Understanding Acls - Cisco ME 3400 Software Configuration Manual

Configuring Network Security with ACLs
This chapter describes how to configure network security on the Cisco ME 3400 Ethernet Access switch
by using access control lists (ACLs), which are also referred to in commands and tables as access lists.
Information in this chapter about IP ACLs is specific to IP Version 4 (IPv4). For information about
Note
configuring IPv6 ACLs, see
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 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.
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
OL-9639-07
Chapter 37, "Configuring IPv6 ACLs."
Understanding ACLs, page 31-1
Configuring IPv4 ACLs, page 31-6
Creating Named MAC Extended ACLs, page 31-26
Configuring VLAN Maps, page 31-29
Using VLAN Maps with Router ACLs, page 31-35
Displaying IPv4 ACL Configuration, page 31-39
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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
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