Cisco IOS Security Configuration Guide: Securing the Data Plane, Release 12.4

Displaying and Clearing IP Access List Data Using ACL Manageability

This module describes how to display the entries in an IP access list and the number of packets that have matched each entry. Users can get these statistics globally, or per interface and per incoming or outgoing traffic direction, by using the ACL Manageability feature. Viewing details of incoming and outgoing traffic patterns on various interfaces of a network device can help secure devices against attacks coming in on a particular interface. This module also describes how to clear counters so that the count of packets matching an access list entry will restart from zero.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for Displaying IP Access List Information and Clearing Counters" section.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

•Information About Displaying and Clearing IP Access List Data Using ACL Manageability

•How to Display and Clear IP Access List Data

•Configuration Examples for Displaying and Clearing IP Access List Data Using ACL Manageability

•Additional References

•Feature Information for Displaying IP Access List Information and Clearing Counters

Information About Displaying and Clearing IP Access List Data Using ACL Manageability

•Benefits of ACL Manageability

•Support for Interface-Level ACL Statistics

Benefits of ACL Manageability

Prior to Cisco IOS Release 12.4(6)T, the ACL infrastructure in Cisco IOS software maintained only global statistics for each ACE in an ACL. With this method, if an ACL is applied to multiple interfaces, the maintained ACE statistics are the sum of incoming and outgoing packet matches (hits) on all the interfaces on which that ACL is applied.

However, if ACE statistics are maintained per interface and per incoming or outgoing traffic direction, users can view specific details of incoming and outgoing traffic patterns and the effectiveness of ACEs on the various interfaces of a network device. This type of information is useful for securing devices against attacks coming in on a particular interface.

Support for Interface-Level ACL Statistics

With Cisco IOS Release 12.4(6)T, the ACL infrastructure in Cisco IOS software is now extended to support the maintenance, display, and clearing of ACE statistics per interface and per incoming or outgoing traffic direction for ACLs. This support is often referred to as "support for interface-level statistics."

Note If the same access-group ACL is also used by other features, the maintained interface statistics are not updated when a packet match is detected by the other features. In this case, the sum of all the interface level statistics that are maintained for an ACL may not add up to the global statistics for that ACL.

How to Display and Clear IP Access List Data

This section contains the following procedures for displaying IP access lists and the counts of packets that match (hit) each list, and for clearing IP access list counters.

Note Alternatively, if you want to deny access to a particular host or network and find out if someone from that network or host is attempting to gain access, include the log keyword with the corresponding deny statement so that the packets denied from that source are logged for you. For more information, see the "IP Access List Logging" section of the "IP Access List Overview."

•Displaying Global IP ACL Statistics

•Displaying Interface-Level IP ACL Statistics

•Clearing the Access List Counters

Displaying Global IP ACL Statistics

Perform this task to display all IP access lists on the router and counts of packets that have matched.

SUMMARY STEPS

1. enable

2. show ip access-list [access-list-number | access-list-name]

DETAILED STEPS

Displaying Interface-Level IP ACL Statistics

This section describes how to display IP ACE statistics per interface and per incoming or outgoing traffic direction for ACLs. This feature is known as ACL Manageability.

Restrictions for ACL Manageability

•ACL Manageability supports:

–Only nondistributed software switched platforms.

–Standard and extended statically configured ACLs, and Threat Mitigation Service (TMS) dynamic ACEs.

•ACL Manageability does not support:

–Reflexive and user-configured dynamic ACLs and dynamic ACE blocks, such as Firewall and Authentication Proxy.

–Virtual-template and virtual-access interfaces.

SUMMARY STEPS

1. enable

2. show ip access-list interface interface-name [in | out]

DETAILED STEPS

Clearing the Access List Counters

The system counts how many packets match (hit) each line of an access list; the counters are displayed by the show access-lists EXEC command. Perform this task to clear the counters of an access list. You might do this if you are trying to determine a more recent count of packets that match an access list, starting from zero.

SUMMARY STEPS

1. enable

2. clear ip access-list counters {access-list-number | access-list-name}

DETAILED STEPS

Configuration Examples for Displaying and Clearing IP Access List Data Using ACL Manageability

•Example: Displaying Global IP ACL Statistics

•Example: Displaying Input Statistics

•Example: Displaying Output Statistics

•Example: Displaying Input and Output Statistics

•Example: Clearing Global and Interface Statistics for an IP Access List

•Example: Clearing Global and Interface Statistics for All IP Access Lists

Example: Displaying Global IP ACL Statistics

The following example displays global statistics for ACL 150:

Router# show ip access-list 150 

Extended IP access list 150 

   10 permit ip host 10.1.1.1 any (3 matches)

   30 permit ip host 10.2.2.2 any (27 matches)

Example: Displaying Input Statistics

The following example displays statistics on incoming packets gathered from the FastEthernet interface 0/1, associated with access list 150 (ACL number):

Router# show ip access-list interface FastEthernet 0/1 in

Extended IP access list 150 in

   10 permit ip host 10.1.1.1 any (3 matches)

   30 permit ip host 10.2.2.2 any (12 matches)

Example: Displaying Output Statistics

The following example displays statistics on outgoing packets gathered from the FastEthernet interface 0/0:

Router# show ip access-list interface FastEthernet 0/0 out

Extended IP access list myacl out

    5 deny ip any 10.1.0.0 0.0.255.255

    10 permit udp any any eq snmp (6 matches)

Example: Displaying Input and Output Statistics

Note If no direction is specified, any input and output ACLs applied to that interface are displayed.

The following example displays input and output statistics gathered from the FastEthernet interface 0/0:

Router# show ip access-list interface FastEthernet 0/0

Extended IP access list 150 in

   10 permit ip host 10.1.1.1 any 

   30 permit ip host 10.2.2.2 any (15 matches)

Extended IP access list myacl out

    5 deny ip any 10.1.0.0 0.0.255.255

    10 permit udp any any eq snmp (6 matches)

Example: Clearing Global and Interface Statistics for an IP Access List

The following example clears global and interface statistics for IP ACL 150:

Router# clear ip access-list counters 150

Example: Clearing Global and Interface Statistics for All IP Access Lists

The following example clears global and interface statistics for all IP ACLs:

Router# clear ip access-list counters

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for Displaying IP Access List Information and Clearing Counters

Table 1 lists the features in this module and provides links to specific configuration information.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 1 lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

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