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393 lines
8.9 KiB
393 lines
8.9 KiB
Title: Bypassing ISP Blocked Ports |
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Date: 2021-04-10 |
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Category: Writing |
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Summary: Bypass ISP blocked ports using VPN port forwarding for public access. |
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Wide: true |
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Short: 2 |
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[TOC] |
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My residential ISP blocks inbound traffic to common ports like 22, 80, and 443. |
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I use an OpenVPN tunnel to forward these ports so that I can self-host a |
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public media server. It does __not__ require users to be on the VPN. |
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This article explains how I set it up and is targeted towards Linux sysadmins. |
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## Overview |
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I have a cheap $5 per month virtual server with [Digital |
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Ocean](https://digitalocean.com) that runs Debian GNU/Linux 10. An OpenVPN |
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server is running on this virtual server. |
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My media server at home has an OpenVPN client connected to the server and is |
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assigned a static IP on the VPN network. |
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The virtual server has routing enabled and forwards inbound traffic __from the |
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internet__ to my media server at home. This allows me to have external HTTP and SSH |
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access. |
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## Server Setup |
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Spin up a Debian 10 virtual server on your favourite hosting provider and set |
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your user up as you would normally. You should probably harden this server. |
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Assign a subdomain to it like `vpn.example.com`. |
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Install the following requirements: |
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``` |
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$ sudo apt update |
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$ sudo apt install openvpn ufw |
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``` |
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### OpenVPN Server |
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These steps roughly follow [this |
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guide](https://wiki.debian.org/OpenVPN#TLS-enabled_VPN). |
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Generate TLS certificates and keys: |
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``` |
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$ cd /etc/openvpn |
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$ sudo openvpn --genkey --secret static.key |
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$ sudo make-cadir easy-rsa/ |
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$ sudo chown -R tanner:tanner easy-rsa/ |
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``` |
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Replace `tanner` with your Linux username, this is temporary. |
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<span class="aside">The `.rnd` file prevents a warning</span> |
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``` |
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$ cd easy-rsa/ |
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$ ./easyrsa init-pki |
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$ head /dev/urandom > pki/.rnd |
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$ ./easyrsa build-ca |
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``` |
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Enter a password you won't forget in case you want to add another client later. |
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The Common Name you choose is not important. |
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Generate Diffie–Hellman params: |
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``` |
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$ ./easyrsa gen-dh |
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``` |
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Generate a server cert: |
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``` |
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$ ./easyrsa build-server-full server nopass |
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``` |
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Generate a client cert: |
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``` |
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$ ./easyrsa build-client-full mediaserver nopass |
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``` |
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We make a `mediaserver` client because we want to assign a static IP to it. You |
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need to make a different one for each client you want with a static IP. |
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Also, if you want generic clients that all get dynamic IPs for use on your |
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laptop, phone, etc. to protect you from public WiFi (like a normal VPN), create only a single extra one: |
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``` |
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$ ./easyrsa build-client-full client nopass # optional |
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``` |
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Leave off `nopass` if you want to password protect the config file keys when you |
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set up a new client. |
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Create the server config file `/etc/openvpn/server.conf`: |
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<span class="aside">Can't use port 443 here since it'll be forwarded</span> |
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``` |
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port 1194 |
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proto udp |
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dev tun |
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topology subnet |
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ca /etc/openvpn/easy-rsa/pki/ca.crt |
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cert /etc/openvpn/easy-rsa/pki/issued/server.crt |
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key /etc/openvpn/easy-rsa/pki/private/server.key |
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dh /etc/openvpn/easy-rsa/pki/dh.pem |
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tls-auth /etc/openvpn/static.key 0 |
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client-config-dir /etc/openvpn/ccd |
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server 10.8.0.0 255.255.255.0 |
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client-to-client |
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duplicate-cn |
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keepalive 10 120 |
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cipher AES-256-GCM |
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auth SHA256 |
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comp-lzo |
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max-clients 10 |
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user nobody |
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group nogroup |
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persist-key |
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persist-tun |
