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Bufferbloat is a flaw found in many routers. Bufferbloat causes considerably increased latency and network slowdown when there is other traffic on your network that uses the router.

Third-party router firmware such as the latest version of OpenWrt LEDE (vers 17.01.5) is supposed to fix the bufferbloat issue.

However, using OpenWrt LEDE 17.01.5 on a BT Home Hub 5 type A router, I find that I am still suffering from some bufferbloat, as measured by the DSL Reports Speed Test, which gives me low score on the bufferbloat measurement (a D to F score typically).

Interestingly my bufferbloat is much worse on upload compared to download: my normal ping time is around 8 ms, and this goes up to about 50 mg during the download phase on the DSL Reports test, but goes up to around 600 ms during the upload phase.

In terms of the quality score, DSL Reports gives me an A or B typically. But my bufferbloat score is low, so clearly the bufferbloat issue is still present.

Does anyone have any suggestions as to why I am still getting some bufferbloat, when the OpenWrt LEDE firmware is designed to fix the bufferbloat problem?

When I was using the BT Home Hub 5 with standard firmware, the bufferbloat problem was even worse, with latency going up to 2000 ms during upload. So installing OpenWrt LEDE has made an improvement, but has not entirely fixed the problem.

I am connected to my ISP by ASDL2+, using PPPoA with LLC encapsulation. I have a fast (by ASDL standards) download speed of around 18.5 Mbps, due to being very close to my telephone exchange, and upload speed of around 1 Mbps. I use the Plusnet ISP in the UK.

Ash90
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  • *"why I am still getting some bufferbloat, when the OpenWrt LEDE firmware is designed to fix the bufferbloat problem?"* -- You only updated the firmware of just one device in the network. That one device is not the sole culprit in network buffering. – sawdust Sep 20 '18 at 00:39
  • When I perform the DSL Reports test, no other devices are connected to my LAN, only the router and my Mac desktop computer. It could in principle be a bufferbloat problem in the Mac, but I've ruled out that possibility by observing ping times on the Mac while some uploads and downloads are being performed on another computer (an Android tablet) through the router's WiFi: ping times also shoot up in this scenario, indicating the bufferbloat issue is in the router and not in the Mac. – Ash90 Sep 20 '18 at 01:54
  • *"When I perform the DSL Reports test, no other devices are connected to my LAN"* -- You're poorly informed as how that test is performed. There is a remote server (which is located OUTSIDE your ISP in amazon and google data centers), a DSLAM, and who-knows-what-else on the other end of your DSL connection. – sawdust Sep 20 '18 at 02:27
  • So you are saying that the bufferbloat problem is likely upstream from the router in my home, and is probably located at the local telephone exchange or in the ISP. Certainly reading this webpage www.dslreports.com/comments/2905 about my ISP Plusnet suggests it may be prone to bufferbloat. – Ash90 Sep 20 '18 at 02:39
  • *"So you are saying that the bufferbloat problem ... is probably located at the local telephone exchange or in the ISP."* -- No, you're doing a poor job comprehending what's written. FYI the comment about the servers being *"located OUTSIDE your ISP in amazon and google data centers"* is not a guess, but an actual quote from http://www.dslreports.com/speedtest – sawdust Sep 20 '18 at 04:50
  • Note that the answer to this problem was hinted at by forum member Spiff: it seems that the Smart Queue Management (SQM) software, which combats bufferbloat, was not installed on my OpenWrt/LEDE router. Installing and configuring it using the instructions given here https://openwrt.org/docs/guide-user/network/traffic-shaping/sqm fixed the issue: I then got A scores for both bufferbloat and quality (packet loss) on the DSL Reports test. – Ash90 Sep 21 '18 at 13:38

1 Answers1

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It's probably one of two things, maybe both:

  1. Although OpenWrt/LEDE contain the fq_codel network scheduler that combats bufferbloat, it's possible you didn't enable it. Go verify that you're using fq_codel as your network scheduler.
  2. Even if you're using fq_codel so your OpenWrt/LEDE router doesn't experience bloat, bloat may be building up on other devices on your network, such as your broadband modem or other routers, gateways, or Wi-Fi APs. The good news is, if you enable HTB traffic shaping to make your OpenWrt router a slight bottleneck for all traffic going into or out of your network, it can use fq_codel to fight bufferbloat before bloat can build up on any other devices on your network. So enable that as well.

Also, look into cake/sqm-scripts; it's included in recent versions of OpenWrt/LEDE, and it's the latest way to make sure you're set up to battle bufferbloat in the most efficient manner.

Spiff
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    Thank you so much Spiff, it seems that Smart Queue Management (SQM) which implements fq_codel to combat bufferbloat was not installed on my router (I bought the router on eBay with OpenWrt/LEDE preinstalled). So I installed SQM using the instructions given here: https://openwrt.org/docs/guide-user/network/traffic-shaping/sqm and once configured, I started getting A scores for both bufferbloat and quality (packet loss) on the DSL Reports test, and occasionally even A+ scores. So this solved my problem. Many thanks for pointing me in the right direction. – Ash90 Sep 20 '18 at 15:14