Understanding Acls - Cisco Catalyst 2960 Software Configuration Manual

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Configuring Network Security with ACLs

This chapter describes how to configure network security on the Catalyst 2960, 2960-S, or 2960-C

switch by using access control lists (ACLs), also referred to as access lists. Unless otherwise noted, the

term switch refers to a standalone switch and a switch stack.

Stacking is supported only on Catalyst 2960-S switches running the LAN base image.

If the switch is running the LAN Lite image, you can configure ACLs, but you cannot attach them to

physical interfaces. When it is running either the LAN Lite or LAN base image, you can attach ACLs to

VLAN interfaces to filter traffic to the CPU.

In this chapter, references to IP ACLs are specific to IP Version 4 (IPv4) 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 12.4, and the Cisco IOS IP Command

Reference, Volume 1 of 3: Addressing and Services, Release 12.4 on Cisco.com.

This chapter includes these sections:

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 switch and permit or deny packets crossing specified interfaces. 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

Understanding ACLs, page 31-1

Configuring IPv4 ACLs, page 31-6

Creating Named MAC Extended ACLs, page 31-23

Displaying IPv4 ACL Configuration, page 31-26

Catalyst 2960 and 2960-S Switches Software Configuration Guide, Release 15.0(1)SE

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