Portmaster throttles LAN bandwidth

[ashetl]

What happened:

When running Portmaster on Kubuntu 24.10, my connection speeds to devices on LAN are throttled by over 10x (as shown in the iperf3 results below).

Here are iperf3 results to the same device on my LAN. Other than the reported network speed, the only difference between them is that Portmaster was running on the iperf3 client machine for the first one and was disabled on the iperf3 client machine for the second one.

[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.00 sec 640 KBytes 5.24 Mbits/sec 0 81.5 KBytes
[ 5] 1.00-2.00 sec 384 KBytes 3.15 Mbits/sec 0 104 KBytes
[ 5] 2.00-3.00 sec 640 KBytes 5.24 Mbits/sec 0 128 KBytes
[ 5] 3.00-4.00 sec 512 KBytes 4.19 Mbits/sec 0 151 KBytes
[ 5] 4.00-5.00 sec 512 KBytes 4.20 Mbits/sec 0 174 KBytes
[ 5] 5.00-6.00 sec 512 KBytes 4.19 Mbits/sec 0 197 KBytes
[ 5] 6.00-7.00 sec 640 KBytes 5.24 Mbits/sec 0 219 KBytes
[ 5] 7.00-8.00 sec 640 KBytes 5.24 Mbits/sec 0 261 KBytes
[ 5] 8.00-9.00 sec 384 KBytes 3.15 Mbits/sec 0 339 KBytes
[ 5] 9.00-10.00 sec 512 KBytes 4.19 Mbits/sec 0 427 KBytes

---

[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.00 sec 5.25 MBytes 4.40 Mbits/sec 0 sender
[ 5] 0.00-10.84 sec 4.81 MBytes 3.72 Mbits/sec receiver

[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.00 sec 5.12 MBytes 42.9 Mbits/sec 2 126 KBytes
[ 5] 1.00-2.00 sec 5.62 MBytes 47.2 Mbits/sec 1 151 KBytes
[ 5] 2.00-3.00 sec 5.50 MBytes 46.1 Mbits/sec 1 171 KBytes
[ 5] 3.00-4.00 sec 5.62 MBytes 47.2 Mbits/sec 0 192 KBytes
[ 5] 4.00-5.00 sec 5.38 MBytes 45.1 Mbits/sec 0 210 KBytes
[ 5] 5.00-6.00 sec 5.12 MBytes 43.0 Mbits/sec 1 224 KBytes
[ 5] 6.00-7.00 sec 6.00 MBytes 50.3 Mbits/sec 1 239 KBytes
[ 5] 7.00-8.00 sec 5.62 MBytes 47.2 Mbits/sec 0 253 KBytes
[ 5] 8.00-9.00 sec 6.25 MBytes 52.4 Mbits/sec 0 269 KBytes
[ 5] 9.00-10.00 sec 6.00 MBytes 50.3 Mbits/sec 0 283 KBytes

---

[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.00 sec 56.2 MBytes 47.2 Mbits/sec 6 sender
[ 5] 0.00-10.03 sec 55.6 MBytes 46.5 Mbits/sec receiver

The issue is not confined to iperf3 traffic. I experience the same for file transfers by SSH between the same devices. I used iperf3 merely to demonstrate the differences.

I am not using SPN.

What did you expect to happen?:

Since Portmaster is not blocking the traffic on the relevant ports, I expected Portmaster to have no impact on LAN network speed.

How did you reproduce it?:

On my system (Kubuntu 24.10), I experience the same each time I have Portmaster running vs each time I do not have Portmaster running.

Debug Information:

Portmaster reports no blocked connections relevant to the above iperf3 tests, but if it would help to see logs, please let me know which ones.

[github-actions]

Greetings and welcome to our community! As this is the first issue you opened here, we wanted to share some useful infos with you:

• 🗣️ Our community on Discord is super helpful and active. We also have an AI-enabled support bot that knows Portmaster well and can give you immediate help.
• 📖 The Wiki answers all common questions and has many important details. If you can't find an answer there, let us know, so we can add anything that's missing.

[ashetl]

After further research, I believe the severity of the throttling is related to Tailscale. I understand that there is no plan to make Portmaster compatible with Tailscale.

Here are iperf3 results conducted on LAN between the same two devices as above but with Tailscale disabled on both. Once again, Portmaster is running for the first test and disabled for the second.

While less severe, there is still a material difference between the results.

[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.00 sec 2.62 MBytes 22.0 Mbits/sec 0 140 KBytes
[ 5] 1.00-2.00 sec 2.00 MBytes 16.8 Mbits/sec 0 158 KBytes
[ 5] 2.00-3.00 sec 2.38 MBytes 19.9 Mbits/sec 0 167 KBytes
[ 5] 3.00-4.00 sec 4.00 MBytes 33.5 Mbits/sec 0 170 KBytes
[ 5] 4.00-5.00 sec 4.00 MBytes 33.6 Mbits/sec 0 141 KBytes
[ 5] 5.00-6.00 sec 3.00 MBytes 25.2 Mbits/sec 0 117 KBytes
[ 5] 6.00-7.00 sec 3.00 MBytes 25.2 Mbits/sec 0 136 KBytes
[ 5] 7.00-8.00 sec 4.25 MBytes 35.6 Mbits/sec 0 156 KBytes
[ 5] 8.00-9.00 sec 3.50 MBytes 29.4 Mbits/sec 6 130 KBytes
[ 5] 9.00-10.00 sec 4.75 MBytes 39.8 Mbits/sec 1 154 KBytes

---

[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.00 sec 33.5 MBytes 28.1 Mbits/sec 7 sender
[ 5] 0.00-10.01 sec 32.9 MBytes 27.6 Mbits/sec receiver

[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.00 sec 6.38 MBytes 53.4 Mbits/sec 1 194 KBytes
[ 5] 1.00-2.00 sec 5.25 MBytes 44.0 Mbits/sec 0 214 KBytes
[ 5] 2.00-3.00 sec 4.88 MBytes 40.9 Mbits/sec 1 229 KBytes
[ 5] 3.00-4.00 sec 6.38 MBytes 53.5 Mbits/sec 1 247 KBytes
[ 5] 4.00-5.00 sec 5.88 MBytes 49.2 Mbits/sec 0 189 KBytes
[ 5] 5.00-6.00 sec 5.88 MBytes 49.3 Mbits/sec 0 226 KBytes
[ 5] 6.00-7.00 sec 5.88 MBytes 49.3 Mbits/sec 0 246 KBytes
[ 5] 7.00-8.00 sec 5.38 MBytes 45.0 Mbits/sec 0 181 KBytes
[ 5] 8.00-9.00 sec 4.62 MBytes 38.8 Mbits/sec 0 147 KBytes
[ 5] 9.00-10.00 sec 4.50 MBytes 37.7 Mbits/sec 0 122 KBytes

---

[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.00 sec 55.0 MBytes 46.1 Mbits/sec 3 sender
[ 5] 0.00-10.05 sec 53.8 MBytes 44.9 Mbits/sec receiver