NetFlow is a Cisco IOS application that provides statistics on packets flowing through the router. NetFlow is a primary network accounting and security technology.

Prerequisites for Configuring NetFlow and NetFlow Data Export

Before you enable NetFlow you must:

• Configure the router for IP routing
• Ensure that one of the following is enabled on your router, and on the interfaces that you want to configure NetFlow on
  • Cisco Express Forwarding (CEF)
  • distributed CEF
  • fast switching

Special notes for specific IOS versions:

• If your router is running a version of Cisco IOS prior to releases 12.2(14)S, 12.0(22)S, or 12.2(15)T the ip route-cache flow command is used to enable NetFlow on an interface.
• If your router is running Cisco IOS release 12.2(14)S, 12.0(22)S, 12.2(15)T, or later the ip flow ingress command is used to enable NetFlow on an interface.

To configure netflow, here are the steps:

router>enable
router# configure terminal
router(config)# interface interface-type interface-number
router(config-if)# ip flow {ingress | egress}
router(config-if)# end
router# copy run start

Repeat interface command on any others you want to see traffic statistics on.

Commands to verify Netflow configuration:

Router# show ip flow interface (shows which interfaces netflow is configured on)
Router# show ip cache flow (shows a summary of capture statistics)

Now that netflow is collecting, configure an export destination:

router>enable
router# configure terminal
router(config)# ip flow-export source interface-type interface-number
router(config)# ip flow-export destination ip address of collector source port <optional>
router(config)# ip flow-export version number

Command to verify Netflow data export

router# ip flow-export version