Protocol suggestion!

[khurram49]

Hello Techies,

I need your help/suggestion which protocol is best suited for the attached topology.

I have 2 ISP connection. Primary internet connection is ISP1 and 2nd is for failover.

Scenario 1: If primary internet goes down traffic automatically shift on secondary WAN.

Scenario2: If any Router (R4, R5) goes down traffic disperse on both side.  

[MHM Cisco World]

the R2 connect to two other router R1 & R3 via fastether Link, 
fastether have a broadcast capability and OSPF by default for this type of link set network broadcast
BUT
here there is only two router connect to this broadcast, so we can change the network to be point-to-point.
in my lab I do 
show ip ospf interface brief 
before set network 
and after set network  

[khurram49]

R1 & R6 are routers connected with the switch and rest of all are Layer 3 switches. These devices are connected with Fiber cable. 

[MHM Cisco World]

can you new draw topology and mention that this R and this l3 sw.

also if there any l2 sw please mention where.

[khurram49]

[MHM Cisco World]

the RED Yellow and Blue Circle are the BROADCAST domain connect multi L3SW or Router.
My idea is to push the DR to be any Router not doing NAT to Internet which is R2 and R3 
the DR BDR election depend on interface priority and you can config the priority via 
ip ospf priority X <<-X as show in photo
also for Yellow circle since there are only two L3SW connect via BROADCAST network we can change the network type to Point-to-Point 

NOTE:- config the priority BEFORE run router ospf process because the DR/BDR election can not consider new router add high priority router in election.