AR46 router version is VRP3.40-RT-00xx. Router Eth0/1 interface connects PC1 and router Eth0/2 connects PC2. Enable ACL on inbound direction of Eth0/2 interface and deny any source address to ping the interface. Enable ACL and PC2 cannot ping through Eth0/2 interface address. ACL is valid. PC1 can still ping Eth0/2 interface address and ACL is invalid.
Use ACL on outbound direction of Eth0/2 interface. PC1 and PC2 cannot ping through Eth0/2 interface address and ACL is valid.
PC2 pings Eth0/2 interface and the data enters into Eth0/2. For Eth0/2 interface, it is inbound direction and ACL is valid. PC1 pings Eth0/2 interface. For Eth0/2 interface, it is outbound direction and ACL is invalid.