What ports do client agents listen on?

Coming from https://www.nomadproject.io/docs/install/production/requirements#ports-used, I see 2 ports are required for client agents but it doesn’t explicitly say if it’s ingress or egress. I first guessed clients wouldn’t need ports to listen on, and instead they would establish a long-lived connection to the server for all communication. Why would clients even need an open port instead of talking via an open connection with the server in a reverse tunnel-ish style?