How to allow SSH connections from LAN and WAN on different ports


Is it possible to configure SSH to listen for connections on both internal and external interfaces, using different ports? Jack Wallen says “yes.”

Data Security system Shield Protection Verification

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I want to pose a situation: Say you have users on your internal LAN who need to connect to your servers via SSH, but you also have users on your external WAN who need to do the same. Do you just open up SSH on port 22 and be done with it? Or do you worry that leaving port 22 open on the external side of things might invite attacks?

What if you could open up port 22 for the LAN and port 2222 for the WAN? You can, and I’m going to show you how.

SEE: Windows 10 security: A guide for business leaders (TechRepublic Premium)

What you’ll need

In order to make this work, you’ll need a server that accepts SSH connections and the ability to manipulate the traffic. I’ll be demonstrating on a Ubuntu Server 18.04 instance, which works with Uncomplicated Firewall (UFW). If you are working with a server that doesn’t make use of UFW, you’ll have to modify your firewall rules according to the tool used on your Linux distribution. Also, if you have a network security device that controls the traffic from the LAN and/or WAN, you’ll have to make adjustments there as well–how that is done will depend upon the platform in use.

The machine running SSH will also need to have two network cards, one configured for LAN usage and one configured for WAN usage. For the sake of example, we’ll call those ens5 (LAN) and enp1s0 (WAN). 

How to configure SSH

The first thing to be done is the configuration of SSH. This is actually quite simple. Open the necessary configuration file with the command:

sudo nano /etc/ssh/sshd_config

In that file (Figure A), uncomment the Port 22 line and add a Port 2222 line.

Figure A

sshportsa.jpg

The sshd_config file allowing both ports.

Once you’ve made those changes, save and…



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