Severe Latency Issue

[#1]

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@silkster365 wrote:

I’m reluctant to start changing the whole network topology

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The other way of looking at moving the routing to the Deco now, is that it will be good preparation and future-proofing for when FTTP becomes available to you in the next three years, as your upgrade will literally be unplug the ethernet cable from the Plusnet router (in bridge mode) and plug that same cable directly in to the new Openreach FTTP ONT,  with no other configuration changes needed, job done !

[#2]

Thanks again I ran the Waveform test as suggested. It's pretty conclusive:

Grade F

Idle latency: 17ms
Download active: +76ms
Upload active: +980ms
Download: 17.2Mbps
Upload: 2.46Mbps

During the upload test the median latency was ~1001ms, 95th percentile ~1373ms and max ~1377ms.

Test link: https://www.waveform.com/tools/bufferbloat?test-id=58d635c2-c441-488d-a620-dab41ae8365d

So yes, that certainly seems to confirm your bufferbloat diagnosis.

I'll set up the ThinkBroadband BQM as well.

[#3]

@silkster365 

I asked AI to double check that my proposed reconfiguration of your Deco and Hub Two would achieve what you're aiming for, and to produce step by step instructions for you to follow, including how to access the Deco's QoS, and what additional things you would need to do in order to still access the Plusnet Hub Two's GUI from the Deco's LAN so that you can view the VDSL line statistics (including sync speeds, SNR, error counters etc)

.

Yes, this is a clean and practical setup for FTTC. The Plusnet Hub Two becomes a pure bridged modem, the TP-Link Deco AC1300 becomes the main router (with its QoS / bandwidth controls available for anti-bufferbloat), and physical placement stays the same. There is one small cable change on the Deco itself.

Note on Deco QoS vs true bufferbloat control: Deco’s QoS lets you set total bandwidth limits and prioritise devices/apps. This can help reduce bufferbloat symptoms by preventing the connection from being fully saturated. It is not full SQM (Smart Queue Management / CAKE / fq_codel). If residual latency under load remains high after setting realistic limits (typically 85–95 % of measured speeds), a router with proper SQM would be needed later. For many people the Deco controls are still a worthwhile improvement.

Recommended order of work

Do the Hub Two first while you still have easy access, then reconfigure the Deco.

Part 1 – Put the Plusnet Hub Two into Bridge Mode

1. Connect a computer to the Hub Two by Ethernet (any LAN port 1–3) or temporarily via its Wi-Fi.
2. Open a browser and go to http://192.168.1.254. Log in with the admin password (on the pull-out card or sticker).
3. Go to Advanced Settings → Broadband.
4. Scroll to the bottom and enable Bridging / Bridge Mode.
5. Save. The Hub Two restarts and the status light turns pink/purple. Wi-Fi and routing are now disabled. The grey DSL cable stays connected to the master socket exactly as before.

Part 2 – Reconfigure the TP-Link Deco AC1300 (from Access Point to Router mode)

Cable change (only change required) Unplug the Ethernet cable that currently runs from a Hub Two LAN port into a LAN port on the main Deco unit. Plug that same cable into the WAN / Internet port on the main Deco unit instead. All other wiring and physical positions stay the same.

1. Open the Deco app on your phone (make sure you are connected to the Deco Wi-Fi if possible, or connect the phone by Ethernet temporarily if needed).
2. Go to More → Advanced → Operation Mode.
3. Change from Access Point to Router (sometimes labelled “Wi-Fi Router” or “Wireless Router”).
4. Confirm and let the Deco system reboot (usually 1–2 minutes). The LED should return to solid green/white.
5. After reboot, go to More → Internet (or Internet Connection / IPv4).
6. Set the connection type to PPPoE.
7. Enter:
   • Username: [email protected] (the broadband username)
   • Password: the password you use to log into Plusnet My Account
8. Leave VLAN / IPTV / 802.1Q disabled / off / blank / 0. (The Hub Two already handles the VLAN tagging.)
9. Save / Apply. The Deco should negotiate the PPPoE session and obtain a public IP address.
10. Once online, go to the QoS section in the Deco app:
    • Enable QoS.
    • Set Total Bandwidth to roughly 85–95 % of your actual measured download and upload speeds (run a few speed tests first to get realistic numbers).
    • Optionally prioritise important devices or activities (gaming, video calls, etc.).

Your devices will now get IP addresses from the Deco (usually in the 192.168.68.x range by default). The old Hub Two Wi-Fi network disappears.

Part 3 – Access the Hub Two GUI (DSL line stats) from the Deco network

The Hub Two keeps its management IP of 192.168.1.254 even in Bridge Mode. Because the Deco is now on a different subnet, you need a simple extra step so devices on the Deco side can reach it.

Easiest permanent method (recommended) Run a second short Ethernet cable from any free LAN port on the Hub Two (ports 1–3) into any free LAN port on the main Deco unit. This creates a direct management path without affecting the WAN connection.

Then, on any computer connected to the Deco (Wi-Fi or Ethernet):

• Open a browser and go to http://192.168.1.254.
• You should reach the Hub Manager.
• Look under Advanced Settings → Technical Log (or Status / Broadband) for sync speed, SNR margins, error counts, uptime, etc.

Alternative temporary method (no second cable) On a computer connected to the Deco:

1. Set a temporary static IP on the computer in the 192.168.1.x range (e.g. 192.168.1.10, subnet mask 255.255.255.0, no gateway needed).
2. Browse to http://192.168.1.254.
3. When finished, switch the computer back to automatic/DHCP.

