Catalyst 6500 Release 12.2SXF and Rebuilds Software Configuration Guide

Configuring NetFlow

This chapter describes how to configure NetFlow statistics collection on the Catalyst 6500 series switches.

Note For complete syntax and usage information for the commands used in this chapter, refer to this publication:

http://www.cisco.com/en/US/docs/ios/netflow/command/reference/nf_book.html

This chapter contains the following sections:

•Understanding NetFlow

•Default NetFlow Configuration

•NetFlow Configuration Guidelines and Restrictions

•Configuring NetFlow

Tip For additional information about Cisco Catalyst 6500 Series Switches (including configuration examples and troubleshooting information), see the documents listed on this page:

http://www.cisco.com/en/US/products/hw/switches/ps708/tsd_products_support_series_home.html

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Understanding NetFlow

These sections describe how NetFlow works:

•NetFlow Overview

•NetFlow on the MSFC

•NetFlow on the PFC

NetFlow Overview

The NetFlow feature collects traffic statistics about the packets that flow through the switch and stores the statistics in the NetFlow table. The NetFlow table on the MSFC captures statistics for flows routed in software and the NetFlow table on the PFC (and on each DFC) captures statistics for flows routed in hardware.

Several features use the NetFlow table: features such as network address translation (NAT) use NetFlow to modify the forwarding result; other features (such as QOS microflow policing) use the statistics from the NetFlow table to apply QOS policies. The NetFlow Data Export (NDE) feature provides the ability to export the statistics to an external device (called a NetFlow collector).

In PFC3A mode, NetFlow collects statistics only for routed traffic. With a PFC3B or PFC3BXL, you can configure NetFlow to collect statistics for both routed and bridged traffic. Netflow for bridged traffic requires Release 12.2(18)SXE or later.

Collecting and exporting a large volume of statistics can significantly impact supervisor engine and MSFC processor usage, so NetFlow provides configuration options to control the volume of statistics. These options include the following:

•NetFlow flow masks determine the granularity of the flows to be measured. Very specific flow masks generate a large number of NetFlow table entries and a large volume of statistics to export. Less specific flow masks aggregate the traffic statistics into fewer NetFlow table entries and generate a lower volume of statistics.

•Sampled NetFlow exports data for a subset of traffic in a flow, which can greatly reduce the volume of statistics exported. Sampled NetFlow does not reduce the volume of statistics collected.

•NetFlow aggregation merges the collected statistics prior to export. Aggregation reduces the volume of records exported, but does not reduce the volume of statistics collected. Note that NetFlow aggregation increases switch CPU utilization and reduces the data available at the collector. NetFlow aggregation uses NetFlow version 8.

NetFlow defines three configurable timers to identify stale flows that can be deleted from the table. NetFlow deletes the stale entries to free up table space for new entries.

NetFlow on the MSFC

The NetFlow table on the MSFC captures statistics for flows routed in software. NetFlow on the MSFC supports NetFlow aggregation. For information about the NetFlow aggregation schemes, refer to the following document:

Cisco IOS NetFlow Configuration Guide.

For information about configuring NetFlow aggregation on the MSFC, refer to the following document:

Cisco IOS NetFlow Configuration Guide.

NetFlow on the MSFC supports ToS-based router aggregation, described in this document:

Cisco IOS NetFlow Configuration Guide.

Release 12.2(18)SXF and later releases support NetFlow for multicast IP. For additional information about NetFlow for multicast IP, refer to the NetFlow Multicast Support document, available in this document:

Cisco IOS NetFlow Configuration Guide.

The NetFlow Multicast Support document contains a prerequisite specifying that you need to configure multicast fast switching or multicast distributed fast switching (MDFS). However, this prerequisite does not apply when configuring NetFlow multicast support with Release 12.2(18)SXF and later releases.

NetFlow on the PFC

The NetFlow table on the PFC captures statistics for flows routed in hardware. The PFC supports sampled NetFlow and NetFlow aggregation. The PFC does not support NetFlow ToS-based router aggregation.

These sections describe NetFlow on the PFC in more detail:

•Flow Masks

•Flow Mask Conflicts

Flow Masks

A flow is a unidirectional stream of packets between a given source and a given destination. A flow mask specifies the fields in the incoming packet that NetFlow uses to identify the flow. NetFlow gathers statistics for each flow defined by the flow mask.

The PFC supports the following flow masks:

•source-only—A less-specific flow mask. The PFC maintains one entry for each source IP address. Statistics for all flows from a given source IP address aggregate into this entry.

•destination—A less-specific flow mask. The PFC maintains one entry for each destination IP address. Statistics for all flows to a given destination IP address aggregate into this entry.