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``` |
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Assign a static IP + chmod: |
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``` |
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$ cd /etc/openvpn |
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$ sudo chown -R root:root easy-rsa/ |
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$ sudo mkdir ccd |
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$ sudo touch ccd/mediaserver |
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``` |
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Replace `mediaserver` with whatever client name you used above. Edit it like so: |
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<span class="aside">Your home server will be `10.8.0.100`</span> |
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``` |
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ifconfig-push 10.8.0.100 255.255.255.0 |
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``` |
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Test your config by running: |
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``` |
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$ sudo openvpn --config /etc/openvpn/server.conf |
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``` |
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If you run `ip addr` in another terminal, you should see an entry like this: |
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``` |
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5: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> stuff |
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link/none |
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inet 10.8.0.1/24 brd 10.8.0.255 scope global tun0 |
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valid_lft forever preferred_lft forever |
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inet6 fe80::d9fc:b2f9:34e6:5ed2/64 scope link stable-privacy |
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valid_lft forever preferred_lft forever |
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``` |
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### systemd |
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If it works fine, persist OpenVPN with systemd: |
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``` |
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$ sudo systemctl enable openvpn@server |
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$ sudo systemctl start openvpn@server |
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$ sudo systemctl daemon-reload |
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$ sudo service openvpn restart |
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``` |
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Test it works by rebooting: |
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``` |
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$ sudo reboot |
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$ ssh vpn.example.com |
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$ ip addr |
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``` |
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### Port Forwarding |
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I use `ufw` to handle the iptables rules because I use it anyway as a firewall |
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when I harden my servers. |
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Enable routing: |
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``` |
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$ sudo sysctl net.ipv4.ip_forward=1 |
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``` |
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Edit `/etc/sysctl.conf` to set: |
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``` |
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net.ipv4.ip_forward=1 |
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``` |
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Edit `/etc/default/ufw` to set: |
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``` |
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DEFAULT_FORWARD_POLICY="ACCEPT" |
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``` |
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Add this to the top of `/etc/ufw/before.rules`: |
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``` |
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*nat |
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:POSTROUTING ACCEPT [0:0] |
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# ssh port forwarding |
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-A PREROUTING -d 123.123.123.123 -p tcp --dport 2222 -j DNAT --to-dest 10.8.0.100:2222 |
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-A POSTROUTING -d 10.8.0.100 -p tcp --dport 2222 -j SNAT --to-source 10.8.0.1 |
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# Allow traffic from OpenVPN client to eth0 |
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-A POSTROUTING -s 10.8.0.0/8 -o eth0 -j MASQUERADE |
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COMMIT |
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``` |
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Replace `123.123.123.123` with your VPN server's external IP address and `eth0` |
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with the external interface. |
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This will forward TCP traffic on port 2222 to your home server. If you want to use |
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port 22, then you need to set the VPN SSH server to something else. |
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A full example of `/etc/ufw/before.rules` with other ports included can be found |
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here: |
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[https://txt.t0.vc/URUG](https://txt.t0.vc/URUG) |
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Apply the changes to `ufw`: |
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``` |
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$ sudo ufw disable && sudo ufw enable |
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``` |
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## Client Setup |
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Switch to your home server or client machine. |
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Install OpenVPN: |
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``` |
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$ sudo apt update |
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$ sudo apt install openvpn |
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``` |
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### Client Configs |
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For static IP clients (like your home server), create the config file `/etc/openvpn/client.conf`: |
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``` |
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client |
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dev tun |
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proto udp |
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remote vpn.example.com 1194 |
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resolv-retry infinite |
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nobind |
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persist-key |
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persist-tun |
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remote-cert-tls server |
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cipher AES-256-GCM |
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auth SHA256 |
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comp-lzo |
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key-direction 1 |
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<ca> |
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[server /etc/openvpn/easy-rsa/pki/ca.crt] |
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</ca> |
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<cert> |
