I have two Ubuntu server-based routers and I'd like to bond (in broadcast mode, since I only care about redundancy) a radio link (where the radio equipment is connected to an Ethernet port) and a LTE channel (that uses a mPCIe modem) upon which a GRE tunnel is put.
I've read the documentation and configured netplan to use NetworkManager as renderer, and I've tried to create the bond using nmcli. It seems that I cannot add the tunnel as slave in the bonding (when setting 'type' to 'ip-tunnel' nmcli complains about a 'mode argument required"), so I've added it with type "ethernet". However, when I try to bring the slave up I get:
# nmcli con add type ethernet ifname wccp0 master bond0
Connection 'bond-slave-wccp0' (xxxxxxxxxxxxxxxxxxxxxxxx) successfully added.
# nmcli con up bond-slave-wccp0
Error: Connection activation failed: No suitable device found for this connection.
Unfortunately, due to some routing policies out of my control, I cannot get rid of the tunnel.
How can I set up such an interface bonding?