OSPFv2 through GRE link

[tbk49]

I need to run OSPF in a little scenario where I am using GRE over IPSec.

I am using FRR plugin and did a simple test by following the first example in the docs (https://docs.opnsense.org/manual/how-tos/dynamic_routing_ospf.html#setup-ospf-between-routers). The other device is not another OPNSense firewall. Yes, I also set the tunable as advised (https://docs.opnsense.org/manual/dynamic_routing.html) and I have set an interface firewall rule allowing ospf protocol traffic input on gre1 interface (I turned off the automatic firewall rule option per the referenced doc).

The problem is there is no communication from the firewall. To verify, I run tcpdump from the firewall cli to sniff the gre1 interface and I can only see the neighbor's hello packets. I am noticing a lot of warnings in FRR log file (Routing | Diagnostics | Log) such as the following:

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ospfd - interface gre1: 172.16.3.1: ospf_read network address is not same [172.16.3.2]
The GRE interface is on 172.16.3.0/30. The firewall is *.1 and neighbor *.2.