Table of Contents
What is an ACL?
- Use for Matching IP packets
- Filtering network traffic
- Enable router inbound and outbound interfaces
- It is a security feature, and acts as a security guard with the book of rules
- Think of it as someone(aka bodyguard) holding a list with the names of guests and standing in front of the door of a bar. When a guest turns up, he checks his/her name against the list. If there is a match permits otherwise he is denied access to the party.
- The default behavior of ACL is called implicit deny meaning if there is no match in the list, deny access.
Standard ACL
- Very limited
- 1 – 99
- Match using source IP only
- Match using specific IP ranges
- Operates only Layer 3 of the TCP/IP stack
- Does not understand L4 protocols
Extended ACL
- Match using both source & destination IPs
- Match using L4 protocols such as TCP, UDP, etc
- Match using port #s such as 443, 80, 53 etc.
- Operates on both L3/4 of the TCP/IP stack
