kernel: conntrack: generic helper won’t handle protocol 47.
UPDATE 06/2023 The nf_conntrack_proto_gre is now a built-in module in kernel >= 5.1 and it is not possible to build it as a separate module. You can check if the module is built into the running kernel using the following command: grep CONFIG_NF_CT_PROTO_GRE /boot/config-$(uname -r) Output of above: (this means the module is built into […]