Table Of Contents

Configuring NetFlow Secure Event Logging (NSEL)

Information About NSEL

Using NSEL and Syslog Messages

Licensing Requirements for NSEL

Prerequisites for NSEL

Guidelines and Limitations

Configuring NSEL

Configuring NSEL Collectors

Configuring Flow-Export Actions Through Modular Policy Framework

Configuring Template Timeout Intervals

Delaying Flow-Create Events

Disabling and Reenabling NetFlow-related Syslog Messages

Clearing Runtime Counters

Monitoring NSEL

Configuration Examples for NSEL

Additional References

Related Documents

RFCs

Feature History for NSEL

Configuring NetFlow Secure Event Logging (NSEL)

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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.

The chapter includes the following sections:

•Information About NSEL

•Licensing Requirements for NSEL

•Prerequisites for NSEL

•Guidelines and Limitations

•Configuring NSEL

•Monitoring NSEL

•Configuration Examples for NSEL

•Additional References

•Feature History for NSEL

Information About NSEL

The ASA supports NetFlow Version 9 services. For more information about NetFlow services, see RFCs.

The ASA implementation of NSEL is 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). Each NSEL record has an event ID and an extended event ID field, which describes the flow event.

The ASA implementation of NSEL provides the following major functions:

•Keeps track of flow-create, flow-teardown, and flow-denied 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, and 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, 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 access-list 1 to collector 1.

–Log all flow-create events to collector 1.

–Log all flow-teardown events to collector 2.

•Delays the export of flow-create events.

Using NSEL and Syslog Messages

Table 75-1 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).

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Note Enabling NetFlow to export flow information makes the syslog messages that are listed in Table 75-1 redundant. In the interest of performance, we recommend that you disable redundant syslog messages, because the same information is exported through NetFlow. You can enable or disable individual syslog messages by following the procedure in the "Disabling and Reenabling NetFlow-related Syslog Messages" section.

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Table 75-1 Syslog Messages and Equivalent NSEL Events 

Syslog Message	Description	NSEL Event ID	NSEL Extended Event ID
106100	Generated whenever an ACL is encountered.	1—Flow was created (if the ACL allowed the flow). 3—Flow was denied (if the ACL denied the flow).	0—If the ACL allowed the flow. 1001—Flow was denied by the ingress ACL. 1002—Flow was denied by the egress ACL.
106015	A TCP flow was denied because the first packet was not a SYN packet.	3—Flow was denied.	1004—Flow was denied because the first packet was not a TCP SYN packet.
106023	When a flow was denied by an ACL attached to an interface through the access-group command.	3—Flow was denied.	1001—Flow was denied by the ingress ACL. 1002—Flow was denied by the egress ACL.
302013, 302015, 302017, 302020	TCP, UDP, GRE, and ICMP connection creation.	1—Flow was created.	0—Ignore.
302014, 302016, 302018, 302021	TCP, UDP, GRE, and ICMP connection teardown.	2—Flow was deleted.	0—Ignore. > 2000—Flow was torn down.
313001	An ICMP packet to the device was denied.	3—Flow was denied.	1003—To-the-box flow was denied because of configuration.
313008	An ICMP v6 packet to the device was denied.	3—Flow was denied.	1003—To-the-box flow was denied because of configuration.
710003	An attempt to connect to the device interface was denied.	3—Flow was denied.	1003—To-the-box flow was denied because of configuration.

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Note When NSEL and syslog messages are both enabled, there is no guarantee of chronological ordering between the two logging types.

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Licensing Requirements for NSEL

The following table shows the licensing requirements for this feature:

Model	License Requirement
All models	Base License.

Prerequisites for NSEL

NSEL has the following prerequisites:

•IP address and hostname assignments must be unique throughout the NetFlow configuration.

•You must have at least one configured collector before you can use NSEL.

•You must configure NSEL collectors before you can configure filters via Modular Policy Framework.

Guidelines and Limitations

This section includes the guidelines and limitations for this feature:

Context Mode Guidelines

Supported in single and multiple context modes.