If the second cable method is used, the Hub Two’s IP stays reachable at any time for quick checks of line quality.

Quick checklist after everything is done

• Hub Two light is pink/purple.
• Deco is in Router mode and shows a public IP on its WAN status.
• Internet works on both wired and Wi-Fi devices connected to the Deco.
• QoS bandwidth limits are set a little below real line speed.
• You can reach http://192.168.1.254 (via the second cable or temporary static IP) and see DSL stats.

Reversing the changes (if needed)

• On the Deco: change Operation Mode back to Access Point and move the Ethernet cable back to a LAN port on the Deco.
• On the Hub Two: either disable Bridge Mode in the Hub Manager or factory-reset it (paperclip in the reset hole for ~20–30 seconds).

This keeps everything in the same physical locations, minimises cabling changes, and gives you the bandwidth controls on the Deco while still allowing easy access to the Hub Two’s line statistics.

[#4]

@ExForce9 

So more thinking is required on Hub two management.

Easiest permanent method (recommended)

Some years back I tried that method of connecting up a monitor, everything locked up.

The Hub was 192.168.1.254 TP-Link router DHCP address pool was 192.168.10.0/24 without any deep thinking thoughts I could only assume some sort of network loop was created with the router WAN and LAN ports going to the same switch.

My final solution was the Alternative temporary method.

[#5]

You are most likely correct.

I did hesitate when I saw two different subnets sharing the same LAN switch, and wondered what would happen, but assumed the AI had a better understanding of such things.

Until recently, I've always configured my routers to have a defined static route between the LAN and a different 'modem' subnet on the router's WAN port for http/https access to the modem GUI, simultaneously with the same WAN cable passing the PPP traffic to and from a single port modem.  I doubt if this level of static routing can be achieved using the Deco.

Today I use a two ethernet port DrayTek Vigor 167, where port "P1" goes to my router's WAN, and the second port "P2" goes to a spare network LAN port, now the modem's GUI can be accessed on the same subnet as the LAN without complex routing - so no chance of a 'lockup'.  Fortunately the Vigor 167 is probably the best VDSL2+ modem I've ever used, and are often cheap on eBay - I got mine second hand in perfect 'as new' condition for just £16.

I've just challenge the AI about this subnet conflict, and it has rethought it's answer -

You are correct — the dual-cable method with mismatched subnets (192.168.1.x on the Hub Two and 192.168.68.x on the Deco) is not reliable and can cause problems.

Putting two different IP subnets on the same Layer-2 network (the second Ethernet cable creates a shared broadcast domain) often leads to ARP confusion, intermittent connectivity, or routing conflicts. Some people make it work by giving a PC a secondary IP address in the 192.168.1.x range, but it is fragile and not recommended as a permanent solution. The PPPoE session itself is not directly affected (that runs on the bridged DSL side), but the management access becomes messy.

Reliable ways to access the Hub Two GUI after bridging

Here are the practical options, ranked from simplest/most reliable:

1. Temporary direct connection (most reliable, zero risk) Whenever you want to check DSL stats (sync speed, SNR, errors, etc.):

• Unplug any device from a free LAN port (1–3) on the Hub Two (or use a spare port).
• Plug a laptop or PC directly into that port with an Ethernet cable.
• On the laptop, set a temporary static IP:
  • IP address: e.g. 192.168.1.10
  • Subnet mask: 255.255.255.0
  • Gateway / DNS: leave blank
• Open a browser and go to http://192.168.1.254.
• When finished, set the laptop back to automatic (DHCP) and reconnect it to the Deco network.

This always works because you are talking directly to the Hub Two on its own subnet. No routing or dual-subnet issues.

2. Change the Hub Two’s management IP before enabling Bridge Mode (best for semi-permanent access) Do this before you turn on Bridge Mode:

1. Log into the Hub Two at http://192.168.1.254.
2. Go to Advanced Settings → My Network → IPv4 Configuration.
3. Change the Hub’s IP address to an unused address in the Deco’s LAN range. Deco defaults to 192.168.68.1, so a good choice is something like 192.168.68.254 (or whatever free address is outside the Deco’s DHCP pool).
4. Save. You will lose connection briefly — reconnect using the new IP.
5. Now enable Bridge Mode as normal.

After everything is running:

• Run a short second Ethernet cable from a free Hub Two LAN port to a free LAN port on the main Deco unit.
• Devices on the Deco network can now reach the Hub Two at the new IP (e.g. http://192.168.68.254) because both devices are on the same subnet via that cable.

This avoids the dual-subnet problem entirely.

3. Static route on the Deco (possible but model/firmware dependent) Some Deco models support static routes in the app (More → Advanced → Static Routing). You could try adding a route for 192.168.1.0/24 via the WAN interface, but success is inconsistent because the Hub Two’s management IP sits on the WAN side of the Deco and the Deco may not forward management traffic that way. The temporary direct method or the IP-change + second-cable method are more dependable.

Recommendation

For most people the temporary direct connection is the easiest and cleanest. You only need line stats occasionally, so plugging a laptop in for a couple of minutes is not a big inconvenience.

If you prefer always-on access without unplugging anything, change the Hub Two’s IP address to the Deco’s subnet before bridging, then add the second short cable. That combination is solid.