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Table Of Contents
Prerequisites for ACL Syslog Correlation
Information About ACL Syslog Correlation
How to Configure ACL Syslog Correlation
Enabling Hash Value Generation on a Router
Disabling Hash Value Generation on a Router
Configuring ACL Syslog Correlation Using a User-Defined Cookie
Configuring ACL Syslog Correlation Using a Hash Value
Changing the ACL Syslog Correlation Tag Value
Configuration Examples for ACL Syslog Correlation
Configuring ACL Syslog Correlation Using a User-Defined Cookie: Example
Configuring ACL Syslog Correlation using a Hash Value: Example
Changing the ACL Syslog Correlation Tag Value: Example
Feature Information for ACL Syslog Correlation
ACL Syslog Correlation
First Published: October 10, 2008Last Updated: October 10, 2008The Access Control List (ACL) Syslog Correlation feature appends a tag (either a user-defined cookie or a router-generated MD5 hash value) to access control entry (ACE) syslog entries. This tag uniquely identifies the ACE , within the ACL, that generated the syslog entry.
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 ACL Syslog Correlation" section.
Use Cisco Feature Navigator to find information about platform support and Cisco IOS, Catalyst OS, and Cisco IOS XE 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
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Prerequisites for ACL Syslog Correlation
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Prerequisites for ACL Syslog Correlation
Before you configure the ACL Syslog Correlation feature you should understand the concepts in the "IP Access List Overview" module.
The ACL Syslog Correlation feature appends a user-defined cookie or a router-generated hash value to ACE messages in the syslog. These values are only appended to ACE messages when the log option is enabled for the ACE.
Information About ACL Syslog Correlation
You should understand the following concepts before configuring the ACL Syslog Correlation feature:
ACL Syslog Correlation Tags
The ACL Syslog Correlation feature appends a tag (either a user-defined cookie or a router-generated MD5 hash value) to ACE syslog entries. This tag uniquely identifies the ACE that generated the syslog entry.
Network management software can use the tag to identify which ACE generated a specific syslog event. For example, network administrators can select an ACE rule in the network management application and can then view the corresponding syslog events for that ACE rule.
To append a tag to the syslog message, the ACE that generates the syslog event must have the log option enabled. The system appends only one type of tag (either a user-defined cookie or a router-generated MD5 hash value) to each message.
To specify a user-defined cookie tag, the user must enter the cookie value when configuring the ACE log option. The cookie must be in alpha-numeric form, it cannot be greater than 64 characters, and it cannot start with hex-decimal notation (such as 0x).
To specify a router-generated MD5 hash value tag, the hash-generation mechanism must be enabled on the router and the user must not enter a cookie value while configuring the ACE log option.
ACE Syslog Messages
When a packet is matched against an ACE in an ACL, the system checks whether the log option is enabled for that event. If the log option is enabled and the ACL Syslog Correlation feature is configured on the router, the system attaches the tag to the syslog message. The tag is displayed at the end of the syslog message, in addition to the standard information.
The following is a sample syslog message showing a user-defined cookie tag:
Jun 5 12:55:44.359: %SEC-6-IPACCESSLOGP: list logacl permitted tcp 192.168.16.1(38402) -> 192.168.16.2(23), 1 packet [User_permiited_ACE]The following is a sample syslog message showing a hash value tag:
Jun 5 12:55:44.359: %SEC-6-IPACCESSLOGP: list logacl permitted tcp 192.168.16.1(38402) -> 192.168.16.2(23), 1 packet [0x723E6E12]How to Configure ACL Syslog Correlation
This section includes the following tasks:
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Enabling Hash Value Generation on a Router
Perform this task to configure the router to generate an MD5 hash value for each log-enabled ACE in the system that is not configured with a user-defined cookie.
When the hash value generation setting is enabled, the system checks all existing ACEs and generates a hash value for each ACE that requires one. When the hash value generation setting is disabled, all previously generated hash values are removed from the system.
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DETAILED STEPS
Examples
The following is sample output from the show ip access-list command when hash generation is enabled for the specified access-list.
Router# show ip access-list 101Extended IP access list 10110 permit tcp any any log (hash = 0x75F078B9)Router# show ip access-list aclExtended IP access list acl10 permit tcp any any log (hash = 0x3027EB26)Disabling Hash Value Generation on a Router
Perform this task to disable hash value generation on the router. When the hash value generation setting is disabled, all previously generated hash values are removed from the system.
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Examples
The following is sample output from the show ip access-list command when hash generation is disabled and no cookie value has been specified.
