Port Forwarding for L2TP/IPSec VPN Behind Verizon Actiontec MI424WR-GEN2 Rev. E v20.21.0.2 - Verizon
That's interesting, because none of the built-in (predefined) IPSec or L2TP 'services' (read: Port Forwarding Rules) had GRE enabled. (see last screenshot in my post). However, I can add GRE to the new 'service' I defined in Advanced > Port Forwarding Rul...