What is L4S?

[@LReBe7]

One important remark about L4S: as soon as one link along the data path bleaches the ECN bits (bit 14 and 15 of the IP header), you immediately lose the explicit congestion notification signal and you're back to boring old cubic. In fact, if you have certain traffic that you know is going to a certain destination that frequently bleaches ECN, you'll be better off configuring that traffic to go on some sort of random early dropping queue.

[@anjuksr2]

Excellent details