Set up OpenConnect VPN Server (ocserv) on Ubuntu 16.04/17.10 with Let’s Encrypt

Installing OpenConnect VPN Server on Ubuntu 16.04/17.10

sudo apt install ocserv

Installing Let’s Encrypt Client (Certbot) on Ubuntu 16.04/17.10 Server

sudo apt install ocserv
sudo apt install software-properties-common
sudo add-apt-repository ppa:certbot/certbot
sudo apt update
sudo apt install certbot

Obtaining a TLS Certificate from Let’s Encrypt

certbot certonly --standalone -d ocserv.example.com

Editing OpenConnect VPN Server Configuration File

sudo nano /etc/ocserv/ocserv.conf
auth = "plain[/etc/ocserv/ocpasswd]"
tcp-port = 443
udp-port = 443
run-as-user = nobody
run-as-group = daemon
socket-file = /var/run/ocserv-socket
server-cert = /etc/letsencrypt/live/ocserv.ml/fullchain.pem
server-key = /etc/letsencrypt/live/ocserv.ml/privkey.pem
ca-cert = /etc/letsencrypt/live/ocserv.ml/chain.pem
max-clients = 8
max-same-clients = 0
try-mtu-discovery = true
device = vpns
dns = 8.8.8.8
dns = 8.8.4.4
cisco-client-compat = true
default-domain = ocserv.example.com
tunnel-all-dns = true

Then comment out all the route directives (add # symbol at the beginning of the following four lines), which will set the server as the default gateway for the clients.

route = 10.10.10.0/255.255.255.0
route = 192.168.0.0/255.255.0.0
route = fef4:db8:1000:1001::/64

no-route = 192.168.5.0/255.255.255.0

Fixing DTLS Handshake Failure

DTLS handshake failed: Resource temporarily unavailable, try again.
sudo cp /lib/systemd/system/ocserv.service /etc/systemd/system/ocserv.service
sudo nano /etc/systemd/system/ocserv.service

Comment out the following two lines.

Requires=ocserv.socket

Also=ocserv.socket
sudo systemctl daemon-reload
sudo systemctl stop ocserv.socket
sudo systemctl disable ocserv.socket
sudo systemctl restart ocserv.service

Creating VPN Accounts

sudo ocpasswd -c /etc/ocserv/ocpasswd username

Enable IP Forwarding

sudo nano /etc/sysctl.conf
net.ipv4.ip_forward = 1
sudo sysctl -p

Configure Firewall for IP Masquerading

ifconfig
sudo iptables -t nat -A POSTROUTING -o ens3 -j MASQUERADE

Preserving Iptables Rules

apt-get install iptables-persistent

If apt-get install iptables-persistent has no effect, run dpkg-reconfigure iptables-persistent instead

Or do it manually :
By default, iptables ruls are lost after reboot. To preserve them, you can switch to root user and then save your rules to a file.

su -

iptables-save > /etc/iptables.rules
nano /etc/systemd/system/iptables-restore.service
[Unit]
Description=Packet Filtering Framework
Before=network-pre.target
Wants=network-pre.target

[Service]
Type=oneshot
ExecStart=/sbin/iptables-restore /etc/iptables.rules
ExecReload=/sbin/iptables-restore /etc/iptables.rules
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target
sudo systemctl daemon-reload

sudo systemctl enable iptables-restore

Install and Use OpenConnect VPN client on Ubuntu 16.04/17.10 Desktop

sudo apt install openconnect
sudo openconnect -b vpn.example.com:port-number

-b flag will make it run in the background after connection is established

sudo pkill openconnect
sudo apt install network-manager-openconnect network-manager-openconnect-gnome

References
https://www.linuxbabe.com/ubuntu/openconnect-vpn-server-ocserv-ubuntu-16-04-17-10-lets-encrypt
https://yoursunny.com/t/2017/ocserv-letsencrypt/
https://lowendbox.com/blog/install-openconnect-server-on-ubuntu-16-04/
https://www.digitalocean.com/community/tutorials/how-to-list-and-delete-iptables-firewall-rules

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