Access Control Lists (ACLs)

Access Control Lists (ACLs) are a set of rules defined on a router or switch interface to filter traffic. They can permit or deny packets based on source IP, destination IP, port numbers, and protocols.

Types of ACLs

1. Standard ACLs (1-99, 1300-1999)

• Filter based on Source IP Address only.
• Should be placed as close to the destination as possible.

2. Extended ACLs (100-199, 2000-2699)

• Filter based on Source IP, Destination IP, Protocol, and Port.
• Should be placed as close to the source as possible.

Wildcard Masks

ACLs use wildcard masks to define the scope of the address match. A 0 bit means "match exactly", and a 1 bit means "ignore".

• Host 192.168.1.1 -> 0.0.0.0
• Subnet 192.168.1.0/24 -> 0.0.0.255