You are not logged in.
a reverse connection is pretty much anything when an outgoing connection from A to B is used in reverse as if B would had opened a connection to A
example: when you want to control a server you do this usually via SSH - you connect from your client via ssh to your server to control it remotely - but this very connection can also be re-used in reverse so B controls A - it's how botnets work: the client (infected bot pc) connects to a command and control server (often public IRC networks are abused) and waits for commands send from the admin to be executed
same would go in your situation: you have your private network unreachable from remote because of no static public ip and no dyndns (my question still remains: how do you find it then? is this what zerotier is for? if so: there's no difference in what I describe) - and a cheap public accessible server nearby
now your home network connects to the remote server from something cheap like a raspberry pi - or in your case thanks to openwrt: the router itself - and waits for some instructions for it - like: "please wake up my computer"
then from your remote location as you can't connect to your router directly as you don't know its current address (again: just use dyndns - there're so many out there - most router manufactures even provide reliable services which also should work in china behind the great big pooh firewall) you connect to the vps instead as you know its fixed public ip - and just let the open connection from your home relay back the command to WOL your computer - and you can re-use this already open link to tunnel ssh thru it
you also could - and I discourage everyone from using that method - please don't abuse public service - pay for your own! - use any public IRC - register two clients and a private channel - have your home network connect to it - and then use any IRC client to issue commands to it - and yes - this also can be abused to establish a working ssh connection
Offline
is this what zerotier is for?
Actually, yes.
I know the benefit for dynamic dns, and setup my own on the side of house A.
I think you could take a look at vpn services like Zerotier or Tailscale. They are not for well known method of anonymously accessing Internet services or bypassing some firewall, but of setting up one’s own private network across Internet. In my setup, 192.168.50.0/24 is my local lan subnet and 192.168.51.0/24 is my zerotier virtual network subnet. After setting up them you can access hosts from one location to another across Internet as if they are in the same lan.
And zerotier is free for personal use.
Offline