Remote Access

Accessing your home server from outside can be tricky. Please note that i am referring to accessing your home server from outside, not your home network. There is a big difference!

Access to the home server means access to your home services. You can, and should, remap using the reverse proxy any service which is not on the home server itself.

Access to the home network means get an IP on the home network and behave like your device is plugged-in the home network. This is not desirable because it will expose the devices really on the internal network to additional risks: what if your mobile device, while outside, is compromised? You just opened an unsecured route to access home….

If you need access to the home network, and please think twice because 99% it is not what you really need, you should use wireguard instead of the following approach.

You have a network interface of some kind between your home and your ISP provider. It could be a router or a gateway, it can be provided by the ISP or a device you bought and connected. This device acts as a firewall of kind and ensures that your home network is not accessible from outside.

In other words, unless you do specific actions, your home network will not be accessible from outside. Let's see what you could try.

If your ISP assign you a real IP address, then you can try to forward one or more ports so that those are reachable from outside.

To achive port forwarding, you need access to the network interface netween your home and your ISP (your gateway, or modem, or router…) and the option must be available.

Anyway the hopes that this will work today are really slim, because:

• Often ISPs will forbid it
• Having a real IP today is really uncommon, CG-NAT is instead the new default.

CG-NAT, or Carrier-Grade NAT, is today the de-facto standard for residential internet access. In other words, today having a public IP is basically impossible, unless you are a lucky american (where IP4 address pools where generously granted in the past to ISPs) or willing to pay a lot of money for a specific service. And even in this case, it might not be available.

If you are behind CG-NAT, port forwarding is moot and you have only two options left:

• Using a VPN service
• Using an external server as bridge

In both cases, you need a server located externally to your home, and that can be reached fro mthe internet, that you can use as an entry-point toward your home. The main difference is explained below.

There are providers out there called VPN providers, that will let your home network be hidden behind a fake exit point. You pay (and none will let you do tihs for free) and your home network connection toward the internet wll be masked by the VPN exit node. Some of them will also let you do port forwarding (again, usually, for an extra price).

You will still have a dynamic IP address, and this solution also raise additional privacy concerns since now all your traffic goes trough a third provider which might not even be in your own country and obey different laws.

A VPN by itself, even with port-forwarding, is not yet enough, you still need a way to get back into the home server from outside.

NOTE: when talking about VPN, do not confuse this with Wireguard, which is still a VPN technically, but it's intended to work on the other direction, to get back inside.

Any server on the internet with an IP address can be used to access your home server. So why not rent one, even the cheapest VPS (Virtual Private Server), and make it your home access point away from home? The advantages over using a VPN are:

• Usually cheaper (VPS can be rented for a fraction of the cost of a VPN)
• More scalable: you can always upgrade when you want to a better / more expensive service
• Can also be used as off-site backup storage if you purchase enough storage
• You are in full control, you can even install your favorite OS yourself, given your VPS allows it.
• The IP is static and will never change (with VPN, the exit node usually changes over time)

Some possible disadvantage:

• One more server to install & manage beside the home server

Of course, if you have the means, go for a phisical server which will guarantee you better privacy given that you will even rent the actual hardware. I do this, and it's about 20€ per month at the time of writing this page (2024).

Once you have extablished how you can make your home server visible on the internet, let's see how you can make so that you can access your services too. As i wrote at the beginning, the focus is on making your home services accessible, not your home network. This, again, is for security and protection. I assume all your services are already protected behinga reverse-proxy, even at home, that provides an HTTPS encrypted layer and a common SSO authentication (more on this here and here).

Unless you can have port-forwarding (but in this case you need to take care of Dynamic DNS for example), there are two ways to “get back in”. Both are ancrypted:

• Using Wireguard: you setup a wireguard server at home, then you need to install and configure clients on all the devices connecting from outside
• Using an SSH tunnel providing port-forwarding: this will allow any device to access your services, and no specific setup on them.

