Digital Ocean is offering a private LAN for internal communication between the VMs, and they claim it’s isolated from other customers. You get some random addresses within 10.133.0.0/16 (or maybe some other range), and they can talk to each other on dedicated virtual NICs.
But that’s it. You cannot run OSPF because multicast packets are not let through. Even if you manage configuring direct neighbors in OSPF, it renders useless because the private LAN does not allow packets with destination IP addresses outside of the LAN range. So, any kind of routing with next hop in the private LAN would not work.
Too bad guys, very disappointed. So, we need to resort to Tinc VPN for internal routing, and this private LAN doesn’t make any sense.