Firewall Mode Guidelines

Supported in routed and transparent firewall modes.

IPv6 Guidelines

Supports IPv6 for the class-map, match access-list, and match any commands.

Additional Guidelines and Limitations

•If you previously configured flow-export actions using the flow-export enable command, and you upgrade to a later version, then your configuration will be automatically converted to the new Modular Policy Framework flow-export event-type command, described under the policy-map command. For more information, see the Release Notes for the Cisco ASA 5500 Series for Version 8.1(2).

•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.

Configuring NSEL

This section describes how to configure NSEL, and includes the following topics:

•Configuring NSEL Collectors

•Configuring Flow-Export Actions Through Modular Policy Framework

•Configuring Template Timeout Intervals

•Delaying Flow-Create Events

•Disabling and Reenabling NetFlow-related Syslog Messages

•Clearing Runtime Counters

Configuring NSEL Collectors

To configure NSEL collectors, enter the following command:

Command

Purpose

flow-export destination interface-name ipv4-address|hostname udp-port Example: hostname (config)# flow-export destination inside 209.165.200.225 2002

Configures an NSEL collector to which NetFlow packets are sent. The destination keyword indicates that a NSEL collector is being configured. The interface-name argument is the name of the ASA interface through which the collector is reached. The ipv4-address argument is the IP address of the machine running the collector application. The hostname argument is the destination IP address or name of the collector. The udp-port argument is the UDP port number to which NetFlow packets are sent. You can configure a maximum of five destinations. After a destination is configured, template records are automatically sent to all configured NSEL collectors. Note Make sure that collector applications use the Event Time field to correlate events.

Configuring Flow-Export Actions Through Modular Policy Framework

To export NSEL events by defining all classes with flow-export actions, perform the following steps:

	Command	Purpose
Step 1	class-map flow_export_class Example: hostname (config-pmap)# class-map flow_export_class	Defines the class map that identifies traffic for which NSEL events need to be exported. The flow_export_class argument is the name of the class map.
Step 2	Do one of the following:
	match access-list flow_export_acl Example: hostname (config-cmap)# match access-list flow_export_acl	Configures the access list to match specific traffic. The flow_export_acl argument is the name of the access list.
	match any Example: hostname (config-cmap)# match any	Matches any traffic.
Step 3	policy-map flow_export_policy Example: hostname(config)# policy-map flow_export_policy	Defines the policy map to apply flow-export actions to the defined classes. The flow_export_policy argument is the name of the policy map. Note If you create a new policy map and apply it globally according to Step 6, the rest of the inspection policies will be deactivated. Alternatively, to insert a NetFlow class in the existing policy, enter the class flow_export_class command after the policy-map global_policy command. For more information about creating or modifying Modular Policy Framework, see the "Configuring Modular Policy Framework" section.
Step 4	class flow_export_class Example: hostname (config-pmap)# class flow_export_class	Defines the class to apply flow-export actions. The flow_export_class argument is the name of the class.
Step 5	flow-export event-type event-type destination flow_export_host1 [flow_export_host2] Example: hostname (config-pmap-c)# flow-export event-type all destination 209.165.200.230	Configures a flow-export action. The event_type keyword is the name of the supported event being filtered. The supported event types are flow-create, flow-denied, flow-teardown, and all. The flow_export_host argument is the IP address of a host. The destination keyword is the IP address of the configured collector.
Step 6	service-policy flow_export_policy global Example: hostname (config)# service-policy flow_export_policy global	Attaches the service policy globally. The flow_export_policy argument is the name of the policy map.

Configuring Template Timeout Intervals

To configure template timeout intervals, enter the following command:

Command	Purpose
flow-export template timeout-rate minutes Example: hostname (config)# flow-export template timeout-rate 15	Specifies the interval at which template records are sent to all configured output destinations. The template keyword indicates the template-specific configurations. The timeout-rate keyword specifies the time before templates are resent. The minutes argument specifies the time interval in minutes at which the templates are resent. The default value is 30 minutes.

