So I stumbled upon the ip flow-top-talkers feature and attempted to configure it on a 3560-X running 12.2(58)SE2. It allowed me to configure this:
ip flow-top-talkers
top 5
sort-by bytes
cache-timeout 60000
Then on the interface I am interested in:
interface GigabitEthernet0/21
ip flow ingress
Which results is (drum roll please....)
Switch#show ip flow top
% Cache is empty
No joy. So I checked the config guide for unsupported commands, these are not listed.
Then I thought maybe it had to be on a layer 3 interface (g0/21 is layer 2) so I did "ip flow ingress" on an SVI, same results.
So then I checked feature navigatore for "Flexible Netflow - Top N Talkers Support". 12.2SE is not listed, but 15.0(2)SE is.
Questions:
- Is the existence of the commands in 12.2(58)SE just an oversight? Functionality seems to almost be there, just not quite.
- Does neflow need to be enabled on a layer 3 interface or will it work on layer 2 (assuming platform support of course)
Thanks,
-Jeff
Flexible NetFlow is supported only on the Catalyst 3750-X and 3560-X switch running the IP base or IP services feature set and equipped with the network services module. It is not supported on switches running the NPE or the LAN base image. 
