Resolved! BGP route error in Routing table
From the R1 cannot ping to R3's loopback 192.168.5.1 although R1 have the route in routing table. And then R4 also cannot ping to R2's loopback 192.168.3.1 and R4 have no route in routing table for them. When I check R4 bgp table it show: r i 192.168...