How to forward port by ssh

There are 3 machine

1. My machine
2. Host A with public IP
3. Target Host B with can be reached from Host A

The goal is that I and my friends want to access target host B services in convenience. We can ssh to Host A with public IP.

Local Forwarding

Run this command on my machine

ssh -L 123:targetB:80 userA@hostA

• We can access targetB:80 by myMachine:123 instead
• The traffic will be forward from myMachine:123 through ssh tunnel to hostA and the forward to targetB finally.

Remote Forwarding

Run this command on hostA

ssh -R 123:targetB:80 me@myMachine

• We can access targetB:80 by myMachine:123 instead
• It's similar to local forwarding but the ssh tunnel is created by hostA which is the forwarder
  
• The traffic will be forward from myMachine:123 through ssh tunnel to hostA and the forward to targetB finally.

Dynamic Forwarding

Run this command on my machine

ssh -D 123 userA@hostA

• It's similar to local forwarding but it doesn't specify the target:port because the target address and the port will be determined automatically by application protocol such as SOCKS.
• We can access targetB:80 by SOCKS proxy in browser or OS network settings.
  
• Currently SOCKS4 and SOCKS5 protocols are supported.

Remarks

• There might have firewall issues. It might have to change some port unless the packets will be blocked.
• This method is for TCP traffic. For UDP, you may have to try other methods.