pfSense-On-A-Stick - 802.1Q Trunking With pfSense 2.0 RC1 and Mikrotik RouterBoard RB250G Smart Gigabit Switch with five ports and SwOS v1.5 - Stefcho's Tech Blog
IPsec - RouterOS - MikroTik Documentation
Basic L2TP/IPsec server configuration on a MikroTik device. – Netpro.lv