Access Control List on Cisco Switch

 Access Control List on Cisco Switch

Cisco switches support both standard and extended Access Control Lists (ACLs). Here are some details about each:

Standard ACLs:

• Number Range: Standard ACLs are numbered from 1 to 99.
• Matching Criteria: Standard ACLs can filter traffic based only on the source IP address.
• Syntax: The syntax for configuring a standard ACL is:

  arduino
  access-list <1-99> {permit|deny} <source> [source-wildcard]
  

Extended ACLs:

• Number Range: Extended ACLs are numbered from 100 to 199.
• Matching Criteria: Extended ACLs can filter traffic based on various criteria such as source/destination IP address, source/destination port numbers, and protocol type.
• Syntax: The syntax for configuring an extended ACL is more complex. It allows for specifying source and destination IP addresses, source and destination port numbers, and protocol type. Here's a basic syntax example:

  php
  access-list <100-199> {permit|deny} <protocol> <source> <source-wildcard> <destination> <destination-wildcard> [<operator> <port>]
  

Common Operators for Extended ACLs:

• eq: Equal to a specific port number.
• gt: Greater than a specific port number.
• lt: Less than a specific port number.
• range: Range of port numbers.
• any: Any port number.
• established: Matches TCP packets that have the ACK or RST bits set, indicating an established connection.

Applying ACLs:

ACLs can be applied to VLAN interfaces, physical interfaces, or SVIs (Switched Virtual Interfaces) using the ip access-group command in interface configuration mode.

Guidelines:

• Placement: ACLs should be placed as close to the source of traffic as possible to minimize unnecessary processing.
• Order: ACLs are processed in the order they are configured, so the more specific entries should precede more general ones.
• Logging: It's recommended to enable logging for denied traffic to aid in troubleshooting.

Understanding and effectively using ACLs is crucial for network security and traffic management on Cisco switches.