Delaying Flow-Create Events

To delay the sending of flow-create events, enter the following command:

Command	Purpose
flow-export delay flow-create seconds Example: hostname (config)# flow-export delay flow-create 10	Delays the sending of a flow-create event. The seconds argument indicates the amount of time allowed for the delay in seconds. If this command is not configured, there is no delay, and the flow-create event is exported as soon as the flow is created. If the flow is torn down before the configured delay, the flow-create event is not sent; an extended flow teardown event is sent instead.

Disabling and Reenabling NetFlow-related Syslog Messages

To disable and reenable NetFlow-related syslog messages, perform the following steps:

	Command	Purpose
Step 1	logging flow-export syslogs disable Example: hostname(config)# logging flow-export syslogs disable	Disables syslog messages that have become redundant because of NSEL. Note Although you execute this command in global configuration mode, it is not stored in the configuration. Only the no logging message xxxxxx commands are stored in the configuration.
Step 2	logging message xxxxxx Example: hostname(config)# logging message 302013	Reenables syslog messages individually, where xxxxxx is the specified syslog message that you want to reenable.
Step 3	logging flow-export syslogs enable Example: hostname(config)# logging flow-export syslogs enable	Reenables all NSEL events at the same time.

Clearing Runtime Counters

To reset runtime counters, enter the following command:

Command	Purpose
clear flow-export counters Examples hostname# clear flow-export counters	Resets all runtime counters for NSEL to zero.

Monitoring NSEL

To monitor NSEL, enter one of the following commands:

Command	Purpose
show flow-export counters	Shows runtime counters, including statistical data and error data, for NSEL.
show logging flow-export-syslogs	Lists all syslog messages that are captured by NSEL events.
show running-config logging	Shows disabled syslog messages, which are redundant syslog messages, because they export the same information through NetFlow.

Examples

hostname (config)# show flow-export counters

destination: inside 209.165.200.225 2055

Statistics:

packets sent                 250

Errors:

block allocation errors        0

invalid interface              0

template send failure          0

hostname# show logging flow-export-syslogs

Syslog ID       Type                           Status 

302013          Flow Created                   Enabled 

302015          Flow Created                   Enabled 

302017          Flow Created                   Enabled 

302020          Flow Created                   Enabled 

302014          Flow Deleted                   Enabled 

302016          Flow Deleted                   Enabled 

302018          Flow Deleted                   Enabled 

302021          Flow Deleted                   Enabled 

106015          Flow Denied                    Enabled 

106023          Flow Denied                    Enabled 

313001          Flow Denied                    Enabled 

313008          Flow Denied                    Enabled 

710003          Flow Denied                    Enabled 

106100          Flow Created/Denied            Enabled 

hostname (config)# show running-config logging

no logging message 313008

no logging message 313001

Configuration Examples for NSEL

The following examples show how to filter NSEL events, with these collectors already configured:

•flow-export destination inside 209.165.200.230

•flow-export destination outside 209.165.201.29 2055

•flow-export destination outside 209.165.201.27 2055

Log all events between hosts 209.165.200.224 and hosts 209.165.201.224 to 209.165.200.230, and log all other events to 209.165.201.29:

hostname (config)# access-list flow_export_acl permit ip host 209.165.200.224 host 
209.165.201.224

hostname (config)# class-map flow_export_class

hostname (config-cmap)# match access-list flow_export_acl

hostname (config)# policy-map flow_export_policy

hostname (config-pmap)# class flow_export_class

hostname (config-pmap-c)# flow-export event-type all destination 209.165.200.230

hostname (config-pmap)# class class-default

hostname (config-pmap-c)# flow-export event-type all destination 209.165.201.29

hostname (config)# service-policy flow_export_policy global

Log flow-create events to 209.165.200.230, flow-teardown events to 209.165.201.29, and flow-denied events to 209.165.201.27:

hostname (config)# policy-map flow_export_policy

hostname (config-pmap)# class class-default

hostname (config-pmap-c)# flow-export event-type flow-creation destination 209.165.200.230

