NetFlow v9 is gaining market share, albeit slowly, and isn’t as deterministic as NetFlow v5. NetFlow v9 templates are the big differentiators here. Read what happens when WireShark doesn’t receive a template before receiving the NetFlow v9 packets.
Anyway, the NetFlow v9 packet format is dynamic. Because of this, NetFlow v9 templates must be sent periodically to tell the NetFlow collector the format of the flows being exported. I fired up WireShark and caught a template below. Nothing like some NetFlow fishing: