Chapter 26 Configuring Network Security With Acls; Understanding Acls - Cisco 3020 - Catalyst Blade Switch Configuration Manual

Configuring Network Security with ACLs
This chapter describes how to configure network security on the switch by using access control lists
(ACLs), which in commands and tables are also referred to as access lists.
Information in this chapter about IP ACLs is specific to IP Version 4 (IPv4).
Note
For complete syntax and usage information for the commands used in this chapter, see the command
reference for this release, see 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.
This chapter consists of these sections:
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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 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.
OL-8915-01
Understanding ACLs, page 26-1
Configuring IPv4 ACLs, page 26-5
Creating Named MAC Extended ACLs, page 26-21
Configuring VLAN Maps, page 26-23
Displaying IPv4 ACL Configuration, page 26-30
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