•destination-source—A more-specific flow mask. The PFC maintains one entry for each source and destination IP address pair. Statistics for all flows between the same source IP address and destination IP address aggregate into this entry.

•destination-source-interface—A more-specific flow mask. Adds the source VLAN SNMP ifIndex to the information in the destination-source flow mask.

•full—A more-specific flow mask. The PFC creates and maintains a separate table entry for each IP flow. A full entry includes the source IP address, destination IP address, protocol, and protocol ports.

•full-interface—The most-specific flow mask. Adds the source VLAN SNMP ifIndex to the information in the full-flow mask.

The flow mask determines the granularity of the statistics gathered, which controls the size of the NetFlow table. The less-specific flow masks result in fewer entries in the NetFlow table and the most-specific flow masks result in the most NetFlow entries.

For example, if the flow mask is set to source-only, the NetFlow table contains only one entry per source IP address. The statistics for all flows from a given source are accumulated in the one entry. However, if the flow mask is configured as full, the NetFlow table contains one entry per full flow. Many entries may exist per source IP address, so the NetFlow table can become very large. See the "NetFlow Configuration Guidelines and Restrictions" section for information about NetFlow table capacity.

Flow Mask Conflicts

Several features use the NetFlow table. Table 50-1 lists the flow mask requirements for each feature.

Because of the variety of feature requirements, potential flow mask conflicts can occur. Note the following flow mask constraints:

•With a PFC2, all features share the same global flow mask.

•With a PFC3, all features must share the same limited set of flow masks.

•The PFC can apply only one flow mask to each packet lookup.

The Feature Manager software in the MSFC is responsible for resolving feature conflicts. The Feature Manager's main strategy is to select a common flow mask that satisfies all the configured NetFlow features.

However, the Feature Manager may not find a common flow mask for the configured features, because some features have very specific requirements for the flow mask. To resolve the feature conflict, Feature Manager software may direct one of the features to be processed in software on the MSFC.

In the extreme case, Feature Manager software gives priority to the feature that is configured first and rejects configuration requests for subsequent features. When you attempt to configure a subsequent feature that the Feature Manager cannot accommodate, you receive a failure message at the CLI.

Follow these guidelines to avoid problems with feature conflicts:

•Configure your highest priority features first. If an unresolvable conflict occurs, your lower priority features may be blocked.

•If possible, configure features only on the interfaces where the feature is required.

•Pay attention to response messages. If the Feature Manager turns off hardware assist for a feature, you need to ensure that feature processing does not overload the RP processor.

Note the following specific feature conflicts:

•CBAC requires the full flow mask, and is given priority over other flow-based features. If a flow mask conflict occurs, the other flow-based features are processed in the MSFC.

•In general, NDE is flexible because you configure the minimum flow mask. If you have configured other flow-based features, Feature Manager software may set a more specific flow mask to meet all the feature requirements.

•Sampled NetFlow requires the dest-source-interface flow mask (PFC2) or full-interface flow mask (PFC2 and PFC3). This may cause conflict with other flow-based features on the same interface.

•NDE conflicts with QoS. NDE and QoS microflow policing cannot be configured on the same interface.

•If NAT is configured on a Layer 3 interface with any feature that uses dynamic ACEs (for example, Web Proxy Authentication or NAC Layer 3 IP validation), trailing fragments may not be NAT translated correctly if NAT is configured for overload. For systems equipped with a PFC3B or PFC3BXL, you can use the mls ip nat netflow-frag-l4-zero command to ensure that NAT functions correctly in this case.

Default NetFlow Configuration

Table 50-2 shows the default NetFlow configuration.

NetFlow Configuration Guidelines and Restrictions

When configuring NetFlow, follow these guidelines and restrictions:

•The CEF table (and not the NetFlow table) implements Layer 3 switching in hardware.

•In PFC3B or PFC3BXL mode with Release 12.2(18)SXE and later releases, NetFlow supports bridged IP traffic. PFC3A mode does not support NetFlow bridged IP traffic.

•In Release 12.2(18)SXF and later releases, NetFlow supports multicast IP traffic.

•No statistics are available for flows that are switched when the NetFlow table is full.

•If the NetFlow table utilization exceeds the recommended utilization levels, there is an increased probability that there will be insufficient room to store statistics. Table 50-3 lists the recommended maximum utilization levels.

