February 1, 2026
Scorching speeds, scorching hands
Reliable 25 Gigabit Ethernet via Thunderbolt
Tiny 25G Thunderbolt dongle sparks speed dreams—and scorch warnings
TLDR: A bargain Thunderbolt dongle pushes near-25G speeds without a power brick but runs very hot and can crash Macs; inside is a repurposed server card. Commenters are split between loving the price/performance, slamming the thermal design, and asking why not just connect Macs directly over Thunderbolt instead.
A tiny, bus‑powered Thunderbolt-to-25 Gigabit Ethernet adapter just dropped into the chat, and the community is split between “take my money” and “take my fire extinguisher.” It’s one cable, plug‑and‑play on Mac, quiet, and starts around $157—way cheaper than those big-name boxes—yet reviewers say it gets “not touchable” hot and has even nudged a few Macs into a crash (Apple says it’s not a security issue).
Numbers heads cheered at tests showing ~20.7 Gbps one way and ~25.4 Gbps when sending in both directions, which is basically the limit of what Thunderbolt can carry. But the dual‑port version won’t double your speed—Thunderbolt is the bottleneck—so it’s more for backup links than bragging rights. Then came the teardown twist: inside is a repurposed data‑center card plus a mystery Thunderbolt bridge, and on some units a tiny copper heatsink is missing. Cue the DIYers: add a heatsink, or—gasp—run it without the case. Neat freaks fainted.
The comments lit up. Nextgrid roasted the “terrible” thermal design, while others shrugged, reminding everyone that Thunderbolt is basically an external computer slot, so the power and heat are expected. Zokier tossed in a chaos grenade: you can just plug two Macs together over Thunderbolt and skip the dongle. Meanwhile, speed purists like consp were aghast it isn’t hitting a clean 25G one-way, muttering about RDMA (a trick that bypasses the CPU) like a magic spell. And cs02rm0? They sparked a meme: “Now I just need a reason to own this.”
Key Points
- •A bus‑powered Thunderbolt‑to‑25GbE adapter (“PX Thunderbolt to Ethernet”) works plug‑and‑play on macOS and is sold on Amazon in single and dual SFP28 versions starting around $157.
- •The device is silent and needs no external power but runs extremely hot; the author observed occasional network dropouts and macOS kernel panics, which Apple said were not security issues.
- •Measured with iperf3, throughput reached ~20.7 Gbit/s one way and ~25.4 Gbit/s bidirectional, near practical limits for PCIe over Thunderbolt 3/4.
- •Native PCIe 25GbE links between Linux machines achieved ~23.5 Gbit/s per direction (~12% better one‑way and ~85% higher aggregate than the Thunderbolt setup).
- •A teardown revealed a Mellanox ConnectX‑4 Lx EN OCP 2.0 NIC paired with an OCP‑to‑Thunderbolt 3 bridge board; heatsink placement is poor, and a copper heatsink was missing on one dual‑port unit.