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[server /etc/openvpn/easy-rsa/pki/issued/mediaserver.crt] |
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</cert> |
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<key> |
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[server /etc/openvpn/easy-rsa/pki/private/mediaserver.key] |
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</key> |
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<tls-auth> |
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[server /etc/openvpn/static.key] |
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</tls-auth> |
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``` |
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Replace the `[server ...]` lines with the contents of that file on the __VPN |
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server__, for example: |
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``` |
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$ sudo cat /etc/openvpn/easy-rsa/pki/ca.crt |
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---> copy & paste result |
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``` |
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Also replace `vpn.example.com` with the subdomain you assigned earlier. |
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For device clients (like your laptop and phone), create the config file `client.ovpn`: |
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<span class="aside">`redirect-gateway def1` forces traffic over the VPN</span> |
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``` |
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client |
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dev tun |
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proto udp |
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remote vpn.example.com 1194 |
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redirect-gateway def1 |
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resolv-retry infinite |
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nobind |
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persist-key |
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persist-tun |
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remote-cert-tls server |
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cipher AES-256-GCM |
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auth SHA256 |
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comp-lzo |
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key-direction 1 |
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<ca> |
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[server /etc/openvpn/easy-rsa/pki/ca.crt] |
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</ca> |
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<cert> |
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[server /etc/openvpn/easy-rsa/pki/issued/client.crt] |
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</cert> |
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<key> |
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[server /etc/openvpn/easy-rsa/pki/private/client.key] |
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</key> |
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<tls-auth> |
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[server /etc/openvpn/static.key] |
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</tls-auth> |
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``` |
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The `client.ovpn` file is ready to be imported into your VPN clients. |
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Test your config by running: |
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``` |
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$ sudo openvpn --config /etc/openvpn/client.conf |
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``` |
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If you run `ip addr` in another terminal, you should see an entry like this: |
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``` |
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7: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> stuff |
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link/none |
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inet 10.8.0.100/24 brd 10.8.0.255 scope global tun0 |
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valid_lft forever preferred_lft forever |
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inet6 fe80::b2:ed71:6c98:4bc9/64 scope link stable-privacy |
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valid_lft forever preferred_lft forever |
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``` |
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Try pinging the server: |
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``` |
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$ ping 10.8.0.1 |
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PING 10.8.0.1 (10.8.0.1) 56(84) bytes of data. |
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64 bytes from 10.8.0.1: icmp_seq=1 ttl=64 time=71.5 ms |
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64 bytes from 10.8.0.1: icmp_seq=2 ttl=64 time=73.0 ms |
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... etc |
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``` |
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### systemd |
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If it works fine, persist OpenVPN with systemd: |
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``` |
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$ sudo chown root:root /etc/openvpn/client.conf |
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$ sudo chmod 600 /etc/openvpn/client.conf |
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$ sudo systemctl enable openvpn@client |
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$ sudo systemctl start openvpn@client |
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$ sudo systemctl daemon-reload |
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$ sudo service openvpn restart |
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``` |
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### Client Apps |
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On Android I use "OpenVPN for Android" and on Linux I use the |
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`network-manager-openvpn-gnome` Debian package. |
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To add your VPN on Gnome, open VPN settings, import file, and select |
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`client.ovpn`. If the private key is missing, select it from |
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`~/.cert/nm-openvpn/`. |
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## Closing Thoughts |
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You should now be fine to access your home server from over the internet. |
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To forward additional ports, just edit the `/etc/ufw/before.rules` file like |
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above and apply the changes to `ufw`. |
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You can now point a domain to your virtual server's IP and use that to connect |
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to your home server. Use a CNAME to make it easy to change later: |
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``` |
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NAME TYPE VALUE |
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-------------------------------------------------- |
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vpn.example.com. A 123.123.123.123 |
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myserver.example.com. CNAME vpn.example.com. |
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``` |
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Finally, make sure any server programs are listening / bound to `10.8.0.100` or |
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`0.0.0.0` so that they can get traffic from that interface.
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