Configuring NetFlow

These sections describe how to configure NetFlow:

•Configuring NetFlow on the PFC

•Configuring NetFlow on the MSFC

Note When you configure NAT on an interface, the PFC sends all fragmented packets to the MSFC to be processed in software. (CSCdz51590)

Configuring NetFlow on the PFC

These sections describe how to configure NetFlow statistics collection on the PFC:

•NetFlow PFC Commands Summary

•Enabling NetFlow on the PFC

•Setting the Minimum IP MLS Flow Mask

•Configuring the MLS Aging Time

•Configuring NetFlow Aggregation on the PFC

•Enabling NetFlow for Ingress-Bridged IP Traffic

•Enabling NetFlow for Multicast IP Traffic

•Displaying PFC Netflow Information

NetFlow PFC Commands Summary

Table 50-4 shows a summary of the NetFlow commands available on the PFC.

Note•When you configure NetFlow aggregation on the MSFC, it is enabled automatically on the PFC.

•When you configure NetFlow for Layer 2 traffic on the MSFC, it is enabled automatically on the PFC.

•When you configure multicast NetFlow on the MSFC, it is enabled automatically on the PFC. Multicast NetFLow is supported in Release 12.2(18)SXF and later releases.

Enabling NetFlow on the PFC

To enable NetFlow statistics collection on the PFC, perform this task:

This example shows how to disable NetFlow statistics collection on the PFC (the default setting is enabled):

Router(config)# no mls netflow 

Setting the Minimum IP MLS Flow Mask

You can set the minimum specificity of the flow mask for the NetFlow table on the PFC. The actual flow mask may be more specific than the level configured in the mls flow ip command, if other configured features need a more specific flow mask (see the "Flow Mask Conflicts" section).

To set the minimum IP MLS flow mask, perform this task:

This example shows how to set the minimum IP MLS flow mask:

Router(config)# mls flow ip destination 

To display the IP MLS flow mask configuration, perform this task:

This example shows how to display the MLS flow mask configuration:

Router# show mls netflow flowmask 

current ip flowmask for unicast: destination address

Router#

Configuring the MLS Aging Time

The MLS aging time (default 300 seconds) applies to all NetFlow table entries. You can configure the normal aging time in the range of 32 to 4092 seconds. Flows can age as much as 4 seconds sooner or later than the configured interval. On average, flows age within 2 seconds of the configured value.

Other events might cause MLS entries to be purged, such as routing changes or a change in link state.

Note If the number of MLS entries exceeds the recommended utilization (see the "NetFlow Configuration Guidelines and Restrictions" section), only adjacency statistics might be available for some flows.

To keep the NetFlow table size below the recommended utilization, enable the following parameters when using the mls aging command:

•normal—Configures an inactivity timer. If no packets are received on a flow within the duration of the timer, the flow entry is deleted from the table.

•fast aging—Configures an efficient process to age out entries created for flows that only switch a few packets, and then are never used again. The fast aging parameter uses the time keyword value to check if at least the threshold keyword value of packets have been switched for each flow. If a flow has not switched the threshold number of packets during the time interval, then the entry is aged out.

•long—Configures entries for deletion that have been active for the specified value even if the entry is still in use. Long aging is used to prevent counter wraparound, which can cause inaccurate statistics.

A typical table entry that is removed by fast aging is the entry for flows to and from a Domain Name Server (DNS) or TFTP server.

If you need to enable MLS fast aging time, initially set the value to 128 seconds. If the size of the NetFlow table continues to grow over the recommended utilization, decrease the setting until the table size stays below the recommended utilization. If the table continues to grow over the recommended utilization, decrease the normal MLS aging time.

To configure the MLS aging time, perform this task:

This example displays how to configure the MLS aging time:

Router# configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

Router(config)# mls aging fast threshold 64 time 30

To display the MLS aging-time configuration, perform this task:

This example shows how to display the MLS aging-time configuration:

Router# show mls netflow aging 

enable timeout packet threshold 

------ ------- ---------------- 

normal aging true 300 N/A 

fast aging true 32 100 

long aging true 900 N/A 

Configuring NetFlow Aggregation on the PFC

NetFlow Aggregation is configured automatically on the PFC and DFCs when you configure NetFlow Aggregation on the MSFC (see the "Configuring NetFlow Aggregation on the MSFC" section).

To display NetFlow Aggregation information for the PFC or DFCs, perform this task:

Note The PFC and DFCs do not support NetFlow ToS-based router Aggregation.

