MS NetFlow and Encrypted Traffic Analytics

Overview 

Starting with CS15+ all Catalyst based (MS390/9300) have support for Network Based Application Recognition (NBAR) Netflow v10 (IPFIX) for IPv4 and IPv6 traffic, as well as Encrypted Traffic Analytics (ETA) flow export for use with NetFlow analyzers like Cisco's Secure Network Analytics (formerly Stealthwatch Enterprise and Cloud). This enables organizations to export incredibly granular flows of any traffic through a supported switch whether flowing east, west, north, or southbound. The addition of Encrypted Traffic Analytics allows for an organization to also correlate cryptographic standards as a means to identify security issues in protocols used locally, validation of security audits for compliance requirements, and the ability to fingerprint traffic without performing MiTM decryption. This is incredibly useful for products, like Cisco Secure Network Analytics and Cisco XDR, to perform fingerprinting of potential security events in the network such as encrypted malware and botnet activity. 

Features 

Flow recording configurations are implemented for both IPv4 and IPv6 by default. When the feature is enabled, every interface will collect flow records in both the input and output directions as per the AVC NetFlow specification in the UADP ASIC. This means that all traffic will be captured and exported to the specified NetFlow collector. There is support for up to 1x exporter configured per-network. 

Encrypted Traffic Analytics (ETA) support when configured is also enabled on every interface on every switch in the network that supports the feature and is configured correctly. This configuration enables Cisco's ETA functionality. For further information, read more about it here: Cisco Encrypted Traffic Analytics

Requirements

Hardware:

• MS390 (all models for AVC NetFlow + ETA)
• 9300/X/L-M (all models for AVC NetFlow + ETA)
• 9200/L-M (only supports AVC NetFlow)

Software:

• CS 15.X and later or Cloud Native IOS XE 17.15+

Licensing:

• Advanced Licensing

Configuration:

• L3 SVI configured on exporting switch/stack (this is default on cloud native IOS XE 17.15+)
• Collector that is reachable via L3 SVI

Configuration 

NetFlow and ETA configuration are broken down into a few steps:

1. Deploy NetFlow and ETA configurations under Network-wide > General where you will provide the NetFlow collector port and IP. This configuration is shared with any MXs deployed in the network. Optionally, you can enable Encrypted Traffic Analytics (ETA) and provide the UDP port for those ETA flow records to be shipped to. By default, these records are expected to be exported to the same flow collector. 
    
2. For NetFlow to work on Layer-2 switches in the initial release, the switch is required to have an SVI created for routing of the NetFlow traffic. This is due to ASIC forwarding functions and thus must be a separate IP address from the management IP that is used to communicate with dashboard. This does allow for NetFlow traffic to take an alternative path from management but must not be confused with Alternate Management Interface which is a separate feature for RADIUS, SNMP, and Syslog traffic that is outlined here: Alternate Management Interface on MS Devices
   1. This can be performed by navigating to Switch > Routing & DHCP and creating an SVI for the switch or switch stack to leverage for NetFlow and optionally ETA forwarding as well. Once the SVI is created, the traffic will egress via the data-plane forwarding table. 

Technical Breakdown 

NetFlow and ETA are enabled on every port on the switch or switch stack as long as the switches are supported and properly configured in the network as outlined above. This means that all traffic that flows through the switch will be recorded and exported as a flow record for further inspection by a central analysis tool. For customers that require NetFlow and/or ETA to be exported to more than one destination, a product like Cisco's Telemetry Broker or Secure Network Analytics UDP Director (Stealthwatch UDP Director) can be utilized for flow duplication and re-routing. 

The NetFlow recorder configurations are very granular and cover the following fields for both IPv4 and IPv6:

Troubleshooting 

A simple means to troubleshoot flow export would be to grab a packet capture on the uplink port and filtering in Wireshark for the UDP ports for ETA and NetFlow. This can be done by going to Network-wide > Packet capture (intelligent capture), select the switch in question, populate the uplink port, and select download for Wireshark. A 60 second capture should be sufficient in capturing some flow traffic if there are more than a few active clients behind the switch. 

Example: 

The following filter/s are handy:

cflow || udp.port == {netflow port} || udp.port == {eta port}

Example packet capture: