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Comment by diggan | Hacker News Reader

I looked into doing something similar for testing various ActivityPub implementations in various network sizes and conditions.

Turns out, I already had everything installed on my machine to do it, via `tc` (Explained a bit here: https://wiki.archlinux.org/title/advanced_traffic_control), which apparently came with the iproute2 package on my distribution.

With that, you'd be able to run something like this to add latency on a specific interface:

    tc qdisc add dev eth0 root netem delay 100ms

Really easy to use, works well in docker container too, comes with a bunch of different conditions you can apply (delay, packet loss, duplication) and you might just have it installed already.

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Yeah, tc/netem/tbf is amazing. I built a simple Python GUI over the top of it and ran it on a Pi in a touchscreen case - just a little black box with "Drop packets: [0%] [1%] [10%] [50%] / Corrupt packets: ..." etc. Clients were very impressed.

I'm actually quite surprised that a similar frontend doesn't seem to exist as a commercial hardware product, unless we missed one in our search.

You have a product here.

Yeah - I was looking around this week and think there is a “gap” for a good simple proxy - speed bump is nice but I am thinking just let my application do it’s thing, then let me replay certain traffic, that JSON needs to

I think a programmable proxy with simple hooks is what I want

The downside of tc is that it is kinda weird and tricky to get it to operate on incoming packets.

I had to write my own emulator once to simulate a specific commercial satellite terminal. The terminal had the behavior of queuing up packets until they hit a certain threshold or exceeded a time limit and then bursting them out in a big blob. It also "helpfully" reordered small packets to the front of the queue for better latency, which made TCP stacks very cross.

I thought tc only worked on outbound. How did you get it to work on inbound packets?

There is a way to do it by setting up another queue and redirecting inbound packets into that queue, but I don't remember the specifics. I do recall quite a bit of trouble getting it to work. If you search for it you should be able to find some topics on the subject.

The nice thing about speedbump is the ability to modulate the impairments. tc cannot do that.

That could be really useful for maybe simulating weather effects on satellite/RF over time?

tc can simulate various network issues: https://man7.org/linux/man-pages/man8/tc-netem.8.html

You could easily build something that could repeatedly call the tc command and feed it different levels of impairment. Doing so to simulate weather is a great idea. If you had a wave-rider buoy measuring wave height every half-second or so, you could even simulate the impairment of an RF connection over water due to waves.

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