- About This Guide
-
- Information about AAA
- Configuring the Local Database for AAA
- Configuring RADIUS Servers for AAA
- Configuring TACACS+ Servers for AAA
- Configuring LDAP Servers for AAA
- Configuring Windows NT Servers for AAA
- Configuring the Identity Firewall
- Configuring the ASA to Integrate with Cisco TrustSec
- Configuring Digital Certificates
- Index
Configuring NetFlow Secure Event Logging (NSEL)
This chapter describes how to configure NSEL, a security logging mechanism that is built on NetFlow Version 9 technology, and how to handle events and syslog messages through NSEL.
Information About NSEL
This section includes the following topics:
The ASA and ASASM support NetFlow Version 9 services. For more information about NetFlow services, see the “RFCs” section.
The ASA and ASASM implementations of NSEL provide a stateful, IP flow tracking method that exports only those records that indicate significant events in a flow. In stateful flow tracking, tracked flows go through a series of state changes. NSEL events are used to export data about flow status and are triggered by the event that caused the state change.
The significant events that are tracked include flow-create, flow-teardown, and flow-denied (excluding those flows that are denied by EtherType ACLs). In addition, the ASA and ASASM implementation of NSEL generates periodic NSEL events, flow-update events, to provide periodic byte counters over the duration of the flow. These events are usually time-driven, which makes them more in line with traditional NetFlow; however, they may also be triggered by state changes in the flow.
Note The flow-update event feature is not available in Version 9.0(1). It is available in Versions 8.4(5) and 9.1(2).
Each NSEL record has an event ID and an extended event ID field, which describes the flow event.
The ASA and ASASM implementations of NSEL provide the following major functions:
- Tracks flow-create, flow-teardown, and flow-denied events, and generates appropriate NSEL data records.
- Triggers flow-update events and generates appropriate NSEL data records.
- Defines and exports templates that describe the progression of a flow. Templates describe the format of the data records that are exported through NetFlow. Each event has several record formats or templates associated with it.
- Tracks configured NSEL collectors and delivers templates and data records to these configured NSEL collectors through NetFlow over UDP only.
- Sends template information periodically to NSEL collectors. Collectors receive template definitions, normally before receiving flow records.
- Filters NSEL events based on the traffic and event type through Modular Policy Framework, then sends records to different collectors. Traffic is matched based on the order in which classes are configured. After a match is found, no other classes are checked. The supported event types are flow-create, flow-denied, flow-teardown, flow-update, and all. Records can be sent to different collectors. For example, with two collectors, you can do the following:
– Log all flow-denied events that match ACL 1 to collector 1.
– Log all flow-create events to collector 1.
– Log all flow-teardown events to collector 2.
– Log all flow-update events to collector 1.
Using NSEL and Syslog Messages
Table 43-1 lists the syslog messages that have an equivalent NSEL event, event ID, and extended event ID. The extended event ID provides more detail about the event (for example, which ACL—ingress or egress—has denied a flow).
Note Enabling NetFlow to export flow information makes the syslog messages that are listed in Table 43-1 redundant. In the interest of performance, we recommend that you disable redundant syslog messages, because the same information is exported through NetFlow.
Note When NSEL and syslog messages are both enabled, there is no guarantee of chronological ordering between the two logging types.
Using NSEL in Clustering
Each ASA establishes its own connection to the collector(s). The fields in the header of the export packet include the system up time and UNIX time (synchronized across the cluster). These fields are all local to an individual ASA. The NSEL collector uses the combination of the source IP address and source port of the packet to separate different exporters.
Each ASA manages and advertises its template independently. Because the ASA supports in-cluster upgrades, different units may run different image versions at a certain point in time. As a result, the template that each ASA supports may be different.
Note Clustering is available on the ASA 5580 and 5585-X only. For more information about clustering, see Chapter10, “Configuring a Cluster of ASAs”
Licensing Requirements for NSEL
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Prerequisites for NSEL
Guidelines and Limitations
This section includes the guidelines and limitations for this feature.
Supported in single and multiple context mode.
Supported in routed and transparent firewall mode.
Supports IPv6 for the class-map , match access-list , and match any commands.
Additional Guidelines and Limitations
- If you have previously configured flow-export actions using the flow-export enable command, and you upgrade to a later version, then your configuration is automatically converted to the new Modular Policy Framework flow-export event-type command, which is described under the policy-map command.
- If you have previously configured flow-export actions using the flow-export event-type all command, and you upgrade to a later version, NSEL automatically begins issuing flow-update records when necessary.
- Flow-export actions are not supported in interface-based policies. You can configure flow-export actions in a class-map only with the match access-list , match any , or class-default commands. You can only apply flow-export actions in a global service policy.
- To view bandwidth usage for NetFlow records (not available in real-time), you must use the threat detection feature.
- Only the ASA 5580 and 5585-X support clustering.
Configuring NSEL
This section describes how to configure NSEL and includes the following topics:
Using NetFlow
The NetFlow pane lets you enable the transmission of data about a flow of packets. To access this pane, choose Configuration > Device Management > Logging > NetFlow .
Note IP address and hostname assignments should be unique throughout the NetFlow configuration.
