Could be, but worse than that: I'm guessing there was a bug where sometimes the frags wouldn't get combined properly, the payload was corrupted but the TCP checksum gets recalculated against the corrupt data.

In reply to a post by jchamier:

Interesting, the advice on DSLreports and other sites for over 10 years has always said to never change the router, always change the PC. Otherwise you just cause the router more work

Yeah but by changing the router's setting, you're matching the local MTU to the maximum PMTU, which should make it easier on the cheap plastic router, not harder.

Or I might be overthinking it.

By all means hardcode your Windows or macOS stack as well, but that's probably just gilding the lily (and as you say, you can't do it on most of your other devices at home).

In reply to a post by RobertoS:

Not for me it didn't.

Me neither. YouTube is noticeably smoother and more consistent now.

I guess we're not dealing with a single issue then.

With my problems it was very consistent over several months:

- random websites needing lots of TCP connections would often stall
- streaming connections were basically never impacted (there was never any buffering on several hours of video streaming each evening)
- VPN connections were never impacted

Edited by andynormancx (Sat 12-Sep-20 17:25:44)

In reply to a post by richi:

Yeah but by changing the router's setting, you're matching the local MTU to the maximum PMTU, which should make it easier on the cheap plastic router, not harder.

Or I might be overthinking it.

I don’t think there is any point changing the router. The PMTU may be higher or lower as it is the combination of networks (not just the ISP) that your traffic routes through, to get to the service you are after.

By all means hardcode your Windows or macOS stack as well, but that's probably just gilding the lily (and as you say, you can't do it on most of your other devices at home).

I also don’t see the benefit changing the router. PMTU will handle the networks.

Performance is still good. Websites load quickly and no sign of the previous stalling issues. One odd thing though - three days ago I was getting solid 80Mbps upload however, over the weekend, 18Mbps is the max I can get.

In reply to a post by andynormancx:

I guess we're not dealing with a single issue then.

Might not be as cut'n'dried as this though. Some streaming services open more than one parallel connection—YouTube for example.

In reply to a post by jchamier:

The PMTU may be higher or lower as it is the combination of networks (not just the ISP) that your traffic routes through, to get to the service you are after.

I'm confused. How can it be higher?

In reply to a post by richi:

How can it be higher?

Higher than your test, as your target will be a different network / host.

In reply to a post by jchamier:

In reply to a post by richi:

How can it be higher?

Higher than your test, as your target will be a different network / host.

But on the assumption that 1400 is now the limit for DF packets within Three's core, PMTU Discovery surely will cap at 1400, no?