The day before the fiber install, I upgraded Randy, the house server, from a 2.5-gigabit network card to a 10-gigabit one. This felt like overkill right up until I remembered the new internet plan was 5 gigabits symmetric, and a 2.5-gig card would have quietly capped the whole line at half speed. The pre-work paid off in a very specific, very stupid way I’ll get to.
Cat6 versus Cat6A
The first attempt at the 10-gig link refused to come up at all. The port kept throwing a “signal loss” alarm and negotiating down. The cable looked fine. It was fine — for a slower spec. It was Cat6, and 10-gigabit over any real distance wants Cat6A, which has the bandwidth headroom Cat6 doesn’t. The two cables are visually identical and one of them silently fails at 10 gig with no useful error. Swapped in Cat6A, link came up instantly. Write that one on your hand.
Passthrough that wouldn’t pass
Then install day. The AT&T tech — nice guy, ran fiber from outside through the attic and straight into the rack — got the gateway lit, ran a speed test off his laptop, saw five gigs, and headed out. Clean install. Except the way I have it set up, that all-in-one gateway is supposed to hand its public connection straight through to my own router so I’m not running two routers stacked on top of each other, each doing its own translation layer. And the passthrough wasn’t passing through. My router sat there stubbornly holding a useless private address from the gateway instead of the real public one. No internet for anything behind it, which was everything.
The visitor badge
Here’s the cause, and it’s a good one. The gateway only hands the real connection to one specific device — it identifies that device by its hardware address, a factory-burned ID every network port has. I’d registered my router’s main port. But the actual fiber was plugged into a different port on the same router — the high-speed one — and that port has its own, different hardware address. The gateway looked at it, didn’t recognize it, and handed it the digital equivalent of a visitor badge.
Lending it the right face
The fix is delightfully sneaky: you tell the high-speed port to impersonate the port that was registered — clone the old hardware address onto it. Now the gateway sees the ID it’s expecting, hands over the real connection, and my router grabbed the public address within seconds. The router was always allowed in. It just showed up wearing the wrong face, and I had to lend it the right one.
When the van pulls away
Final tally: 4.9 gigabits down, 4.77 up, six-millisecond ping. The old cable internet got demoted to a backup line for a 30-day trust period and then cancelled once the fiber proved it wouldn’t flinch.
A rule that keeps proving itself: the professional install ends when the tech’s laptop shows a good number. The actual install — the part where your specific setup meets the real world — starts about thirty seconds after the van pulls away.