Lenovo ThinkPad USB 3.0 Ethernet Adapter 1000 Mbit/s

The Lenovo ThinkPad USB 3.0 Ethernet Adapter (4X90E51405) is a compact wired network dongle that provides a full‑size RJ‑45 port via a USB connection. Designed for systems without a built‑in Ethernet jack, the adapter delivers up to 1000 Mbit/s over USB 3.0 and falls back to 100/10 Mbit/s on USB 2.0. The black, lightweight adapter supports booting from LAN on selected ThinkPad systems and includes activity and power LEDs on the RJ‑45 connector for connection status.

Advantages

The adapter offers Gigabit Ethernet performance when connected to a USB 3.0 port and automatic speed adaptation on USB 2.0. It uses a full‑size RJ‑45 connector with two LEDs (green for power, yellow for activity) to indicate link and transfer status. The device supports full duplex flow control (IEEE 802.3x) and conforms to IEEE 802.3, IEEE 802.3u and IEEE 802.3az standards. It is small and lightweight for easy transport and fits in briefcases or laptop bags.

Suitable for

• Ultrabooks and tablets without an RJ‑45 port
• Office or hotel environments requiring a stable wired connection
• ThinkPad systems that require PXE/boot from LAN support
• Users who need a simple plug‑and‑play wired networking solution

Key specifications

• Manufacturer part number (MPN): 4X90E51405
• Maximum data transfer rate: 1000 Mbit/s (USB 3.0); 100/10 Mbit/s (USB 2.0)
• Interface: USB (host) — Host interface: RJ‑45
• Networking standards: IEEE 802.3, IEEE 802.3u, IEEE 802.3x, IEEE 802.3az
• Full duplex flow control (IEEE 802.3x)
• Power over Ethernet (PoE): not supported
• Colour: Black — Weight: 0.045 kg

How to use

Plug the Lenovo ThinkPad USB 3.0 Ethernet Adapter into an available USB port on your laptop, tablet or Ultrabook. Connect a network cable to the full‑size RJ‑45 connector. On systems with USB 3.0 the adapter negotiates Gigabit speeds automatically; on USB 2.0 ports it will operate at 100/10 Mbit/s. For selected ThinkPad models that support network booting, enable LAN/PXE boot in BIOS/UEFI if you need to boot from a remote server.

Recommendations

Use a USB 3.0 port and a Cat5e or better Ethernet cable to achieve Gigabit speeds. Avoid relying on the adapter for power delivery—PoE is not supported. Check BIOS/UEFI settings on compatible ThinkPad systems to enable boot from LAN when required.