I'm looking to create a backup link via cellular with a wAP LTE. The remote sites would have a standard internet connection (Cable, DSL, etc) with a tunnel (L2TP+ipsec probably, though EoIP+ipsec would be an option). The idea is to run OSPF+BFD on the main link and if it goes down, have an immediate re-route to the wAP LTE.
The question is, what is the lowest byte maintenance tunnel option?
I have 2 options for the backup link.
1) put the wAP LTE into OSPF as well. This will cost my maintenance bytes but they are small, probably livable.
2) don't have the LTE link in OSPF, just have a static route on each side at distance 240 so it's a circumstantial route when OSPF/BFD kills the primary path.
the basic question is, how many Mbits per month with EoIP, GRE, or L2TP eat up when 'idle'. I may or may not be able to get a static or even public IP address on the LTE link, but this doesn't really matter for the LTE because the tunnels will be 100% on the providers network (no open internet) and the data traversing the tunnel is already encrypted.