[IDEA] FFMUC Routed only with B.A.T.M.A.N. inside the local mesh

[awlx]

This is a draft idea how we could switch FFMUC to a routed approach without losing functionality of B.A.T.M.A.N. for local meshes.

Problem statement

We want to switch Freifunk Munich to a routed approach towards the gateways, because large layer2 domains pose too many problems. Also we want to get rid of the overhead of VXLAN and B.A.T.M.A.N. towards the gateways.

Idea

• Use wireguard to connect to the Freifunk Munich gateways

• Inside wireguard use a calculated link-local address which is derived from the public key

• v6

  • Run radvd on nodes which have an established wireguard tunnel to announce the v6 /64 inside the local network
  • the local /64 is assigned via wgkex
  • Default route via the wireguard tunnel

• v4

  • Use a fixed /20 per segment and set the next-hop to the v6 address of the gateway, also NAT on the node itself.
  • The node runs DHCP thus it becomes the default gateway for the local network. Also set B.A.T.M.A.N. GW Mode to server.
  • We need a transfer network between gateway and node

• Meshing

  • The node runs B.A.T.M.A.N. for local meshing just the same as on "normal" Gluon

• Why not babel?

  • We want to stay compatible to old nodes, which can just mesh like before.
  • A routing protocol is not needed in this approach, thus we avoid another failure domain.

What needs to be done?

• Test setup with that approach (two raspberry PIs or smth)
• Changes to gluon (dhcp-server, radvd, nat)
• wgkex needs to get a backend database from which transfer v4 addresses are picked
• wgkex also needs to have an database for v6 /64

Possible issues

• Kernel of OpenWRT is too old and doesn't support v6 next-hops for v4
• Meshing freaks out
• IP address conflicts while roaming

Known Issues

• No IPv4 Connectivity between clients which are not in the same local mesh
• Potential IPv4 collisions in spontaneous meshes

Glossar

• Nodes => Freifunk Router
• Gateway => Supernode

Discussion

https://chat.ffmuc.net/freifunk/channels/firmware

Comments welcome! 🚀