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Home > Success Center > Netflow Traffic Analyzer (NTA) > Netflow data is unavailable on Cisco Nexus devices

Netflow data is unavailable on Cisco Nexus devices

Updated April 11, 2017

Overview

Netflow data is not available on some Cisco Nexus devices that are configured to use Netflow v5. Devices can still be configured but the use of Flexible Netflow is recommended. Data is not being processed because the interface index values do not match the values in the flow data and SNMP index values stored in the database when the device is discovered.

Environment

  • All NTA versions
  • Cisco Nexus devices configured using Netflow v5

Cause 

Flow data contains interface index value fields InputInt and OutputInt. These fields in Netflow v5 are 2 bytes and can only hold a maximum value of 65535. Netflow v9 on the other hand, uses 4 bytes and can hold a maximum value of 4294967295. Since v5 cannot hold the entire value, the InputInt and OutputInt fields are changed and do not match the interface index values in the database. The packets are then dropped since the values exported using v5 are changed and does not represent the matching SNMP interface index values.

This can be verified using a Wireshark capture and an SNMP walk to compare the interface index values.

Wireshark

InputIfIndex

OutputIfIndex

3096

200

3096

253

3096

253

3096

253

3096

151

3096

151

SNMP values when discovered

InterfaceIndex

151060481

151060499

151060628

151060631

151060640

151060641

151060667

151060680

Resolution

Change the Netflow configuration on the Cisco Nexus device to use Flexible Netflow instead of Netflow v5.

 

 

 

Last modified
20:40, 26 Apr 2017

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