R5;
enable
config t
hostname R5
int s1/1
ip add 192.168.56.1 255.255.255.0
no shutdown
exit
int s1/2
ip add 192.168.57.1 255.255.255.0
no shutdown
exit
router ospf 100
network 192.168.57.0 0.0.0.255 area 0
network 192.168.56.0 0.0.0.255 area 0
end

R6:

enable
config t
hostname R6
int s1/0
ip add 192.168.56.2 255.255.255.0
no shutdown
exit
int s1/2
ip add 192.168.67.1 255.255.255.0
no shutdown
exit
router ospf 100
network 192.168.56.0 0.0.0.255 area 0
network 192.168.67.0 0.0.0.255 area 0
end

R7

enable
config t
hostname R7
int s1/4
ip add 192.168.57.2 255.255.255.0
no shutdown
exit
int s1/5
ip add 192.168.67.2 255.255.255.0
no shutdown
exit
router ospf 100
network 192.168.57.0 0.0.0.255 area 0
network 192.168.67.0 0.0.0.255 area 0
end