 0 for instant forwarding

After editing, apply changes with ifreload -a or systemctl restart networking.

This setup makes vmbr0 the main interface for the host and guests. Attach VMs/LXCs to vmbr0 in their network settings for bridged mode.