Is forwarding to port 9 (discard) essentially the same as blocking a port?

Question

My router (Linksys WRT1900ac) seems to leave port 4567 open, as discussed in this question. I'd like to block that port.

Unfortunately I see no easy way in the Linksys admin console to simply drop traffic from a specific port. However, it does allow port forwarding and triggering

I've learned that TCP port 9 is for the "discard protocol". If a host is listening on that port, it's supposed to discard the packets without comment.

If I forward traffic from port 4567 to port 9, am I in effect blocking the port? If something is listening on 9, the packets should be dropped without comment. And if nothing is listening on 9, I assume they'll just go into the bit-bucket on their own.

Update Using Twisty's tip in this post, I've confirmed that my DSL modem, not my router, is leaving the port open. The modem doesn't seem to forward this traffic to the router, so no action I take on the router will affect the fact that the port is open.

Answer 1

Pretty clever way of doing it, but anyway short answer, yes this would work as port 9 pretty much nullifies any data it receives.