I choose the external server + SSH tunneling, because first of all i offer some public services, that would be impossible trough wireguard, and because i want to be able to access my services even if my devices are broken / unavailable at times. Is it secure? Yes, security is provided by the reverse-proxy + SSO, and privacy is guaranteed by using HTTPS on all services + encrypted SSH tunnels.

More over, if you can afford not one but two ISPs at home and two external services, you can also provide a pretty good level of redundancy, which is critical if you host important services for you and your family that should always be accessible. This is my case.

So, here are the assumption:

• You choose the “external server” + “SSH tunnel” solution
• You have two external servers: external-server1 and external-server2.
• You have two ISPs at home (see here for more details)

I will try with some ASCII art to illustrate:

        ┌───────────┐         
        │Home       │         
        │ ▲ Server ▲│         
        └─┼────────┼┘         
          │        │          
          │        │          
          │        │          
   ┌──────┼─┐    ┌─┼──────┐   
   │ISP 1 │ │    │I│P  2  │   
   └──────┼─┘    └─┼──────┘   
          │        │          
          │        │          
          │        │          
┌─────────┴┐      ┌┴─────────┐
│External  │      │External  │
│ Server 1 │      │ Server 2 │
│          │      │          │
│┌────────┐│      │┌────────┐│
││ SSH n.1││      ││ SSH n.2││
│└────────┘│      │└────────┘│
└──────────┘      └──────────┘

The home-server will port-forward to external-server1 via ISP 1 and, at the same time, to external-server2 via ISP 2.

If you have only one ISP or one external server, just ignore the other. Of course you can use any mix of two ISPs and one external server, or one ISP and two external servers as you like, each step is a bit less redoundant than the other of course.

This topic is better covered here.

This is my preferred method, mostly because: Advantages of SSH tunnels:

• Easy to setup
• Do not require any additional package on Linux (SSH is installed by default)
• Works in any settings, always
• Easily perform all kinds of port-forwarding natively and in both directions
• Allows to expose public services and web pages
• Allows access without any client configuration

Using SSH tunneling has one major drawback:

• The real “client” IP is always replaced by 127.0.0.1 on the home server at low-level (so not a HTTP level), making tools like Fail-to-Ban of little use.

OpenSSH is the default- SSH package installed in Gentoo. It creates a safe, encrypted tunnel between two hosts and it's based on OpenSSL. OpenSSH supports many useful features for your use case:

• Strong encryption of all exchanged data
• Host identification based on public&private keys
• User authentication based on public&private keys
• Strong password-less authentication with 2FA (certificate + password)
• Port forwarding from local to remote
• Port forwarding from remote to local
• TCP Keep-Alive support

To autmate and make SSH tunnels resillient to network disconnect or other failures, you need to install AutoSSH.

I have already stated above, but i will again state it here since it's very important. For SSH tunnel approach to be safe, you must:

• Use HTTPS on all your service. And i mean all.
• Use a reverse-proxy in front of all your services.
• Use strong authentication (proxy-auth, or Authelia or a similar services)

All these three points are covered by using NGINX reverse proxy + SSO as i describe in these pages.

One last time: HTTPS is mandatory.

You will create a specific user, called tunnel both on the local and the remote servers and allow the local user tunnel to login via private/public key exchange to the remote servers. This is always possible because the remote server is, by definition of internet, accessible from the home server.

The user tunnel will then activate a number of port-forwarding from the remote server to the local server, exposing directly only your home most-secured only services:

• Home SSH port: so you can access your home server from outside. This will be mapped to something different than 22 both for security reason and not to clash with the external server port 22.
• Home Reverse Proxy ports (80 & 443): so you can access all your secured services from outside.

Please note that you must expose port 80 of your reverse-proxy if you plan to use Let's Encrypt Certbot tool, or it will not work.

What you will need:

• Create a tunnel user on home server
• Create a tunnel user on remote server(s)
• Share home tunnel user public key to the remote server's tunnel user authorized keys
• Login from home to remote as user tunnel with appropriate options to create all the needed tunnels.

