router configured with a standard IPv4 ACL extracts the source IPv4 address from packet header. router starts at the top of the ACL and compares the address to each ACE sequentially. when match, the router carries out the instruction, After a match is made, the remaining ACEs in the ACL, if any, are not analyzed. If the source IPv4 address does not match any ACEs in the ACL, the packet is discarded.