Dear members,
I’m having hard times trying to configure DHCP server/relay over GRE tunnel due to the fact that i cannot select tunnel interface when creating the DHCP server. I’m running the latest stable version and i would like to guide me for an workaround or a cold stone NO answer.
Is it something doable or i need to change the solution ? 
For direct connection to DHCP server, you need to use an L2 tunnel, i.e. EoIP or VPLS (the latter may not be possible in your network scenario as it requires an end-to-end MPLS network). DHCP is designed to work on L2 interfaces. GRE is an L3 point-to-point interface.
The “relay via GRE” way should be possible, but I hazily remember I’ve discussed that with Mikrotik support some years ago and the DHCP server was answering through the interface to which it was attached, which would exclude the GRE too. But I was doing that with policy-based IPsec, not with GRE, so there may be some subtle difference.
Thanks for your reply sindy, much appreciated!
I have some deployments using EoIP option for centralized DHCP solution but i am encoutering some strânge traffic issues due to mixed interface members în bridge (with vlan filtering). Most likely mtu has something to do with this, but i couldn’t prove it.
I will try to reproduce your scenario using my VMs before going to live deployment.
Thanks again and if no one will come up with a smarter work around în 48 hours i will Mark your answer as The solution for my situation for further references.
Best regards,
Andrei