our net work is configured as given in the diagram
problem is in gateway of rb 1100
while the static ip customers of rb1100 who are reaching the host
having the mac address of the 450g ether2
Please explain better what your problem is.
Put your 2 ISP in rb100 and loadbalance as follow.
http://wiki.mikrotik.com/wiki/Improved_Load_Balancing_over_Multiple_Gateways