Not a problem dear

C:\>tracert 10.0.0.10 Tracing route to 10.0.0.10 over a maximum of 30 hops: 1 0 ms 0 ms 0 ms 172.16.20.1 2 0 ms 0 ms 0 ms 192.168.0.2 3 1 ms 0 ms 0 ms 192.168.0.6 4 0 ms 0 ms 0 ms 192.168.0.26 5 0 ms 1 ms 0 ms 10.0.0.10 Trace complete. Even i ...

I don't think it is related to ospf.  do one more thing ... give the output  of  sh ip route ospf on R2  & R4 (Both cases  up/down)

I tried in gns3, but i have not faced any issue. Everything is working fine whether link is up or down: R5#Sh ip route ospf (link working R1 to R5)O 192.168.1.0/24 [110/2] via 15.1.1.1, 00:01:03, FastEthernet0/0O 192.168.2.0/24 [110/11] via 35.1.1.1,...

Dear AZIZ,  Perfect my friend, we are very close. Now the biggest question is that when link is removed between R1 & R5  then why there is no route of PC-1 and PC2 networks (It should not happen, coz R5 have ospf neighbor-ship with R2, R4 and R3 )?  ...