rconn: creating generic reverse connections

by do son · July 14, 2021

rconn (r[everse] conn[ection]) is a multiplatform program for creating reverse connections. It lets you consume behind NAT and/or firewall services without adding firewall rules or port-forwarding. This is achieved by creating a connection from the node behind the firewall/NAT to a port on your local machine, and then a port is exposed in your machine through which you can connect to the service that is behind the firewall/NAT. All traffic is routed through the initial connection that was opened by the machine behind the firewall/NAT.

Explanation

Say your IP address is 11.11.11.11, and you’ve got machine 22.22.22.22 behind firewall/NAT and you want to connect to it via RDP. First, you’d have to make sure your RDP server is running, normally on 3389. Now the problem is you can’t connect to 3389 from outside because of NAT or firewall. Then in your local machine, you’d have to run this: rconn -s 1111 2222 And in the machine behind firewall/NAT you’d have to run this: rconn -c 11.11.11.11 1111 127.0.0.1 3389 Now you can connect to your own port 2222 with an RDP client, this will effectively be the same as connecting to 22.22.22.22:3389.

Usually, most firewalls allow all outbound traffic, but if this is not the case, you can try 80 or 443 instead of 1111.