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Le Sanctum

2026-06-19: The Speed Test That Cried Slow

A pencil sketch on a dark background: a large speedometer gauge with its needle stuck low near the bottom, while behind and around it an enormous torrent of light-streaks and data rushes past unmeasured and uncaught; a single teal accent glow lights the gap between the tiny measured trickle and the vast real flow

Eight gigabits per second, symmetric, on glass. The speed test said 1.86 down, 0.88 up. Disappointing — until you look closer and realize the number was never about the line.

The tell

Section titled “The tell”

The upload gives it away. The plan is symmetric — 8 up, 8 down — but the test showed 0.88 Gbps up, barely a gigabit. A real 8-gig line, measured honestly, shows gigabits in both directions. 0.88 isn’t your fibre; it is the measuring instrument hitting its own ceiling. That test ran on the ISP gateway’s modest CPU, over a single connection, to a single server. Every one of those is a throttle that has nothing to do with the glass outside.

Three lies a speed test tells

Section titled “Three lies a speed test tells”
  • A single TCP stream tops out around 2 Gbps — regardless of the line — because of latency and window math. One connection to one server cannot fill a multi-gig pipe. (PCWorld measured the same line at ~2 Gbps single-server vs ~8 Gbps multi-server.) The hub’s built-in test, a browser test, an ad-hoc curl: all single-ish-stream, all land near 2.
  • Wi-Fi caps you at ~1-2 Gbps before the line is ever in question. Test over Wi-Fi and you are measuring the air, not the fibre.
  • The chain is only as fast as its slowest port. A 1G switch, a 2.5G NIC, a cable in the wrong jack — any one of them is your real ceiling, and no line upgrade moves it.

And the one that sends people down rabbit holes: single-NAT vs double-NAT changes none of this. NAT is a table lookup, not a toll booth. Chasing your NAT topology to go faster is chasing a ghost. (PPPoE, ironically, can slow you down — it is CPU-bound and caps a prosumer router around 3-3.5 Gbps.)

The fix is a test that tells the truth

Section titled “The fix is a test that tells the truth”

So we built one. sanctum net speedtest runs a multi-stream test alongside a single-stream one — and shows you the gap, so the lie is visible:

single stream: 1.8 Gbps    multi-stream: 7.9 Gbps
=> the line is fine; the old test was the problem.

It reads the link speed of every hop it can see — your NIC, Wi-Fi vs wired, the router’s ports — and names the bottleneck instead of leaving you guessing. Run it with --no-test and it skips the download entirely, just auditing the ceiling and explaining it. On a laptop on Wi-Fi it says the quiet part out loud: “On Wi-Fi: yes -> caps ~1-2 Gbps. Go wired to see your real speed.”

No faster line required. Just an honest number.