To use NetFlow, perform the following steps:
Step 1 Enter the template timeout rate, which is the interval (in minutes) at which template records are sent to all configured collectors. The default value is 30 minutes.
Step 2 Enter the flow update interval, which specifies the time interval between flow-update events in minutes. Valid values are from 1 - 60 minutes. The default value is 1 minute.
Step 3 To delay the export of flow-creation events and process a single flow-teardown event instead of a flow-creation event and a flow-teardown event, check the Delay export of flow creation events for short-lived flows check box, then enter the number of seconds for the delay in the Delay By field.
Step 4 Specify the collector(s) to which NetFlow packets will be sent. You can configure a maximum of five collectors. To configure a collector, click Add to display the Add NetFlow Collector dialog box, and perform the following steps:
a. Choose the interface to which NetFlow packets will be sent from the drop-down list.
b. Enter the IP address or hostname and the UDP port number in the associated fields.
Step 5 To configure more collectors, repeat Step 4 for each additional collector.
Step 6 To change collector configuration details, select a collector and click Edit . To remove a configured collector, select it and click Delete .
Step 7 When NetFlow is enabled, certain syslog messages become redundant. To maintain system performance, we recommend that you disable all redundant syslog messages, because the same information is exported through NetFlow. To disable all redundant syslog messages, check the Disable redundant syslog messages check box. To display the redundant syslog messages and their status, click Show Redundant Syslog Messages .
The Redundant Syslog Messages dialog box appears. The Syslog ID field displays the redundant syslog message numbers. The Disabled field indicates whether or not the specified syslog message is disabled. Click OK to close this dialog box.
To disable individual redundant syslog messages, choose Configuration > Device Management > Logging > Syslog Setup .
Step 8 Click Apply to save your changes. Click Reset to enter new settings.
What to Do Next
See the “Matching NetFlow Events to Configured Collectors” section.
Matching NetFlow Events to Configured Collectors
After you configure NetFlow collectors, you can match a NetFlow event with any of these configured collectors.
To specify which NetFlow events should be sent to which collector, perform the following steps:
Step 1 In the ASDM main application window, choose Configuration > Firewall > Service Policy Rules .
Step 2 To add a service policy rule, perform the following steps:
a. Click Add to display the Add Service Policy Rule Wizard. For more information about service policy rules, see the firewall configuration guide.
b. Click the Global - applies to all interfaces radio button to apply the rule to the global policy. Click Next .
c. Check the Source and Destination IP Address (uses ACL) check box or the Any traffic check box as traffic match criteria, or click the Use class-default as traffic class radio button. Click Next to continue to the Rule Actions screen.
Note NetFlow actions are available only for global service policy rules and are applicable only to the class-default traffic class and to traffic classes with traffic match criteria of “Source and Destination IP Address (uses ACL)” or “Any traffic.”
Step 3 In the Rule Actions screen, click the NetFlow tab.
Step 4 To specify flow events, click Add to display the Add Flow Event dialog box, then perform the following steps:
a. Choose the flow event type from the drop-down list. Available events are created, torn down, denied, updated, or all.
Note The flow-update event is not available in Version 9.0(1). It is available in Versions 8.4(5) and 9.1(2).
b. Choose collectors to which you want events sent by checking the corresponding check boxes in the Send column.
c. To add, edit or delete collectors, or to configure other NetFlow settings (for example, syslog messages), click Manage to display the Manage NetFlow Collectors dialog box. Click OK to close the Manage NetFlow Collectors dialog box and return to the Add Flow Event dialog box. For more information about configuring collectors, see Step 4 of the “Using NetFlow” section.
Step 5 Click OK to close the Add Flow Event dialog box and return to the NetFlow tab.
Step 6 To change flow event entries, select an entry from the list, and click Edit . To remove flow event entries, select an entry from the list, and click Delete .
Step 7 Click Finish to exit the wizard.
Step 8 To edit a NetFlow service policy rule, perform the following steps:
a. Select it in the Service Policy Rules table, and click Edit .
b. Click the Rule Actions tab, then click the NetFlow tab.
What to Do Next
See the “Monitoring NSEL” section.
Monitoring NSEL
You can use syslog messages to help troubleshoot errors or monitor system usage and performance.You can view real-time syslog messages that have been saved in the log buffer in a separate window, which include an explanation of the message, details about the message, and recommended actions to take, if necessary, to resolve an error. For more information, see the “Using NSEL and Syslog Messages” section.
To monitor NSEL, see the following pane:
Where to Go Next
To configure the syslog server, see Chapter41, “Configuring Logging”
Additional References
For additional information related to implementing NSEL, see the following sections:
Related Documents
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Information about the implementation of NSEL on the ASA and ASA Services Module |
Cisco ASA 5500 Series Implementation Note for NetFlow Collectors See the following article at https://supportforums.cisco.com/docs/DOC-6113 . |
Configuring NetFlow on the ASA and ASA Services Module using ASDM |
See the following article at https://supportforums.cisco.com/docs/DOC-6114 . |
RFCs
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Feature History for NSEL
Table 43-2 lists each feature change and the platform release in which it was implemented. ASDM is backward-compatible with multiple platform releases, so the specific ASDM release in which support was added is not listed.