Ssh – How to forward multiple ports in the SSH configuration with LocalForward

That's a tricky thing to get done. Your best bet is to use some SOCKS redirector like socksify or redsocks, but none will give you what a VPN can, so you'd better set it up. VPN allows you to connect even whole networks, forward your traffic through secure channels, make your computers all appear as in one LAN and so on.

You can use OpenVPN to do that - there's a pretty good documentation on it's site, though it might require some knowledge about networking to decide what and how you want.

However, if you don't wish to use it, but want to stay with SSH instead - you may refer to SSH-BASED VIRTUAL PRIVATE NETWORKS section of man ssh or https://help.ubuntu.com/community/SSH_VPN, which describes the topic pretty well.

Not the most elegant way, but here's how I would do it:

• Replace the port specifications in your original file with a unique pattern. For example:

  LocalForward myport localhost:myport
  

• Alias ssh from within your .bashrc:

  alias ssh='/path/to/ssh_wrapper.pl'
  

• Write the file /path/to/ssh_wrapper.pl:

  #!/usr/bin/perl
  
  use strict;
  use warnings;
  my $cmdline = join ' ',@ARGV;
  if($cmdline =~ / -p\s*([0-9]+)\b/ and $cmdline=~ / -N/){
       my $port = $1;
       system("sed 's/myport/$port/g' /etc/ssh/ssh_config > /tmp/ssh_config");       
  }
  else{
       system("sed 's/LocalForward/#LocalForward/' /etc/ssh/ssh_config > /tmp/ssh_config");
  }
  $cmdline .= ' -F /tmp/ssh_config';
  my $pid = fork;
  $pid ? wait : exec("/usr/bin/ssh $cmdline");
  unlink '/tmp/ssh_config';
  

  Basically, this will parse your ssh command line and if it finds a -p option followed by a numeric port specification, it will create a new ssh_config in /tmp/ssh_config by substituting every occurrence of myport with the numeric port value you specify on the command line. After that, it fork-execs a system call to the real ssh with your command line. If it created its own configuration file, It adds a -F option to your command line to ensure ssh reads from the newly-created configuration file instead. Finally, the parent process waits for the ssh fork to finish, after which it removes the temporary ssh configuration file.

Disclaimer

This code is untested. Try at your own risk. Back up your configuration file first!

Edit

The code as previously written, will break with a "Bad port specification" error when you don't supply a numeric port via -p so I added code to comment the LocalForward part out in case it's not needed. I also made sure that the substitution in the config file won't occur unless there's also a -N option because you might want to specify a port via -p without requiring forwarding (e.g. to ssh into a box that uses a non-standard port).