Everything will be properly encrypted and safe, and automated.

Create a new user called tunnel, but make sure it's home folder is on root partition because if, by any chance, your data partitions will not mount, you would lose the tunnels as well.

useradd -m tunnel

Create the SSH identity for the user tunnel:

su - tunnel
ssh-keygen

I suggest you do not setup a password for this key. It is slightly less secure, but you can always revoke the key if it gets leaked. If you setup a password, then you will need to provide it in the connection script, which kind of make it a mooth point anyway.

Your SSH public key will be stored under ~/.ssh/id_rsa.pub (this might change in newer SSH versions where RSA is phased out for better keys, YMMV).

Login to your remote server, create the user tunnel:

useradd -m tunnel

Copy / paste the home server user tunnel public key into the ~/.ssh/authorized_hosts file of the remote server tunnel user, as a new line. You should create the folder and the file if missing.

BE CAREFUL: you must set permissions properly for the .ssh folder and the authorized_keys file! They must not be accessible or readable by anybody but the user.

You might want to edit SSH daemon configuration and set in your server /etc/ssh/sshd_config:

ClientAliveInterval 10
ClientAliveCountMax 2

To ensure that on the remote server the user tunnel is allowed to create port-forwarding, add the following to your /etc/ssh/sshd.conf on the remote server:

Match User tunnel
        GatewayPorts clientspecified

and restart the SSHD service.

so that clients will be dropped and port freed automatically if they stop responding within 10 seconds for maximum two consecutive times.

Since you will need to redirect low-ports (<1024), and this is not possible with default SSH by design, you will need also the socat tool that allows you to create local redirections between the ports as needed. Emerge it:

emerge socat

Note: for security reasons, you might prefer to move the external server SSH port from the default 22 to some other value, like 222, in case you do so, remember to add -p 222 to your ssh and autossh command below.

Which kind of port-forwarding do you need? And how many?

SSH provides two kinds of port forwarding: remote-to-local and local-to-remote.

Remote to local: the specified port on remote server will be opened by SSH and any traffic trough that port will be redirected, encrypted and transparently, to a specific port (and possibly ip address) on the home server. This is useful to access a home service from outside.

Local to remote: the specified port on home server will be opened by SSH and any traffic will be redirected, encrypted and transparently, to a port of the remote server (and possibly also a specific IP address). This can be used to remap en external service on the local server, without giving an user direct access to the remote server.

You will mostly need the first one, of course.

The syntax is: -R<remote_ip>:<remote_port>:<local_ip>:<local_port>

• -R : specify it's a remote to local forwarding
• remote_ip: can always be 127.0.0.1, to use remote public IPs or 0.0.0.0 you need special configuration on remote server.
• remote_port: which port to listen to on remote server. Must be > 1024 (unprivileged)
• local_ip: destination IP for connection incoming from remote. Usually 127.0.0.1 but can be whatever you want
• local_port: destination port for connections. It's your exported service port.

A good idea is to forward home server SSH port to some custom port on the remote server, so that you can access your home via SSH. From your home server, as tunnel user run:

ssh tunnel@external-server1 -R0.0.0.0:2022:127.0.0.1:22

will allow you to SSH on port 2022 of the remote server, and actually login to your home server SSH. Try that now, from the home server, as any user from a new terminal, run:

ssh myuser@external-server1 -p 2022

and you will login as user myuser… on your home server!

Note: remember to login once manually, as user tunnel, to ensure remote host keys are accepted of your tunnels will fail.

Note: running SSH with port forwarding like i showed you above is ok, but will not reconnect automatically in case the tunnels fails nor will survive a reboot. A better approach is discussed down below, for now, you can test your connections with SSH.

So, assuming the prerequisites are satisfied, you have all your home services behind a reverse-proxy protected with HTTPS and Let's Encrypt real certificates, all you need to do it actually forward the HTTP(80) and HTTPS(443) services from your home to your remote server. Yes, also port 80 must be forwarded for Let's Encrypt automatic certificate renewal to work.

