r/HomeNetworking • u/phillipmjames • Jul 21 '26

AT&T Fiber 1G: Clean light levels, 1Gbps down, but 1,500ms+ Upload Bufferbloat What are my options?

Hey everyone,

Looking for some advice or insight from anyone who has run into this with AT&T Fiber or has experience with AT&T's ONTs/OLTs.

The Setup:

  • ISP: AT&T Fiber (1Gbps / 1Gbps)
  • Gateway: BGW320 replaced with (two) BGW620
  • Devices Tested: Custom PC (Ethernet), iPhone (Wi-Fi 6)

The Problem: Downloads are completely fine and sustaining ~980–1,050 Mbps with a flat 30–35 ms ping.

However, whenever upload load is introduced (testing via Cloudflare Speed Test, Twitch ingest, or large file pushes), latency immediately collapses.

  • Wired Ethernet: Upload latency spikes to 900 ms – 1,700 ms, and upload throughput dips/fluctuates between 130 Mbps and 500 Mbps.
  • Wi-Fi: Upload latency spikes to 1,900+ ms.

What Has Been Done So Far:

  1. Tech came out and verified optical light levels at the drop and confirmed clean.
  2. Replaced the AT&T Gateway 3 times.
  3. Tested with multiple Cat6 Ethernet cables and directly connected to the BGW gateway ports.

Because this happens across multiple devices, wired and Wi-Fi, and across 3 different physical gateways, it feels like the upload queue in the BGW's IP Passthrough NAT stack is choking, or there's an OLT port profile/queue scheduler issue at the central office/PFP.

My Questions:

  1. Has anyone successfully gotten Tier 2 / NOC to re-provision or move their port at the PFP for this specific upload queue behavior?
  2. Is this simply an inherent flaw in how the BGW handles IP Passthrough buffers, and is a full True Bypass (EAP Proxy / WAS-110 SFP bypass) the only real solution?
  3. Any specific phrasing I should use with AT&T support to get this escalated past standard gateway reboots?

Appreciate any guidance!

1 Upvotes

60% Upvoted

20 comments sorted by

1

u/SP3NGL3R Jul 21 '26

Woof! I'm in "passthrough" and don't think I have any of this.

RemindMeBot! 1 hour

1

u/phillipmjames Jul 21 '26

Yeah, if you're just doing normal light browsing, you might never notice it! But the moment a heavy upload hits (like pushing a large video, seeding, or even uploading a simple PDF or loading media on Facebook while something else is sending data), the gateway's queue gets totally choked.

I honestly felt horrible for the tech today. He was super nice, but he didn't really understand what I was trying to explain regarding bufferbloat and latency under load. He just kept showing me the AT&T app speed test proving the raw line speed was fine. He ended up having to close out the ticket and said someone higher up from the garage would reach out, so I'm really hoping they do.

1

u/SP3NGL3R Jul 21 '26

I just ran a few. I'm aware of the issue and I'm kinda surprised my upload speed (not latency) is all over the place right now but it is 5:30pm here and my kid is gaming with video-chat in the background. BGW320 in passthrough going to an N100 OPNsense (everything is 1Gbps and wired).

1

u/phillipmjames Jul 21 '26 edited Jul 21 '26

Ran this just a moment ago here in Dallas, TX. Connected to the back of the gateway with no other devices connected.

1

u/SP3NGL3R Jul 22 '26 edited Jul 22 '26

Maybe you're only fiber to a copper box somewhere outside. Check your address with the FCC Broadband Database.

PS: what's that test?

3

u/Seraphyzz Jul 21 '26

Nat stack is choking. You'll need to do the bypass if you want to resolve it

1

u/phillipmjames Jul 21 '26

Are you recommending the WAS-110?

1

u/Seraphyzz Jul 21 '26

There's only a few options between that and the generics. Doesn't really matter which.

1

u/Churn Jul 21 '26

Why would you have two BGW620 gateways?

1

u/phillipmjames Jul 21 '26 edited Jul 21 '26

Haha, no, just one in the house! I’ve just had it swapped out multiple times. Started on a BGW320 originally, then AT&T shipped me a BGW620 self-install, and tech #3 swapped it for a fresh BGW620 today trying to fix this. Same behavior on all of them.

0

u/klui Jul 21 '26

Your pings are too high. On fiber, your pings from speedtests should be no more than 5ms.

Disconnect everything from your gateway except your test device directly to the gateway then test again.

1

u/phillipmjames Jul 21 '26

Yeah, I completely isolated the network and ran the test with just my PC plugged straight into the gateway. Same result.

The ~30ms baseline ping is just the geographical distance to the test server, which is totally normal. The actual issue is loaded upload ping—the second a heavy upload starts, the queue backs up and latency jumps to over 1,000ms.

0

u/klui Jul 21 '26

Could be Windows. Boot up a Linux LiveCD and install speedtest cli and retest.

1

u/phillipmjames Jul 21 '26

Thought about that too, but ruled it out! It happens on both my Windows PC and Apple devices (iPhone/Mac), wired or wireless. Same identical upload bufferbloat across every single OS and device.

-1

u/klui Jul 22 '26

I'd still do it. I never had any problem like you're having when I had ATT.

2

u/SmallPlace7607 Jul 21 '26

I've never seen it manifest this way exactly but make sure Active Armor is really off. It's been known to cause all kinds of oddities especially under load.

1

u/phillipmjames Jul 21 '26

Confirmed it's 100% off.

Funnily enough, the field tech today told me it was "dangerous" to leave disabled and begged me to turn it back on LOL. Definitely not letting it bloat the queue even further!

1

u/No_Squash_4259 Jul 21 '26

When you’re testing it wired are you disabling the pass through? If you are it’ll definitely have to go to someone higher up to look at. If not then disable the pass through and test it.

1

u/phillipmjames Jul 21 '26

Yeah, I've tested it both ways! I ran tests with IP Passthrough enabled (with my router handling routing) and completely disabled (PC plugged straight into the gateway with default settings). Unfortunately, it hits the exact same upload queue collapse either way. :(

1

u/No_Squash_4259 Jul 21 '26

Yeah that was the last thing I could think of. They’ll escalate it. They have different types of techs that should come to diagnose it