A Case of Proxmox Networking: VLANs, MTUs and a hint of SDN

Proxmox remains a popular choice for virtualization, yet its advanced networking features can lead to subtle, but significant challenges like Inconsistent MTU settings, unintended Docker defaults, and extra firewall interfaces (fwbr). Addressing these can significantly improve system performance and reliability.

This proposal aims to:

• Identify different network configurations possible with Proxmox

• Provide Practical Solutions to challenges caused by misconfiguration

• Share Best Practices

The topics would be:

1. MTU Mismatches

Differences in Maximum Transmission Unit (MTU) settings between Proxmox bridges and virtual machines can lead to packet fragmentation or loss. Ensuring consistent MTU settings across all knobs solves this.

2. Docker Integration in Proxmox SDN

Default Docker network configurations may not align with Proxmox’s Software Defined Networking (SDN), causing connectivity issues wherein adjusting Docker’s network settings to match Proxmox SDN parameter would be the solution.

3. Managing fwbr Interfaces

Proxmox firewall can be a bit annoying to use, with a lot of users opting for a out-of-band firewall. Regardless of its use though, unnecessary firewall bridge (fwbr) interfaces can complicate network configurations and introduce overhead.

4. VLAN Configuration

VLANs can be entirely implemented using software or used on bridges to match the ones that are defined in actual network switches. Tweaking this configuration is crucial for traffic flow to be consistent and smooth.

By presenting these topics, I expect the audience may be perplexed but they are going to be left with a plethora of knowledge around Proxmox networking, and learning is what a linux-fest is about!