Most network engineers who are familiar with RMON know to use the “alarms” and “events” to monitor things like the CPU loading hitting a certain threshold or looking for the number of incoming packets on an interface. Cisco Catalyst switches support some RMON features that allow you to collect more information about packets that arrive on your interfaces. If you want to enable this then you have two options:
- Native Mode (Analyze packets that are destined for your interface).
- Promiscuous Mode (Analyze all packets that you encounter on the segment).
You can enable this for switchports (layer 2) or routed ports (layer 3) but it’s impossible to enable it on SVI (switch virtual interface) interfaces. Here’s an example how you can enable it on your Catalyst switch:
Switch(config)#interface fastEthernet 0/1 Switch(config-if)#rmon ? collection Configure Remote Monitoring Collection on an interface native Monitor the interface in native mode promiscuous Monitor the interface in promiscuous mode
First you need to decide whether you want to use the native or promiscuous mode. I’ll select promiscuous:
Second step is to configure how often and how much statistics we want to collect:
Switch(config-if)#rmon collection history 1 ? buckets Requested buckets of intervals. Default is 50 buckets interval Interval to sample data for each bucket. Default is 1800 seconds owner Set the owner of this RMON collection <cr>
The “1” is the RMON collection control index, you can pick any value you like. By default RMON will sample data each 1800 seconds..this is a little too long for my example so I’ll reduce it to 5 seconds:
Switch(config-if)#rmon collection history 1 interval 5
Now let’s see if my switch has collected anything: