Simulate bad network with pf

First create an anchor and reload pf conf:

(cat /etc/pf.conf && echo "dummynet-anchor \"lichess\"" && echo "anchor \"lichess\"") | sudo pfctl -f -

Pipe all traffic to port 9663 to dummynet:

echo "dummynet out quick proto tcp from any to any port 9663 pipe 1" | sudo pfctl -a lichess -f -

Configure the pipe:

sudo dnctl pipe 1 config bw 10Kbit/s plr 0.1 delay 500

Here it simulate a very bad network, with a limited bandwidth and a packet loss rate of 10%. This last command can be changed on the fly to test different network configurations.

Enable/disable firewall:

sudo pfctl [-e|-d]

Reset conf:

sudo dnctl flush
sudo pfctl -f /etc/pf.conf