cannot suddenly ping to a certain host even though it worked before and it works vise versa

I cannot ping only to a one certain host $B from an only certain host $A, even though it worked before. * [A] ping $B --> destination host unreachable * [B] ping $A works. * [C] ping $B works. * [A] traceroute $B result:

1. $B 3005.339 ms !H 3005.277 ms !H 3005.250 ms !H

Host $B has 2 ethernet interfaces (eth0 - by default, eth1 - for drbd, DEFROUTE=no for eth1), and used as primary node. eth0 and eth1 are located in different subnets. Both hosts A and B, C are located in a same subnet and have CentOS 7 installed.