|  | 1.5 | Access List Overview
| 1.5.5 | Testing packets with access lists
For TCP/IP packet filters, Cisco IOS access lists check the packet and upper-layer headers. You will learn how to check packets for: Source IP addresses using standard access lists; identify these with a number in the range 1 to 99. Destination and source IP addresses or specific protocols using extended access lists; identify these with a number in the range 100 to 199. Upper-level TCP or UDP port numbers in addition to the other tests in extended access lists; also identify these with a number in the range 100 to 199. For all of these access lists, after a packet matches an access list statement, it can be denied or permitted using the selected interface.