Router# show ip access-list 101Extended IP access list 10110 permit tcp any any logRouter# show ip access-list aclExtended IP access list acl10 permit tcp any any logConfiguring ACL Syslog Correlation Using a User-Defined Cookie
Perform this task to configure the ACL Syslog Correlation feature on a router for a specific access list, using a user-defined cookie as the syslog message tag.
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Restrictions
The following restrictions apply when choosing the user-defined cookie value:
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SUMMARY STEPS
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Examples
The following is sample output from the show ip access-list command for an access list with a user-defined cookie value.
Router# show ip access-list 101Extended IP access list 10130 permit tcp host 10.1.1.1 host 10.1.1.2 log (tag = UserDefinedValue)Configuring ACL Syslog Correlation Using a Hash Value
Perform this task to configure the ACL Syslog Correlation feature on a router for a specific access list, using a router-generated hash value as the syslog message tag.
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DETAILED STEPS
Examples
The following is sample output from the show ip access-list command for an access list with a router-generated hash value.
Router# show ip access-list 102Extended IP access list 10210 permit tcp host 10.1.1.1 host 10.1.1.2 log (hash = 0x7F9CF6B9)Changing the ACL Syslog Correlation Tag Value
Perform this task to change the value of the user-defined cookie or replace a router-generated hash value with a user-defined cookie.
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Troubleshooting Tips
Use the debug ip access-list hash-generation command to display access list debug information. The following is an example of the debug command output:
Router# debug ip access-list hash-generationSyslog hash code generation debugging is onRouter# show debugIP ACL:Syslog hash code generation debugging is onRouter# no debug ip access-list hash-generationSyslog hash code generation debugging is offRouter# show debugRouter#Configuration Examples for ACL Syslog Correlation
This section provides the following configuration examples:
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Configuring ACL Syslog Correlation Using a User-Defined Cookie: Example
The following example shows how to configure the ACL Syslog Correlation feature on a router using a user-defined cookie.
Router#Router# debug ip access-list hash-generationSyslog MD5 hash code generation debugging is onRouter# configure terminalEnter configuration commands, one per line. End with CNTL/Z.Router(config)# access-list 33 permit 10.10.10.6 log cook_33_stdRouter(config)# do show ip access 33Standard IP access list 3310 permit 10.10.10.6 log (tag = cook_33_std)Router(config)# endRouter#Configuring ACL Syslog Correlation using a Hash Value: Example
The following examples shows how to configure the ACL Syslog Correlation feature on a router using a router-generated hash value.
Router# debug ip access-list hash-generationSyslog MD5 hash code generation debugging is onRouter# configure terminalEnter configuration commands, one per line. End with CNTL/Z.Router(config)# access-list 33 permit 10.10.10.7 logRouter(config)#*Nov 7 13:51:23.615: %IPACL-HASHGEN: Hash Input: 33 standard permit 10.10.10.7Hash Output: 0xCE87F535Router(config)# do show ip access 33Standard IP access list 3310 permit 10.10.10.6 log (tag = cook_33_std)20 permit 10.10.10.7 log (hash = 0xCE87F535)Router(config)#Changing the ACL Syslog Correlation Tag Value: Example
The following example shows how to replace an existing access list user-defined cookie with a new cookie value, and how to replace a router-generated hash value with a user-defined cookie value.
Router# configure terminalEnter configuration commands, one per line. End with CNTL/Z.Router(config)# do show ip access-list 101Extended IP access list 10110 permit tcp host 10.1.1.1 host 10.1.1.2 log (tag = MyCookie)20 permit tcp any any log (hash = 0x75F078B9)Router(config)# access-list 101 permit tcp host 10.1.1.1 host 10.1.1.2 log NewUDVRouter(config)# do show access-listExtended IP access list 10110 permit tcp host 10.1.1.1 host 10.1.1.2 log (tag = NewUDV)20 permit tcp any any log (hash = 0x75F078B9)Router(config)# access-list 101 permit tcp any any log replacehashRouter(config)# do show access-listExtended IP access list 10110 permit tcp host 10.1.1.1 host 10.1.1.2 log (tag = NewUDV)20 permit tcp any any log (tag = replacehash)Additional References
The following sections provide references related to the ACL Syslog Correlation feature.
Related Documents
Standards
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature
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MIBs
None
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:
RFCs
Technical Assistance
Feature Information for ACL Syslog Correlation
Table 1 lists the release history for this feature. For information on a feature in this technology that is not documented here, see the IP Access List Roadmap.
Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS, Catalyst OS, and Cisco IOS XE 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
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