03-15-2025 04:02 AM - edited 03-15-2025 04:04 AM
Hello, everyone.
I am studying NetFlow and here is my topology:
I started a ping from R2 to R1 and I configured the following on SW1:
Why doesn't SW1 register the flow (ignore the Total Flows set to 1, that was from a different config)? I've read some explanations on the internet which said that NetFlow won't capture anything on L2 ports? So is it not possible to capture local LAN/VLAN flows?
Thank you.
David
03-15-2025 04:44 AM
"Why doesn't SW1 register the flow . . . ?"
Most likely for the same reason "switch when you can, route when you must".
If you don't know the latter's reason, its forwarding performance.
BTW, and historically, on routers, a major feature of NetFlow was to increase a router's performance. On a switch, it would decrease its performance.
Today, a switch's performance wouldn't necessarily be impacted, but it would very likely increase its cost.
03-15-2025 05:54 AM
I am not sure in the Virtual environment, but the recent Cat 9K Model works.
May be try cat 9K v for testing (you may need good compute for the image - i have not tested).
03-15-2025 06:41 AM
". . . but the recent Cat 9K Model works."
I didn't know that but not too surprising as these current gen switches are also L3 and aren't particularly inexpensive.
I find it interesting how many previously only software features are now supported by hardware, often Cisco proprietary hardware.
03-15-2025 08:40 AM - edited 03-15-2025 08:41 AM
Hello @Mitrixsen ,
as noted by BB some platforms may support it but my guess is you need a special configuration for netflow to capture bridged traffic. I have seen it on Nexus 9000 series.
see
My understanding is that you can configure bridged netflow at broadcast domain layer.
on a physical layer 2 interface you can create a custom flow record that matches on IP and/or on MAC addresses or ethertype and it is supported only in ingress direction.
Hope to help
Giuseppe
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