When creating a tunnel using ethernet mode, the Mikrotik OpenVPN implementation refuses to work without an IPv4 address assigned to the TAP interface. Since this is a layer 2 tunnel, an address is not necessary.
It looks like just a sanity check, not something to do with the actual code. It would be nice if we could get some way to do without this, since it prevents the user to create a pure IPv6 tunnel*.
- I know, I know. The Mikrotik implementation doesn’t support IPv6. Hence the use of ethernet mode: we assign this to a local bridge, and assign the IPv6 to this bridge. It is not pretty, but gets the work done.