Reverse SSH tunneling with iptables config for SMTP local developing

smtp_port_forwarding.md

Setup NAT routing (server)

• Setup redirecting 25 port to 2525 port for ens3 interface

iptables -t nat -A PREROUTING -i ens3 -p tcp --dport 25 -j REDIRECT --to-port 2525

• Show config sudo iptables -t nat -L -n -v
• Save config sudo iptables-save

Setup SSH server (server)

• https://superuser.com/a/591963

Note that if you use OpenSSH sshd server, the server's GatewayPorts option needs to be enabled (set to yes or clientspecified) for this to work (check file /etc/ssh/sshd_config on the server).

• https://askubuntu.com/a/50075

echo "GatewayPorts clientspecified" >> /etc/ssh/sshd_config
service ssh restart

[OPTIONAL] Setup SSH connection without password auth (local)

• Gen sertificate files; if ~/.ssh/id_rsa and ~/.ssh/id_rsa.pub already exist – use them

ssh-keygen -t rsa -b 16384
ssh-copy-id [-p 22] user@server

[OPTIONAL] Setup SSH alias for connection (local)

• Edit SSH client config nano ~/.ssh/config:

Host *
  ServerAliveInterval 60
  UseKeychain yes

Host HostAliasName
  Hostname 123.123.123.123
  Port 22
  User username
  Compression yes
  PasswordAuthentication no

Create SSH tunnel (local)

• Run with bind_address ssh -R :2525:localhost:2525 -N HostAliasName

Enjoy!

$ telnet fuck.xyz 25
Trying 123.123.123.123...
Connected to fuck.xyz.
Escape character is '^]'.
220 Come to daddy