This example shows how to display the NetFlow Aggregation cache information:

Router# show ip cache flow aggregation destination-prefix module 1 

IPFLOW_DST_PREFIX_AGGREGATION records and statistics for module :1 

IP Flow Switching Cache, 278544 bytes 

2 active, 4094 inactive, 6 added 

236 ager polls, 0 flow alloc failures 

Active flows timeout in 30 minutes 

Inactive flows timeout in 15 seconds 

Dst If Dst Prefix Msk AS Flows Pkts B/Pk Active 

Gi7/9 9.1.0.0 /16 0 3003 12M 64 1699.8 

Gi7/10 11.1.0.0 /16 0 3000 9873K 64 1699.8 

Router#

This example shows how to display the NetFlow Aggregation flow mask information:

Router# show mls netflow aggregation flowmask 

 Current flowmask set for netflow aggregation : Vlan Full Flow

 Netflow aggregations configured/enabled :

        AS Aggregation

        PROTOCOL-PORT Aggregation

        SOURCE-PREFIX Aggregation

        DESTINATION-PREFIX Aggregation

Router#

Enabling NetFlow for Ingress-Bridged IP Traffic

NetFlow for ingress-bridged IP traffic on the PFC is enabled when you configure NetFlow for ingress-bridged IP traffic on the MSFC. See the "Enabling NetFlow for Ingress-Bridged IP Traffic" section.

Enabling NetFlow for Multicast IP Traffic

NetFlow for multicast IP traffic on the PFC is enabled when you configure NetFlow for multicast IP traffic on the MSFC. NetFlow for multicast IP traffic is supported in Release 12.2(18)SXF and later releases.

For additional information, see the "Enabling NetFlow for Multicast IP Traffic" section.

Displaying PFC Netflow Information

To display information about NetFlow on the PFC, use the following command:

Configuring NetFlow on the MSFC

These sections describe how to configure NetFlow on the MSFC:

•Summary of NetFlow Commands on the MSFC

•Enabling NetFlow on the MSFC

•Configuring NetFlow Aggregation on the MSFC

•Enabling NetFlow for Ingress-Bridged IP Traffic

•Enabling NetFlow for Multicast IP Traffic

Summary of NetFlow Commands on the MSFC

Table 50-5 shows the NetFlow commands available on the MSFC.

Enabling NetFlow on the MSFC

To enable NetFlow on the MSFC, perform this task for each Layer 3 interface from which you want NetFlow:

In Release 12.2(18)SXF and later releases, you need to enter the ip flow ingress command to enable NetFlow for the interface. In releases prior to Release 12.2(18)SXF, NetFlow is enabled by default.

Configuring NetFlow Aggregation on the MSFC

For information on configuring NetFlow aggregation on the MSFC, refer to the following documentation:

Cisco IOS netFlow Configuration Guide.

For information on configuring NetFlow ToS-based router aggregation on the MSFC, refer to the following documentation:

Cisco IOS netFlow Configuration Guide.

Note•When you configure NetFlow aggregation on the MSFC, it is configured automatically on the PFC and DFCs (see the "Configuring NetFlow Aggregation on the PFC" section).

•The PFC and DFCs do not support NetFlow ToS-based router aggregation.

Enabling NetFlow for Ingress-Bridged IP Traffic

In PFC3B or PFC3BXL mode with Release 12.2(18)SXE and later releases, NetFlow supports ingress-bridged IP traffic. PFC3A mode does not support NetFlow for bridged IP traffic.

Note•When you enable NetFlow for ingress-bridged IP traffic, the statistics are available to the Sampled NetFlow feature (see the "NetFlow Sampling" section).

•To enable NetFlow for bridged IP traffic on a VLAN, you must create a corresponding VLAN interface, assign it an IP address, and enter the no shutdown command to bring up the interface.

To enable NetFlow for ingress-bridged IP traffic in VLANs, perform this task:

This example shows how to enable NetFlow for ingress-bridged IP traffic in VLAN 200:

Router# configure terminal 

Enter configuration commands, one per line.  End with CNTL/Z.

Router(config)# ip flow ingress layer2-switched vlan 200 

Enabling NetFlow for Multicast IP Traffic

Release 12.2(18)SXF and later releases support NetFlow for multicast IP. To enable NetFlow for multicast IP, perform this task:

:

For additional information about NetFlow for multicast IP, refer to the NetFlow Multicast Support documentation, available in the following document:

Cisco IOS NetFlow Configuration Guide.

The NetFlow Multicast Support document contains a prerequisite specifying that you need to configure multicast fast switching or multicast distributed fast switching (MDFS). However, this prerequisite does not apply when configuring NetFlow multicast support with Release 12.2(18)SXF and later 12.2SX releases.

Tip For additional information about Cisco Catalyst 6500 Series Switches (including configuration examples and troubleshooting information), see the documents listed on this page:

http://www.cisco.com/en/US/products/hw/switches/ps708/tsd_products_support_series_home.html

Participate in the Technical Documentation Ideas forum