There is a catch that you need to be aware of: SSH is not capable (by design, and because of security) to forward ports below 1024. Unfortunately ports 80 (HTTP) and 443 (HTTPS) are both below 1024. The solution to this issue is to let SSH forward those ports only on the external server 127.0.0.1 (non-public) network on higher ports (8080 instead of 80 and 8443 instead of 443) and then add a second internal forwarding on the remote server from port 127.0.0.1:8080 to 0.0.0.0:80 and from port 127.0.0.1:8443 to 0.0.0.0:443. (Check note below, you might need 8443 local as well if using my reverse proxy setup)

Due to this limitation, the command, to be run from the home server looks like:

ssh tunnel@external-server1 -R0.0.0.0:2022:127.0.0.1:22 -R127.0.0.1:8080:127.0.0.1:80 -R127.0.0.1:8443:127.0.0.1:8443 

The SSH rule (port 2022/22) it has been already discussed above.

Note: my reverse proxy guide will use port 8443 for external connections to differentiate from internal connections. This is why the above rule forwards to home server port 8443 instead of port 443.

At this point you need to add the two internal redirections from 80 → 127.0.0.18080 and 443 → 127.0.0.1:8443 on the remote server using socat. Create the redirect start file under /etc/local.d/01-redirect.start:

01-redirect.start

#!/bin/bash
(socat TCP-LISTEN:443,fork,reuseaddr TCP:127.0.0.1:8443)&
(socat TCP-LISTEN:80,fork,reuseaddr TCP:127.0.0.1:8080)&

make it executable and manually start it, as root, for this first time (it will autostart next reboot):

chmod +x /etc/local.d/01-redirect.start
/etc/local.d/01-redirect.start

At this point, you should be able to reach your home services from your external server.

There is a simple and pretty solid tool, AutoSSH, that will help you pack it all up and make is more resilient with autoreconnection capabilties. Autossh will start SSH for you and restart it when it fails. but there are some caveats as autossh will exit and might end up quitting in some special cases, like if the remote server is not reachable at boot or the network connection gives up for a prolonged period of time. To ensure this does not happen, you need to set AUTOSSH_GATETIME=0.

First of all, install autossh:

emerge autossh

Now create the following start-up script in /home/tunnel/tunnels.sh:

tunnels.sh

#!/bin/bash 
export AUTOSSH_GATETIME=0

function run_tunnel()
{       
        while true
        do
                autossh -M 0 \
                        -nNT -q \
                        -o ServerAliveInterval=30 \
                        -o ServerAliveCountMax=2 \
                        -o ExitOnForwardFailure=yes \
                        -R0.0.0.0:5022:127.0.0.1:22 \
                        -R127.0.0.1:8080:127.0.0.1:80 \
                        -R127.0.0.1:8443:127.0.0.1:8443 \
                        $1
                sleep 30
        done
}

run_tunnel <<ip address of external-server1>>&
tun_tunnel <<ip address of external-server2>>&
wait

Note: remeber to add your external servers SSH port if you changed it from the default 22! (-p newport).

Note: as you can see I used port 8443 also locally due to reverse proxy setup! Check here for more details. Local 443 is without authentication, while local 8443 has reverse proxy with enabled.

You need to set AUTOSSH_GATETIME as stated above, and for additional safety i have also wrapped those tunnels with a while loop, and notice that due to this reason i am not using the -f option for SSH or AutoSSH. You might never be carefull enough when it comes to losing remote access to your server, and maybe you are traveling abroad.

Also, for additional resillience, you might want to use the real ip address instead of external-server1&2 so that is DNS fails but network is working, the tunnels will connect anyway.

To start it on boot, drop this init script to /etc/init.d/tunnel: create /etc/local.d/99-tunnels.start:

99-tunnels.start

#!/bin/bash
start-stop-daemon -b -m -p /var/run/tunnel.pid -n tunnel -u tunnel /home/tunnel/tunnels.sh

and make it executable.