WAN throughput degradation after terminating PPPoE with RB2011UAS

You should configure a VLAN and PPPoE client on a PC/Mac

I don’t have a PC, and I when I configure PPPoE on a Mac, I keep getting No route to host errors. Setting the VLAN ID is not straightforward on a Mac, and when I configure that via a virtual interface, I can’t configure the PPPoE service on that interface. Networking on Macs is a mess, I know, and I also suspect that it’s a tangent (see below).

As mentioned at the beginning of this thread, if I terminate PPPoE with Unifi, I get the full 920Mbps speed consistently. The problem with that setup is that PPPoE drops frequently, and even when it doesn’t drop out, I get sporadic 100% packet loss which makes the connection unreliable. Fast, but unreliable.

When I terminate PPPoE with Mikrotik, I get highly variable throughput in iperf3, but otherwise a really stable PPPoE connection, which is essential to me.

Interestingly, when I use speedtest instead of iperf3, I get much better throughput: https://www.speedtest.net/result/12254379428

This makes me wonder if iperf3 default TCP mode behaves in a way that makes RB2011UAS throughput inconsistent. Running in UDP mode confirms this theory:

root@linux-host:~# iperf3 -c w.gerhard.io -u -b 0
Connecting to host w.gerhard.io, port 5201
[  5] local 192.168.1.11 port 57866 connected to 176.58.103.232 port 5201
[ ID] Interval           Transfer     Bitrate         Total Datagrams
[  5]   0.00-1.00   sec   114 MBytes   955 Mbits/sec  83570
[  5]   1.00-2.00   sec   114 MBytes   953 Mbits/sec  83450
[  5]   2.00-3.00   sec   114 MBytes   953 Mbits/sec  83450
[  5]   3.00-4.00   sec   114 MBytes   953 Mbits/sec  83440
[  5]   4.00-5.00   sec   114 MBytes   953 Mbits/sec  83450
[  5]   5.00-6.00   sec   114 MBytes   953 Mbits/sec  83450
[  5]   6.00-7.00   sec   114 MBytes   953 Mbits/sec  83450
[  5]   7.00-8.00   sec   114 MBytes   953 Mbits/sec  83450
[  5]   8.00-9.00   sec   114 MBytes   953 Mbits/sec  83450
[  5]   9.00-10.00  sec   114 MBytes   953 Mbits/sec  83440
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Jitter    Lost/Total Datagrams
[  5]   0.00-10.00  sec  1.11 GBytes   953 Mbits/sec  0.000 ms  0/834600 (0%)  sender
[  5]   0.00-10.06  sec   895 MBytes   746 Mbits/sec  0.023 ms  172511/829707 (21%)  receiver

So I am able to achieve 953Mbit/s with UDP in the following network setup:

|- w.gerhard.io (2.5Gbps) - public iperf3 server
|
GPON ONT (syncs at 1Gbps, symmetric)
|
|- MikroTik RB2011UAS (1Gbps) - acting as PPPoE client
  |
  |- Unifi DreamMachine Pro (1Gbps)
    |
    |- Linux host (1Gbps)

What could make the RB2011UAS under-perform when using TCP instead of UDP?

I am suspecting that it’s the +9 years old CPU which clocks at 600Mhz, but considering that this maxes out at 23% when running the benchmark, I’m suspecting that it’s something else, but I’m not sure what exactly. I am wondering if this would solve my problem: https://forum.mikrotik.com/viewtopic.php?t=179868