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QLFilter

QLFilter is an optional host-level anti-DDoS filter for Quake Live servers. It drops reflection network traffic before it ever reaches the QLDS process.

The Problem It Solves

Public-facing QLDS UDP ports can be targeted by malicious actors with junk or reflected UDP traffic. This can include DNS, SSDP, and similar amplification/reflection packets sent at the server rather than legitimate player traffic. At high enough volume, these attacks can waste bandwidth, add load, and interfere with real game traffic.

How It Works

QLFilter operates at a very low level in Linux using eBPF and XDP — the eXpress Data Path. XDP hooks into the network driver itself, before the packet even enters the Linux networking stack. Packets that match known junk patterns (DNS, SSDP, and similar reflection garbage) are dropped at wire speed, before they consume CPU or reach QLDS.

The result: your Quake Live server only sees legitimate player traffic.

Installation

QLFilter is installed per host, not per instance. All instances on a host share one QLFilter installation.

  1. Go to Servers.
  2. Open the host's Actions menu.
  3. Click Install QLFilter.

  1. Wait for the status indicator to show Active.

While QLFilter is installing, other host management actions are temporarily locked.

Uninstallation

  1. Open the host's Actions menu.
  2. Click Uninstall QLFilter.

  1. Wait for the status to return to Not Installed.

Status Reference

Status Meaning
Not Installed QLFilter is not present on this host
Installing Install in progress — host actions locked
Active QLFilter running and filtering
Inactive Installed but not currently running
Uninstalling Removal in progress
Error Install or uninstall failed — see Deployment Troubleshooting