[mrtg] Help graphing MAC address count from Cisco switch

Fred Weston fweston at gmail.com
Sat Mar 19 19:24:11 CET 2016

Thanks for the suggestion, that has me on the right path but I'm still
having some trouble extracting the specific info I'm looking for.

CnTWaLK. at

Gets me a count of the MAC addresses in the switch's CAM table, but
I'm trying to graph MAC addresses by VLAN so I want to create a
separate graph for each VLAN and for each of those graphs, I only want
to show the number of MAC addresses in the switch's CAM table for that
specific VLAN.

If I run this snmpwalk command:
snmpwalk -v 2c -c public at 10 .

It returns info only for VLAN 10.

Notice above that I'm using "<snmp_community>@<vlan_number>" followed
by a space, then the SNMP host's IP address.  The problem is I can't
seem to figure out how to turn this into a target line in MRTG where I
can specify that I only want information for a certain VLAN.

On my target line in MRTG, I've tried various permutations of adding
the VLAN # but none have seemed to work.

Any suggestions on how I could accomplish this?


On Fri, Mar 18, 2016 at 10:20 PM, Alex van den Bogaerdt
<alex at vandenbogaerdt.nl> wrote:
>> Hello,
>> I'm trying to create a graph showing the # of devices connected to a
>> particular network.  The simplest way I can think of to do so is to
>> grab the # of MAC addresses in the CAM table for that particular VLAN
>> from the L3 switch which is the default gateway for the network.
> [...]
>> I found this command online, and it returns an integer which
>> represents the # of MAC addresses the switch knows about for the
>> particular VLAN in question (VLAN 40 as shown below):
>> snmpwalk -v 2c -c public at 30 . |wc -l
> I found this while reading the documentation:
> Counted SNMP Walk
> You probably want to use that instead of the external monitoring script.

More information about the mrtg mailing list