Complicated network application
A security gateway can simultaneously serve as an LAC and an LNS. Additionally, it can support more than one incoming call. If memory and physical lines are enough, L2TP can receive and make multiple calls at the same time. For such a complicated network, you can see through the previous configuration examples and consider them comprehensively to find a configuration solution.
Pay attention to static route configuration. Many L2TP applications rely on static routes to initiate connection requests.