François' Blog

Taming WireGuard in eduVPN

Published on 2021-02-23

WireGuard is a new, relatively simple VPN technology implemented the “right way”. This means, no shortcuts were taken by the developers. Keep it simple was the motto and they were not afraid to do some plumbing. Two examples of this were integrating WireGuard directly in the Linux kernel whilst also updating the kernel’s cryptography stack. The other was writing wintun to make tun devices perform and work well on Windows as a replacement for OpenVPN’s TAP driver.

The “keep it simple” approach is very much appreciated. Nobody wants a bloated VPN solution, as many of those exist already. This leaves some work when wanting to integrate WireGuard in “enterprise” solutions. It is unacceptable to require someone to download the WireGuard client and copy paste a configuration file before being able to connect to the office VPN. So we’ll need to make this better.

We are trying to make WireGuard a “drop-in” replacement for OpenVPN where both can be supported at the same time. We’ll probably keep OpenVPN around for a while until we can solve the lack of VPN-over-TCP support in WireGuard. This feature is especially helpful when trying to connect from broken networks that either block UDP traffic, have trouble with MTUs or block all ports except a few common ones. With OpenVPN we can solve all these problems by having the client connect over for example tcp/443.

Luckily, the eduVPN software already has two parts which can help a lot when integrating WireGuard:

  1. Server with OAuth API to configure VPN clients;
  2. Client applications for all major platforms.

Currently, only OpenVPN is available in eduVPN, but leveraging the OAuth API that exists between server and client, integrating WireGuard is not so difficult anymore. However, for WireGuard we need to implement a number of things that are not necessary with OpenVPN.

Two major differences between OpenVPN and WireGuard are:

  1. WireGuard does not allow for a “hook” to be implemented when a VPN client “connects”, even the entire notion of “connecting” is not as clear-cut when talking only about UDP;
  2. There is no IP management, i.e. WireGuard does not control and manage the pool of issued IP addresses to clients.

The former is a problem when you want to implement (fine grained) authorization. For example in eduVPN the concept of profiles allows issuing IPs from a certain IP range depending on group membership as determined in the identity management system of the organization.

The latter is a problem when you want to make efficient use of IP addresses, either because you integrate in big networks where you can’t simply allocate a /16 block for your VPN clients, or when using public IPv4 addresses for your VPN clients. Public IPv4 address space has been depleted for a while now.

Technically it is not really complicated to implement this using WireGuard, but it requires turning the way of configuring around. Instead of implementing a hook to determine who has access to a “profile”, in this scenario we just provision WireGuard with the right public keys of the allowed clients and we’ll use the eduVPN application to “claim” and “release” IP addresses before and after connecting to the VPN. Integrating this tightly with the eduVPN application allows for transparent operation without the user having to do anything different when the underlying VPN technology is WireGuard.

Building this is exactly what Nick Aquina did during his internship at SURF. Modifications were made to the server, and the eduVPN Android application was modified to use the new WireGuard API calls. The proof of concept works and shows that our ideas work in practice. All details of the work can be found in Nick’s thesis.

Some work remains, but it is getting closer and something we look forward to make available before the end of the year.

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