Fun with Router IP Traffic Export and NSM
The BasicsI finally got around to setting up Security Onion (the best network security monitoring package available) to monitor my home network, only to discover that my Cisco 891 router doesn't support support the right form of SPAN. Here's how I worked around it. The topology looks like this:
The 891 router has an integrated 8-port switch module, so the simple case would have been a traditional SPAN setup; something like this:
! vlan 10 is the user VLAN
monitor session 1 source interface vlan 10
monitor session 1 destination interface FastEthernet0
with the server's monitoring NIC connected to FastEthernet0.
The problem is that the 891 doesn't support using a VLAN as a source interface, and because of the way the embedded WAP works, a physical source interface won't work either. Hence, I turned to an obscure feature that's helped me occasionally in the past: Router IP Traffic Export. This is a feature for IOS software platforms that enables you to enable SPAN-like functions for almost any source interface.
The configuration looks like this:
ip traffic-export profile RITE_MIRROR
interface FastEthernet0
bidirectional
mac-address 6805.ca21.2ddd
interface Vlan10
ip traffic-export apply RITE_MIRROR
This takes all traffic routed across Continue reading




