Is the host at 172.20.11.250 on the same subnet as the host at 172.20.12.3? how do you know? Following the explanation mentioned above 172.20.11.250 host belongs to subnet 172.20.11.0 and host 172.20.6.255 host belong to subnet 172.20.6.0 hence both these hosts belong to different subnets. Since the value for host 172.20.11.250(11) specifies that it belongs to subnet 172.20.11.0 and 172.20.6.255(6) specifies that it belongs to subnet 172.20.6.0.