erplibre/script/vpn/README.md

VPN — five open tunnels, secrets in a KeePassXC vault

vpn.py brings up, tears down and diagnoses a VPN tunnel. One driver per technology, five of them, all free software.

The split is the whole design: what is not secret (host, user, routes, MTU) lives in readable JSON configuration; the pre-shared keys and the passwords live in a KeePassXC .kdbx vault. A profile can therefore be shown, compared and shared without handing over the means to bring the tunnel up.

Which one to pick

Driver	Pick it when	Secrets in the vault
l2tp_ipsec	the far side imposes it: a router, a firewall, Windows RRAS	PSK + PPP password
wireguard	you control both ends — fastest, simplest	private key (+ optional PSK)
openvpn	the site handed you a .ovpn file	password, if the file needs one
openconnect	Cisco AnyConnect, Pulse, GlobalProtect, Fortinet appliances	password
sshuttle	all you have is SSH access — nothing to install on the far side	none: SSH keys do the work

Commands

./script/vpn/vpn.py check                          # ce que la machine sait faire
sudo bash script/install/install_vpn.sh wireguard  # ou : tous, sans argument
./script/vpn/vpn.py list
./script/vpn/vpn.py up       --profile acme --dry-run
./script/vpn/vpn.py up       --profile acme
./script/vpn/vpn.py status   --profile acme
./script/vpn/vpn.py diagnose --profile acme
./script/vpn/vpn.py down     --profile acme

Everything is also reachable from the CLI: TODO › Execute › Deployment › VPN, and from TODO › Execute › Network › VPN — a tunnel gets looked for in both places. The menu is where profiles are created and secrets are typed in; vpn.py is what the menu runs. Connecting from the menu shows the plan first and asks before running it.

Run it as yourself, not under sudo: the vault lives in your home and its master password is yours to type. Each privileged step calls sudo on its own, and --dry-run shows every one of them without running any.

Where things live

Path	Content
private/todo/todo_override_private.json	your profiles — gitignored, 0600
script/todo/todo.json	the vpn section, empty: profiles shared by a team can go here
your .kdbx vault	one entry per profile, ERPLibre VPN / <profile>
/dev/shm/erplibre-vpn/<profile>/	0700 root — the secrets, in tmpfs, erased on down
/run/erplibre-vpn/<profile>.*	non-secret state (chosen interface, pid, log), readable without sudo
/etc/ipsec.conf, /etc/ipsec.secrets	L2TP only: a marked block, removed on down

The three security rules

1. No secret in an argument. /proc/<pid>/cmdline is readable by every user of the machine. Secrets travel on standard input only; a single place (runner.py) holds that rule, and a unit test replays the plan of every driver and fails if a secret ever reaches a command line.
2. No secret on persistent storage. The files a technology insists on are written 0600 into tmpfs and erased on down. Two drivers need none at all: OpenConnect passes the password on standard input (--passwd-on-stdin), and sshuttle has no secret to begin with. One residual, stated rather than hidden: while an L2TP tunnel is up, root can read the pppd options file. pppd takes a password from a file or nothing.
3. The master password is written nowhere. Leave kdbx.password empty; it is asked once per session. Only the vault path is stored, in the single gitignored file. The CLI says so when it finds a master password in the configuration.

The L2TP PSK reaches strongSwan hex-encoded (PSK 0x…): same bytes, and no question of escaping a " or a \ inside a pre-shared key.

What each driver settles for you

L2TP/IPsec — three stages, and all three are needed for an interface: IPsec in transport mode protects UDP 1701, L2TP opens a session inside it, PPP authenticates. Six pitfalls are handled here, all six found by connecting to a real concentrator:

• charon { install_routes = no }, otherwise charon installs a route that captures the L2TP traffic — the classic "the SA is established, ppp0 never appears".
• An AppArmor rule. AppArmor confines charon by path and /dev/shm is not in its profile, so charon is denied the secrets file by the kernel and fails three stages later on "no shared key found" — with the PSK sitting there, correct. Only journalctl -k | grep DENIED says so. The rule goes in the local/ file Debian and Ubuntu provide for exactly this.
• rightid=%any. A gateway announces itself by its IP even when right is a name; without this, strongSwan refuses: "IDir '203.0.113.5' does not match to 'vpn.example.com'".
• A wait for the connection to load. ipsec start returns before the starter has pushed the connections; an immediate ipsec up fails on "no match" — on a perfectly valid configuration, the most misleading error of the sequence.
• The direction of authentication. require chap / require authentication (xl2tpd) and require-mschap-v2 (pppd) all mean require the PEER to authenticate to us. A client must not: the server refuses, and pppd tears the link down with "LCP terminated by peer (peer refused to authenticate)". What a client wants is refuse-pap and refuse-eap — which speak about us.
• A /32 survival route to the server (in all-traffic mode the ESP packets would enter the tunnel they carry), and resolvectl, because systemd-resolved ignores /etc/ppp/resolv.conf.

