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Catalyst 3560 Switch Software Configuration Guide
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Configuring Network Security with ACLs
This chapter describes how to configure network security on the Catalyst 3560 switch by using access
control lists (ACLs), which in commands and tables are also referred to as access lists.
Note Information in this chapter about IP ACLs is specific to IP Version 4 (IPv4). For information about IPv6
ACLs, see Chapter 39, “Configuring IPv6 ACLs.”
For complete syntax and usage information for the commands used in this chapter, see the command
reference for this release, the “Configuring IP Services” section in the “IP Addressing and Services”
chapter of the Cisco IOS IP Configuration Guide, Release 12.2, and the Cisco IOS IP Command
Reference, Volume 1 of 3: Addressing and Services, Release 12.2. The Cisco IOS documentation is
available from the Cisco.com page under Documentation > Cisco IOS Software > 12.2 Mainline >
Configuration Guides or Command References.
This chapter consists of these sections:
Understanding ACLs, page 33-1
Configuring IPv4 ACLs, page 33-6
Creating Named MAC Extended ACLs, page 33-27
Configuring VLAN Maps, page 33-29
Using VLAN Maps with Router ACLs, page 33-36
Displaying IPv4 ACL Configuration, page 33-40

Understanding ACLs

Packet filtering can help limit network traffic and restrict network use by certain users or devices. ACLs
filter traffic as it passes through a router or switch and permit or deny packets crossing specified
interfaces or VLANs. An ACL is a sequential collection of permit and deny conditions that apply to
packets. When a packet is received on an interface, the switch compares the fields in the packet against
any applied ACLs to verify that the packet has the required permissions to be forwarded, based on the
criteria specified in the access lists. One by one, it tests packets against the conditions in an access list.
The first match decides whether the switch accepts or rejects the packets. Because the switch stops
testing after the first match, the order of conditions in the list is critical. If no conditions match, the
switch rejects the packet. If there are no restrictions, the switch forwards the packet; otherwise, the
switch drops the packet. The switch can use ACLs on all packets it forwards, including packets bridged
within a VLAN.