Access List

Access lists are security and traffic control mechanisms that filter network traffic based on various criteria including source and destination IP addresses, ports, protocols, and other packet characteristics. They serve as fundamental building blocks for implementing security policies, Quality of Service (QoS), and network access control by permitting or denying traffic that matches specific conditions. Access lists can be applied to interfaces, routing protocols, and various network services to enforce granular traffic filtering and policy enforcement throughout the network infrastructure.

By defining granular rules for traffic filtering, Access Lists enhance network security, control resource access, and ensure efficient network operation. They are crucial for implementing security policies at the network edge and within internal segments.

• ACL Name (Standard/Extended)
• Entry Sequence Number
• Action (Permit/Deny)
• Source IP Address/Network
• Source Wildcard Mask
• Destination IP Address/Network (Extended ACLs)
• Destination Wildcard Mask (Extended ACLs)
• Protocol (Extended ACLs)
• Port Numbers (Extended ACLs)

You can use these Access List parameters to define precise traffic filtering rules for your network devices. Customize the type, entries, and matching criteria to fit your network’s security and operational needs. Adjusting these parameters lets you tailor access control for your environment.

The following configuration describes how to set up Standard and Extended IP Access Lists on an IOS-XE device. It lists how to define rules for permitting and denying traffic based on various criteria.

ip access-list standard StandardAccessList1
 10 permit 10.0.0.0 0.0.0.255
 20 permit 20.0.0.0 0.0.0.255
!
ip access-list extended ExtendedAccessList1
 10 permit ip any any
 20 deny ip any any

iosxe:
  devices:
    - name: Device1
      configuration:
        access_lists:
          standard:
            - name: StandardAccessList1
              entries:
                - sequence: 10
                  action: permit
                  prefix: 10.0.0.0
                  prefix_mask: 0.0.0.255
                - sequence: 20
                  action: permit
                  prefix: 20.0.0.0
                  prefix_mask: 0.0.0.255
          extended:
            - name: ExtendedAccessList1
              entries:
                - sequence: 10
                  action: permit
                  protocol: ip
                  source:
                    any: true
                  destination:
                    any: true
                - sequence: 20
                  action: deny
                  protocol: tcp
                  tcp_flags: [syn, ack]
                  source:
                    any: true
                  destination:
                    any: true