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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter12 Configuring Network Security with ACLs
Configuring ACLs
This example shows how to apply access list 2 on Gigabit Ethernet interface 0/3 to filter packets entering
the interface:
Switch(config)# interface gigabitethernet0/3
Router(config-if)# ip access-group 2 in
Note The ip access-group interface configuration command is only valid when applied to an management
interface, a Layer 2 interface, or a Layer 3 interface. If applied to a Layer 3 interface, the interface must
have been configured with an IP address. 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 ACLs
You can display existing ACLs by using show commands.
Beginning in privileged EXEC mode, follow these steps to display access lists:
This example displays all standard and extended ACLs:
Switch# show access-lists
Standard IP access list 1
permit 172.20.10.10
Standard IP ACL 10
permit 12.12.12.12
Standard IP access list 12
deny 1.3.3.2
Standard IP access list 32
permit 172.20.20.20
Standard IP access list 34
permit 10.24.35.56
permit 23.45.56.34
Extended IP access list 120
Extended MAC access list mac1
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.
Command Purpose
Command Purpose
Step 1
show access-lists [number | name] Show information about all IP and MAC address access lists or about a
specific access list (numbered or named).
Step 2
show ip access-list [number | name] Show information about all IP address access lists or about a specific IP
ACL (numbered or named).
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