[c-nsp] SNMP Usage on Switchports vs. Router SubInterfaces

TJ Easter tjeaster at gmail.com
Wed Jan 11 20:01:14 EST 2006


Rick,
    I've been using a homegrown mix of rrdtool and perl's SNMP module
to poll sub-ifaces on 75xx and 76xx routers for quite some time.  
Can't say that I've ever seen any inconsistencies.

   Also, if I understand your scenario correctly, then no, the frames
(L2) would never make it to the 75xx iface as the switch would handle
the traffic.   If you want per-port stats, poll the switch.  If you
want internet usage, poll the 7200.

Regards,
TJ Easter

On 1/10/06, Rick Kunkel <kunkel at w-link.net> wrote:
> Hello all,
>
> We've currently got a bunch of machines hooked up to several 3550 and 2924
> switches.  In most cases, each machine is owned by a different customer,
> is connected to a different switchport, and is in it's own VLAN, connected
> via an 802.1q trunk to a 7200 series router, which has a bunch of
> GigaBitEthernet subinterfaces, one for each VLAN.  We're using RTG to
> track usage through SNMP on the switchports.  The intent is to capture the
> amount of traffic to the Internet they're using.  In the occasional case
> where a customer has more than one switchport and they're passing a bunch
> of traffic between these switchports, AFAIK our usage info is pretty much
> useless.
>
> My questions are these:
>
> 1.  If I collect SNMP data on the GigabitEthernet subinterfaces of the
> 7200 series router, will that more accurately reflect what I'm trying to
> get?  Or, in other words, will it at least exclude the traffic that is
> passing from switchport to switchport, because -- I think -- this traffic
> never makes it up to the router's interface?
>
> 2.  Is there a better way to track this data?  How are others doing things
> in cimilar situations?
>
> 3.  Related to above:  Should I be using NetFlow instead, and if so, what
> open source tools are available for dealing wit this data?
>
> Thanks much!
>
> Rick Kunkel
>
>
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