http://stevedischer.com/another-way-to-do-automatic-failover-with-mikrotik-routeros/
http://wiki.mikrotik.com/wiki/Two_gateways_failover
http://wiki.mikrotik.com/wiki/Failover_Scripting
http://wiki.mikrotik.com/wiki/Failover_via_Netwatch_III_%28English%29
http://wiki.mikrotik.com/wiki/Improved_Load_Balancing_over_Multiple_Gateways_Failover_Script