Commit https://github.com/vyos/vyos-1x/commit/b7d30137b17da49ed5099d4d96659b363fc7bcc9
calculated a "stable" synthetic MAC address per the interface. The problem is that this calculation is too stable.
Having Router1 and Router2 setup a connection both via tun10 interface will become the same "synthetic" MAC and this the same link-local IPv6 address. This breaks e.g. OSPFv3 badly.
As workaround one can:
```
set interfaces tunnel tun1337 address 'fe80::1:1337/64'
set interfaces tunnel tun1337 ipv6 address no-default-link-local
```