hostname (config-pmap-c)# flow-export event-type flow-teardown destination 209.165.201.29

hostname (config-pmap-c)# flow-export event-type flow-denied destination 209.165.201.27

hostname (config)# service-policy flow_export_policy global

Log flow-create events between hosts 209.165.200.224 and 209.165.200.230 to 209.165.201.29, and log all flow-denied events to 209.165.201.27:

hostname (config)# access-list flow_export_acl permit ip host 209.165.200.224 host 
209.165.200.230

hostname (config)# class-map flow_export_class

hostname (config)# match access-list flow_export_acl

hostname (config)# policy-map flow_export_policy

hostname (config-pmap)# class flow_export_class

hostname (config-pmap-c)# flow-export event-type flow-creation destination 209.165.200.29

hostname (config-pmap-c)# flow-export event-type flow-denied destination 209.165.201.27

hostname (config-pmap)# class class-default

hostname (config-pmap-c)# flow-export event-type flow-denied destination 209.165.201.27

hostname (config)# service-policy flow_export_policy global

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Note You must enter the following command:

hostname (config-pmap-c)# flow-export event-type flow-denied destination 209.165.201.27

for flow_export_acl, because traffic is not checked after the first match, and you must explicitly define the action to log flow-denied events that match flow_export_acl.

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Log all traffic except traffic between hosts 209.165.201.27 and 209.165.201.50 to 209.165.201.27:

hostname (config)# access-list flow_export_acl deny ip host 209.165.201.30 host 
209.165.201.50

hostname (config)# access-list flow_export_acl permit ip any any

hostname (config)# class-map flow_export_class

hostname (config-cmap)# match access-list flow_export_acl

hostname (config)# policy-map flow_export_policy

hostname (config-pmap)# class flow_export_class

hostname (config-pmap-c)# flow-export event-type all destination 209.165.201.27

hostname (config)# service-policy flow_export_policy global

Additional References

For additional information related to implementing NSEL, see the following sections:

•Related Documents

•RFCs

Related Documents

Related Topic	Document Title
Using NSEL and Syslog Messages	Cisco ASA 5500 Series System Log Messages
Information about the implementation of NSEL on the ASA	Implementation Note for NetFlow Collectors

RFCs

RFC	Title
3954	Cisco Systems NetFlow Services Export Version 9

Feature History for NSEL

Table 75-2 lists the release history for this feature.

Table 75-2 Feature History for NSEL 

Feature Name	Release	Feature Information
NetFlow	8.1(1)	The NetFlow feature enhances the ASA logging capabilities by logging flow-based events through the NetFlow protocol. NetFlow Version 9 services are used to export information about the progression of a flow from start to finish. The NetFlow implementation exports records that indicate significant events in the life of a flow. This implementation is different from traditional NetFlow, which exports data about flows at regular intervals. The NetFlow module also exports records about flows that are denied by access lists. You can configure an ASA 5580 to send the following events using NetFlow: flow create, flow teardown, and flow denied (only flows denied by ACLs are reported). The following commands were introduced: clear flow-export counters, flow-export enable, flow-export destination, flow-export template timeout-rate, logging flow-export syslogs enable | disable, show flow-export counters, show logging flow-export-syslogs
NetFlow Filtering	8.1(2)	You can filter NetFlow events based on traffic and event-type, and then send records to different collectors. For example, you can log all flow-create events to one collector, and log flow-denied events to a different collector. The following commands were modified: class , class-map, flow-export event-type destination, match access-list, policy-map, service-policy For short-lived flows, NetFlow collectors benefit from processing a single event instead of two events: flow create and flow teardown. You can configure a delay before sending the flow-create event. If the flow is torn down before the timer expires, only the flow teardown event is sent. The teardown event includes all information regarding the flow; no loss of information occurs. The flow-export delay flow-create command was introduced:
NSEL	8.2(1)	The NetFlow feature has been ported to all ASA 5500 series ASAs.