Bonding is a technology that allows aggregation of multiple ethernet-like interfaces into a single virtual link, thus getting higher data rates and providing failover.
###Router-1
/interface bonding
add name=bonding1 slaves=ether9,ether10
/ip address
add address=172.16.1.1/24 interface=bonding1 network=172.16.1.0
###Router-2
/interface bonding
add name=bonding1 slaves=ether9,ether10
/ip address
add address=172.16.1.2/24 interface=bonding1 network=172.16.1.0