ACL Syslog Correlation
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ACL Syslog CorrelationLast Updated: May 8, 2012
The 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 InformationYour 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 Table at the end of this document. Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required. Prerequisites for ACL Syslog CorrelationBefore 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 CorrelationACL Syslog Correlation TagsThe 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 MessagesWhen 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
Enabling Hash Value Generation on a RouterPerform 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. DETAILED STEPS ExamplesThe 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 101 Extended IP access list 101 10 permit tcp any any log (hash = 0x75F078B9) Router# show ip access-list acl Extended IP access list acl 10 permit tcp any any log (hash = 0x3027EB26) Disabling Hash Value Generation on a RouterPerform 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. DETAILED STEPS ExamplesThe 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 101 Extended IP access list 101 10 permit tcp any any log Router# show ip access-list acl Extended IP access list acl 10 permit tcp any any log Configuring ACL Syslog Correlation Using a User-Defined CookiePerform 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. The example in this section shows how to configure the ACL Syslog Correlation feature using a user-defined cookie for a numbered access list. However, you can configure the ACL Syslog Correlation feature using a user-defined cookie for both numbered and named access lists, and for both standard and extended access lists. DETAILED STEPS Configuring ACL Syslog Correlation Using a Hash ValuePerform 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. The steps in this section shows how to configure the ACL Syslog Correlation feature using a router-generated hash value for a numbered access list. However, you can configure the ACL Syslog Correlation feature using a router-generated hash value for both numbered and named access lists, and for both standard and extended access lists. DETAILED STEPS Changing the ACL Syslog Correlation Tag ValuePerform this task to change the value of the user-defined cookie or replace a router-generated hash value with a user-defined cookie. The steps in this section shows how to change the ACL Syslog Correlation tag value on a numbered access list. However, you can change the ACL Syslog Correlation tag value for both numbered and named access lists, and for both standard and extended access lists. DETAILED STEPS Troubleshooting TipsUse 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-generation Syslog hash code generation debugging is on Router# show debug IP ACL: Syslog hash code generation debugging is on Router# no debug ip access-list hash-generation Syslog hash code generation debugging is off Router# show debug Router# Configuration Examples for ACL Syslog Correlation
Example Configuring ACL Syslog Correlation Using a User-Defined CookieThe 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-generation Syslog MD5 hash code generation debugging is on Router# configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)# access-list 33 permit 10.10.10.6 log cook_33_std Router(config)# do show ip access 33 Standard IP access list 33 10 permit 10.10.10.6 log (tag = cook_33_std) Router(config)# end Router# Example Configuring ACL Syslog Correlation using a Hash ValueThe 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-generation Syslog MD5 hash code generation debugging is on Router# configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)# access-list 33 permit 10.10.10.7 log Router(config)# *Nov 7 13:51:23.615: %IPACL-HASHGEN: Hash Input: 33 standard permit 10.10.10.7 Hash Output: 0xCE87F535 Router(config)# do show ip access 33 Standard IP access list 33 10 permit 10.10.10.6 log (tag = cook_33_std) 20 permit 10.10.10.7 log (hash = 0xCE87F535) Router(config)# Example Changing the ACL Syslog Correlation Tag ValueThe 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 terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)# do show ip access-list 101 Extended IP access list 101 10 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 NewUDV Router(config)# do show access-list Extended IP access list 101 10 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 replacehash Router(config)# do show access-list Extended IP access list 101 10 permit tcp host 10.1.1.1 host 10.1.1.2 log (tag = NewUDV) 20 permit tcp any any log (tag = replacehash) Additional ReferencesRelated DocumentsMIBsTechnical Assistance
Feature Information for ACL Syslog CorrelationThe following table provides release information about the feature or features described in this module. This table 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. Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks. Third-party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1110R) Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental. © 2012 Cisco Systems, Inc. All rights reserved.
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