ACL(Access Control List)

When configured, ACLs perform the following tasks:Limit network traffic to increase network performance。 For example, if corporate policy does not allow video traffic on the network, ACLs that block video traffic could be configured and applied。
This would greatly reduce the network load and increase network performance。 Provide traffic flow control。 ACLs can restrict the delivery of routing updates。
If updates are not required because of network conditions, bandwidth is preserved。 Provide a basic level of security for network access。
ACLs can allow one host to access a part of the network and prevent another host from accessing the same area。 For example, access to the Human Resources network can be restricted to authorized users。
Filter traffic based on traffic type。 For example, an ACL can permit email traffic, but block all Telnet traffic。 Screen hosts to permit or deny access to network services。
ACLs can permit or deny a user to access file types, such as FTP or HTTP。