28-20
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
78-11380-12
Chapter 28 Configuring Network Security with ACLs
Displaying ACL Information
Applying ACLs to a Physical Interface
Beginning in privileged EXEC mode, follow these steps to control access to a Layer 2 interface:
This example shows how to apply access list 2 on an interface to filter packets entering the interface:
Switch(config)# interface gigabitethernet0/2
Router(config-if)# ip access-group 2 in
Note The ip access-group interface configuration command is only valid when applied to a management
interface or a Layer 2 physical interface. ACLs cannot be applied to interface port-channels.
For inbound ACLs, after receiving a packet, the switch checks the packet against the ACL. If the ACL
permits the packet, the switch continues to process the packet. If the ACL rejects the packet, the switch
discards the packet.
When you apply an undefined ACL to an interface, the switch acts as if the ACL has not been applied to
the interface and permits all packets. Remember this behavior if you use undefined ACLs for network
security.
Displaying ACL Information
You can display the ACLs that are configured on the switch, and you can display the ACLs that have
been applied to physical and management interfaces. This section consists of these topics:
• Displaying ACLs, page 28-20
• Displaying Access Groups, page 28-22
Displaying ACLs
You can display existing ACLs by using show commands.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Identify a specific interface for configuration and enter interface
configuration mode.
The interface must be a Layer 2 or management interface or a management
interface VLAN ID.
Step 3
ip access-group {access-list-number |
name} {in}
Control access to the specified interface.
Step 4
end Return to privileged EXEC mode.
Step 5
show running-config Display the access list configuration.
Step 6
copy running-config startup-config (Optional) Save your entries in the configuration file.
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