Yggdrasil builds a multi-hop IPv6 overlay network using peer-to-peer connections. You can string a whole bunch of nodes together using whatever means (cables, wireless or TCP peerings over the internet or any other network) and you get a full-mesh network where everyone can reach everyone else.

It's designed to be as minimal-configuration as possible and scalable in a way that many other mesh routing protocols aren't.

How does it compare to Zerotier? They seem to be in the same market

Quite different. ZT is centralized config, direct peer to peer, automatic key exchange, virtual switch.

YG is decentralized, direct peer to peer and multi hop routing, manual key exchange for direct peering, virtual internet (each node is a router to another nodes)

ZT (and Tailscale) requires a central node coordinator for automatic config and peer key exchanges, peers directly to each node to create a flat virtual network, not multi hop routing, between two peers you need a reachable IP or port mapping (supports UPNP) by one of them (fixed in config there are private TCP relays when carrier NAT/double NAT/ restrictive firewalls are in place, very slow), Uses UDP for the links, mimics a virtual switch and support custom IPV4 / IPV6, good for virtual private networks.

YG (and CJDNS) is kinda an overlay public network, is fully decentralized, it supports automatic routing between nodes to mimic a virtual Internet, each node is a router too, needs to register each key for every direct peer node connection (config needs peer key, reachable ip and port, but supports automatic key exchange for local networks), YG uses TCP for the links, support self-healing routing, every peer has an IPV6 address derived by its public key.

ZT (and Tailscale) can mimic a mesh network and node routing because supports bridge nodes between networks (routing between virtual switches), but is not self-healing and somewhat heavy work to config. ZT is fully open source, can be config with your own node coordinator and discovery helpers (Controllers and Moons in ZT), not easy. Only Taislcale client is open source, can't be config with your own node coordinators for free.

You can mix ZT and YG, weird side effects warranted but works. (Edited post - some grammar fixes)

So it's a kind of VPN?

It's an overlay network (a software defined network that runs on top of another network... like you internet service providers network).

It's closer to bittorent than a VPN. It has end-to-end encryption and each node (the app that runs on your PC) distributes routes to each other (similar to how routing works on the Internet between large networks). It appears to be a flat spanning-tree style network.

They mention that it is using similar code and ideas as the cjdns project.

This page [1] has answered most of the questions I has on the project.

[1] https://yggdrasil-network.github.io/about.html

Do I understand correctly that it does not do hole-punching, and e.g. unlike with a VPN a host behind NAT will not be able to accept incoming connections?

This is correct in the sense of peering, however hosts behind a NAT can simply connect to any other host on the network such as a pubic peer and then they can accept incoming connections over the yggdrasil network.

I use yggdrasil for NAT hole punching my VPN, for example.

can it be a bit compared to what tailscale does for ipv4 ?

I haven't used tailscale so... I think so? Tailscale is pretty light on the details, and even their docs say that they have been reluctant to describe how it works.

>People often ask us for an overview of how Tailscale works. We’ve been putting off answering that, because we kept changing it!

Yggdrasil is fully peer to peer and doesn't require a central coordinator like tailscale does. Ygg is closer to a global network than a private one. You can make a private network, but if any peers on the network peer to the global net then your whole network is now peered. this should be handled at the firewall level, or with an overlay VPN.

No, it's a kind of virtual public network.

So not a kind of VPN, but a kind of VPN? :)

The "P" in VPN usually stands for "Private", not "Public".

I think that was the joke.

You joke, but unfortunately this was the poor wording that GNUnet chose to use. https://docs.gnunet.org/handbook/gnunet.html#First-steps-_00...

I still facepalm whenever I think about this.

A mesh VPN, or kinda a mesh TOR really.