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ACL Configuring
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Chapter 18. ACL Configuring
18.1 Brief Introduction to ACL
As network scale and network traffic are increasingly growing, network security and
bandwidth allocation become more and more critical to network management. Packet filtering
can be used to efficiently prevent illegal users from accessing networks and to control
network traffic and save network resources. Access control lists (ACL) are often used to filter
packets with configured matching rules.
ACLs are sets of rules (or sets of permit or deny statements) that decide what packets can
pass and what should be rejected based on matching criteria such as source MAC address,
destination MAC address, source IP address, destination IP address, and port number.
When an ACL is assigned to a piece of hardware and referenced by a QoS
policy for traffic classification, the switch does not take action according to
the traffic behavior definition on a packet that does not match the ACL.
ACL according to application identified by ACL numbers, fall into three categories,
Basic ACL: Source IP address
Extended ACL: Source IP address, destination IP address, protocol carried on IP, and
other Layer 3 or Layer 4 protocol header information
Layer 2 ACL: Layer 2 protocol header fields such as source MAC address, destination
MAC address, 802.1p priority, and link layer protocol type
18.1.1 Configuring Match Order
An ACL consists of multiple rules, each of which specifies different matching criteria.
These criteria may have overlapping or conflicting parts. This is where the order in which a
packet is matched against the rules comes to rescue.
Two match orders are available for ACLs:
config: where packets are compared against ACL rules in the order in which they are
configured.
auto: where depth-first match is performed. The term depth-first match has different
meanings for different types of ACLs. Depth-first match for a basic ACL
For example, now configuring 2 types of ACL as below
:
Switch(config)#access-list 2000 deny any
Config ACL subitem successfully.
Switch(config)#access-list 2000 permit 1.1.1.1 0