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OpenWrt Routers × ALFA Network Configuration & Limitations Guide

Quick Summary: Adding an external ALFA USB adapter to OpenWrt routers (including GL.iNet travel routers, x86 soft routers, and Raspberry Pi gateways) creates a dedicated secondary WAN (WISP repeater), high-gain AP hotspot, or dedicated wireless sniffer node. The ALFA AWUS036AXML (MT7921U) is supported via package feeds in OpenWrt 22.03.3+ (kernel 5.10 backport) and 23.05+ (kernel 5.15), while AWUS036ACM (MT7612U) is supported across all branches. This guide covers setup and discloses upstream GitHub Issue #839 (Active Monitor Lockup).

1. Kernel & Compatibility Matrix​

ALFA ModelChipsetOpenWrt 22.03.3+OpenWrt 23.05+Required Kernel Packages
AWUS036ACMMediaTek MT7612U✅ Fully Supported✅ Fully Supportedkmod-mt76x2u mt76-firmware
AWUS036AXMLMediaTek MT7921AUN✅ Supported (Known Bug)✅ Supported (Known Bug)kmod-mt7921u
AWUS036ACHMMediaTek MT7610U✅ Fully Supported✅ Fully Supportedkmod-mt76x0u
AWUS036ACHRealtek RTL8812AU❌ Not in official feed❌ Not in official feedRequires building custom out-of-tree package

2. Package Installation & Wireless Setup​

# 1. Update package database
opkg update

# 2. Install kernel modules for your ALFA adapter
# For AWUS036AXML (Wi-Fi 6/6E):
opkg install kmod-mt7921u kmod-mt76-core wireless-tools usbutils

# For AWUS036ACM (802.11ac):
opkg install kmod-mt76x2u kmod-mt76-core wireless-tools usbutils

# 3. Detect and generate configuration
wifi config >> /etc/config/wireless

# 4. Restart network stack
/etc/init.d/network restart

3. Crucial Upstream Limitations & Bug Disclosure​

⚠️ Upstream Bug: AWUS036AXML Active Monitor Crash (Issue #839)​

  • Symptom: Enabling active monitor mode and continuous frame injection (e.g. aireplay-ng --deauth) on mt7921u under OpenWrt causes the driver to lock up within seconds (mt7921u: failed to send tx packet).
  • Root Cause: Upstream openwrt/mt76 Issue #839 (DMA concurrency locking error in 5.10/5.15 kernels).
  • Engineering Recommendation:
    1. For passive packet capture (Kismet / tcpdump), AWUS036AXML works normally.
    2. For high-rate packet injection / deauth testing, use ALFA AWUS036ACM (mt76x2u).

⚠️ 6 GHz Configuration Status​

Current LuCI Web UI (OpenWrt 23.05) lacks complete 6 GHz channel selectors. AWUS036AXML operates primarily as an ultra-high performance 2.4 GHz / 5 GHz radio under OpenWrt.