AC88U Poor Upload speed on new Fibre line.

[nintenjo]

I recently upgraded from ADSL to Fibre 300 connection with Plusnet. Im supposed to get around 300down / 50up, and while i do get 300down as advertised i barely get 15-17mbps upload. Ive had a BT engineer come out today and he has run every test he can on the line and basically said its in very good health, but when they ran a remote test he said the round trip went out ok but the return was poor, so he thinks its got to be my router is the issues.

I have a Asus DSL-AC88U running the latest firmware from Asus, but I'm not sure what if any settings I can change that could affect this.. Any ideas id be welcome to try. (i dont have a spare router unfortunately as that would be my first thing).

I've attached a snip of my WAN settings as they stand ..

 

[ColinTaylor]

Try changing the MTU to 1488 or lower.

Whats the true mtu here?

Okay so coming over from sky I always used 1500 and everything was fine. Moved to plusnet and since then had really bad problems gaming on ps5. After abit of digging I came across the mtu value being 1492 for pppoe. However on the plusnet router the max mtu through CMD is 1460 so the router is...

community.plus.net

This page says that you may need to set the VLAN ID to 101 depending on your service. I'm assuming you don't need to do this as your connection mostly works already.

How to connect to broadband using your own router | Help | Plusnet

The settings you need to connect to Plusnet broadband using your own router.

www.plus.net

 

[nintenjo]

So i think i found the issue, user error. My QoS was set to a max upload of 17Mb/ps (based on my old ADSL line) so it was throttling any connection over that speed. I now get the advertised 50Mb/ps!

 

[nintenjo]

Try changing the MTU to 1488 or lower.

Whats the true mtu here?

Okay so coming over from sky I always used 1500 and everything was fine. Moved to plusnet and since then had really bad problems gaming on ps5. After abit of digging I came across the mtu value being 1492 for pppoe. However on the plusnet router the max mtu through CMD is 1460 so the router is...

community.plus.net

This page says that you may need to set the VLAN ID to 101 depending on your service. I'm assuming you don't need to do this as your connection mostly works already.

How to connect to broadband using your own router | Help | Plusnet

The settings you need to connect to Plusnet broadband using your own router.

www.plus.net

Changing my MTU to 1488 seems to have improve my upload latency as well.. So thanks again.

 

[drinkingbird]

Changing my MTU to 1488 seems to have improve my upload latency as well.. So thanks again.

I think I've heard others say BT is 1488 but to be sure, set your router back to 1500, then use ping to determine what your MTU should be.

Ping adds 28 so you have to deduct that (for example, with a 1500 MTU, 1472 is the largest ping that will get through if your ISP supports that).

To confirm if 1488 is correct, try this (after setting back to 1500 on the router)
ping -l 1459 -f google.com this would be MTU = 1487
ping -l 1460 -f google.com MTU = 1488
ping -l 1461 -f google.com MTU = 1489

Use the "MTU" of the one biggest one that succeeds. If 1460 works but 1461 gives you a fragment needed error, then 1488 is correct for MTU. If none succeed, you need to try smaller values. If they all succeed, try bigger values until you get a failure, then use the one right before that.

Add 28 to the number after "-l" to get the MTU to put in the WAN on the asus.

Note -l is lowercase "L"

I've also noticed that some interfaces don't get the updated MTU (forget which ones) until you reboot the router. I think it is the wireless ones. So safest to set it back to 1500, reboot the router, do your tests, then set it to the final number and reboot again.