I've had this issue myself when i was investigating DMVPN using OpenNHRP. It's a simple patch to remove the check / enforcement needed in bird, can't remember where now though since it was a while ago. When the check was removed i could set the interface to any type i wanted and i got ospf routing to work. No drawbacks detected during the testing. 2015-03-02 21:49 skrev Clint Armstrong:
I am trying to use BIRD to run OSPF inside a Phase 3 DMVPN using OpenNHRP. The problem I'm seeing is that it appears to be impossible to force type broadcast on a GRE interface. When I try, the message "Cannot use interface gre1 as broadcast, forcing nbma" is logged.
This may normally make sense, but the OpenNHRP daemon captures multicast traffic on it's interface and forwards it appropriately.
A configuration parameter to bypass this protection and allow broadcast on a GRE interface would be very helpful.