GRE over IPSEC

[pongafence]

Hey all,

So firstly,  yes I did quickly try to search both the documentation and the forums for some quick answers,  but was left still wanting.

So at the moment,  I'm connecting a few sites together using IPSEC tunnels.  They're working fine.  However,  there is a new requirement now,  now that they're up.  To use a dynamic routing protocol over the tunnel.

I know that from the current IPSEC tunnel it's not possible.  But I know that with a GRE tunnel I can.

However,  configuring this in OPNsense isn't very clear cut,  or maybe it's that easy I'm over complicating it.

I'm able to establish the GRE tunnel.  But how do I encrypt it?

The reason for this,  is because I can't seem to use the OpenVPN option due to configuration limitations on the other end,  Mikrotik router and Cisco router.

Anyway,  how do I wrap it up?  Do I specify the IP addresses of the GRE tunnel?  Or do I specify the external IP's of each device in the IPSEC tunnels to wrap up the GRE tunnel?

Directions would be greatly appreciated.