Maybe someone has some input on the following situation:
A RB5009 with 7.18.2 is connected to a 1000/1000 fiber modem directly in Spain and was working fast (at least 800/800) in the past.
Suddenly the connection speed dropped down to 50/50. I can reproduce this using Mikrotik BTEST, nPerf.com, iperf3, LibreSpeed, ftp transfer.
Now if I do an Ookla speedtest, either as Linux command line or via browser on their website, speed tops up to 920/900.
Any idea what might happen here?
If speedtest is fast, but nothing else is fast - your ISP is limiting you and setting an exception on speedtest 
Common practice in some areas
You are reading my mind They say they don’t. The graph that nPerf.com displays shows definitely that something is slowed down.
Any ideas how they detect it? I already tried port 8080 that Ookla is using.
Of course they are saying that.
Does your local telecommunication regulatory agency (probably Bundesnetzagentur - BNA) provide their own speed test application/portal? (In my country, also EU member, they do) If they do, test speed using their application/portal and if the results will be equally shitty, you’ll have grounds to file a complaint with BNA against your ISP.
Where are you testing your speeds to ?
Your problem could be that your Internet upstream provider ( or your upstream upstream providers feed(s) ) might have some saturated BGP feeds.
I would suggest performing multiple speedtests to many local and remote locations.
If speedstest(s) look good locally but not out on on the Internet to other countries , then I would suspect somebody somewhere is overbooking their saturated BGP networks.
I believe you might be in Spain , are all of the local speedtest servers in Spain reporting the same speeds.
How are your traceroutes to local and remote countries ? Where do the hops start slowing down ?
First, thanks for your input so far!
I am located at Moraira/Spain. The provider peers to Cogent3 at Valencia/Spain.
The line is rated 1000/1000 and in the past speed was around 900/900.
The fiber modem is directly connected to the RB5009. Because of DHCP the MTU is 1500.
Testing with Mikrotik Bandwidth Test against my Mikrotik router in Germany gives me around 50/50.
Testing from a Browser against:
https://www.movistar.es/test-de-velocidad/
https://librespeed.org
https://www.nperf.com
They all show me around 50/50.
Then I installed a VPS at Valencia and installed iperf3 and LibreSpeed on it.
Both show me around 50/50.
Then I ran Ookla Speedtest. Either the Ookla Linux command line speedtest or the public domain speedtest-cli or from a browser against https://www.speedtest.net give me speed above 800/800.
Here is the output of the “fast” speedtest:
root@srv-esp:~# speedtest -p
Speedtest by Ookla
Server: BIARTEL - Biar (id: 18815)
ISP: Closeness SL
Idle Latency: 9.54 ms (jitter: 0.76ms, low: 8.54ms, high: 10.38ms)
Download: 892.18 Mbps (data used: 908.0 MB)
25.06 ms (jitter: 1.70ms, low: 8.71ms, high: 34.87ms)
Upload: 861.63 Mbps (data used: 782.1 MB)
14.27 ms (jitter: 2.12ms, low: 8.65ms, high: 36.71ms)
Packet Loss: 0.0%
And the traceroute to the server used:
root@srv-esp:~# traceroute speedtest1.biartel.es
traceroute to speedtest1.biartel.es (78.41.80.11), 30 hops max, 60 byte packets
1 router-esp.esp (10.3.0.9) 0.202 ms 0.140 ms 0.162 ms
2 10.199.255.1 (10.199.255.1) 2.482 ms 2.403 ms 2.522 ms
3 10.254.254.1 (10.254.254.1) 6.460 ms 10.254.254.5 (10.254.254.5) 6.478 ms 6.463 ms
4 * * *
5 be8497.ccr31.vlc02.atlas.cogentco.com (154.54.39.173) 7.531 ms 7.220 ms 7.586 ms
6 wifiber.demarc.cogentco.com (149.14.4.202) 6.686 ms 6.629 ms 6.607 ms
7 5.180.229.111.core.valencia.spainwisp.com (5.180.229.111) 8.817 ms 9.274 ms 9.284 ms
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And this a traceroute to the “slow” LibreSpeed test server:
[admin@router-esp] /tool> traceroute 31.14.238.88
ADDRESS LOSS SENT LAST AVG BEST WORST STD-DEV STATUS
10.199.255.1 0% 4 2.8ms 2.7 1.9 3.5 0.6
10.254.254.5 0% 4 5.5ms 5.8 5.5 6.3 0.3
10.121.102.1 0% 4 14.3ms 14.5 14.3 14.7 0.2
100% 4 timeout
100% 4 timeout
100% 4 timeout
100% 4 timeout
185.111.185.45 0% 3 18.8ms 19.7 18.8 20.6 0.7
31.14.238.88 0% 3 18.8ms 19.9 18.8 20.8 0.8
Can you also test with https://www.fast.com (Netflix) and https://real-debrid.com/speedtest (multiple locations but download only)?
Oha, “fast.com” shows 480 Mbps (tested multiple times), “real-debrid.com” AMS: 42, RBX: 32, Cloudflare: 24.
It really looks like your ISP is “cheating” with well-known speed test services while throttling normal traffic (including to lesser-known test sites like Real-Debrid).
What if you use your browser to go to YouTube and watch a 4K video, while turning on the “Stats for nerds” in the context menu? Does Connection Speed shows values higher than 50000 Kbps?