To clarify here are the scenarios I'm trying to understand:
1) 2 different routers with the same /30 WAN interface IPs -
2) 2 different routers with the same management IP address but different /30 WAN interface IPs
From what I can understand #1 is not an issue because you can set the netflow source to be an interface other than the WAN interface, avoiding having duplicate NetFlow sources in the collector.
#2 seems like it will clearly be an issue.
Anyone have any experience or theories to share?