One packaging note that costs an hour if missed: without the openssl plugin (libstrongswan-standard-plugins), charon advertises 3DES, the concentrator picks it — often the only cipher it knows — and the negotiation dies on "ENCRYPTION_ALGORITHM 3DES_CBC not supported!". The installer ships it.

WireGuard — it has no session, so wg-quick up succeeds even with a wrong peer key or an unreachable endpoint. Nothing says no, because nobody is there to say it. This driver therefore waits for a handshake before calling the tunnel up. Routes come from AllowedIPs and belong to wg-quick; the driver does not double its work. No DNS = line either: wg-quick hands that to resolvconf, missing from many systemd-resolved installs, and the whole configuration fails when it is.

OpenVPN — it starts from the .ovpn the site gave you; this driver does not invent one. Two things that are not obvious: --cd, because a .ovpn references its neighbours relatively; and option order, because what follows --config overrides the file — a bare auth-user-pass inside would otherwise wait for a keystroke that never comes, the daemon being detached. Split tunnel is asked for with --route-nopull, which also drops the pushed DNS; the driver says so when it takes it.

OpenConnect — --non-inter is deliberate in password mode. Without it an unknown server certificate raises a question, and openconnect would read the answer from the standard input the password arrives on. With it, openconnect refuses at once and prints the --servercert sha256:… line to paste into the profile's oc_servercert. Routes belong to the server, through vpnc-script; the profile can add to them, not replace them.

Set oc_sso when the concentrator authenticates through a web form (SAML / SSO — Azure AD, Okta, Duo). There is then no password to send, and Cisco's own client needs a screen for its embedded WebKit browser — often with WEBKIT_DISABLE_DMABUF_RENDERER=1 for it to render at all; its CLI cannot do this flow. openconnect can, with no screen on the client machine: measured in its library, it listens on local port 29786 and waits for the browser's redirect after launching --external-browser with the login URL. On a server that "browser" is a plain echo, so the URL is printed for you to open in your own browser — bring the redirect back with

ssh -L 29786:localhost:29786 <the client machine>

before opening it. The password never leaves your own workstation. Both timeouts differ on purpose: two minutes for a password, five for a human walking through an identity provider.

sshuttle — no interface at all: it redirects through the firewall. Every interface and routing check is therefore silent for it, and the witness address is the only judge — this driver is the reason the probe field exists. It also insists on being run by you: it calls sudo itself, for the firewall only. Running it under sudo would open the SSH session as root, with root's keys.

Diagnosing

diagnose chains the checks and names the failing stage, lowest first, so that the first false line is the cause and not a consequence: what the kernel exposes · packages present · the technology's own check (IPsec SA, WireGuard handshake, daemon alive, OpenVPN initialisation) · interface and addresses · each declared route · the witness address that only answers through the tunnel · the last lines of the relevant journal. Set probe in the profile to an address reachable only through the tunnel — without it, "it works" stays an impression, and for sshuttle there is nothing else to go on.

The kernel stage catches a failure no configuration can fix. Upgrading the kernel package replaces /lib/modules/<version> with the new version's: the running kernel keeps the modules already loaded and can load no other. IPsec then becomes unavailable on a kernel that supports it, charon aborts at initialisation on a missing kernel-ipsec, and the symptom surfaces three stages higher as a connection never loaded. diagnose and up name the version whose modules are gone and offer the only remedy — a reboot. It is offered, never done: nothing is applied on a dry run, nor without a terminal to answer.

Adding a driver

drivers/base.py states the contract and carries everything true of all technologies: directory layout, state kept between processes, routes, systemd-resolved, the standard status checks. A new driver declares what is its own — packages, secrets, profile fields, the form the menu unrolls, the sequence up and down — and executes nothing: it asks a Runner, which either runs or merely shows. Registering it is one line in drivers/__init__.py, and test_vpn_drivers.py picks it up from the registry: the no-secret-on-a-command -line rule applies to it whether or not anyone thought about it.