During my efforts to establish an L2TP VPN on our MikroTik RouterOS I poured over countless guides and tutorials. So when I finally had a working VPN what did I do? Wrote my own guide of course! This guide uses the WebFig interface, but the principles apply to WinBox as well.

The biggest problem I faced during this configuration was the Phase2 IPsec Policy Proposal. After identifying this as the roadblock I used trial and error to identify a policy that worked with High Sierra’s L2TP over IPsec VPN interface. This is not to say that this is the only configuration that will work, but this is the one that I found to work with system I had available for testing.

It may be useful to use L2TP just as any other tunneling protocol with or without encryption. The L2TP standard says that the most secure way to encrypt data is using L2TP over IPsec (Note that it is the default mode for Microsoft L2TP client) as all L2TP control and data packets for a particular tunnel appear as homogeneous UDP/IP data packets to the IPsec system. 

Multilink PPP (MP) is supported in order to provide MRRU (the ability to transmit full-sized 1500 and larger packets) and bridging over PPP links (using Bridge Control Protocol (BCP) that allows sending raw Ethernet frames over PPP links). This way it is possible to setup bridging without EoIP. The bridge should either have an administratively set MAC address or an Ethernet-like interface in it, as PPP links do not have MAC addresses.