Cisco Systems ME3400G2CSA Configuring Network Security with ACLs

CHAPTER

28-1

Cisco ME 3400 EthernetAccess Switch SoftwareConfiguration Guide

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Configuring Network Security with ACLs

This chapter describes how to configure network security on the Cisco ME 3400 Et hernet Access switch

by using access control lists (ACLs), which are also referred to in commands and tables as access lists.

Note Information in this chapter about IP ACLs is specific to IP Version 4 (IPv4).

For complete syntax and usage information for the commands used in this chapter, see the command

reference for this release, see the “Configuring IP Servi ces” 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.

This chapter consists of these sections:

•Understanding ACLs, page 28-1

•Configuring IPv4 ACLs, page 28-6

•Creating Named MAC Extended ACLs, page 28-26

•Configuring VLAN Maps, page 28-29

•Using VLAN Maps with Router ACLs, page 28-36

•Displaying IPv4 ACL Configuration, page 28-39

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 for warde d, base d o n th e

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.

You configure access lists on a router or Layer 3 switch to provide basic security for your network. If

you do not configure ACLs, all packets passing through the switch could be allowed onto all parts of the

network. You can use ACLs to control which hosts can access different parts of a network or to decide