[mrtg] Re: Cisco VLAN Question

Fri Nov 30 23:16:50 MET 2001

Dave,

I am steady working on the same issue.  My understanding is that the asic is handling all of the vlan traffic, but the router only knows about the traffic if the asic does not have an entry in the fdb.  As of yet I am unable to find a way to query the asic.  I am a bit concerned about the overhead involved in using netflow as well.  Please let me know if you  have made any headway.  I think I might put up a website devoted to this issue until resolved.

Regards,

James McGovern Amann
Network Technician Lead
Georgia State University
UCCS / Network Planning 
PH: 404.651.1574
FX: 404.651.4669
PG: 404.476.7754
jamann at gsu.edu

>>> "Dave Williams" <dave_williams at eli.net> 11/19/01 04:25PM >>> 

There are a couple of issues to sort out first regarding how to get vlan 
statistics. First of all the Cisco 6000 switch family with integrated layer-3 
routing module (MSFCx), can run using native-mode or hybrid mode software. 
Native mode configurations have a separate Catalyst Supervisor software image, 
and a separate Cisoc IOS software image for the MSFC. Hybrid mode 
configurations integrate the layer-2 and layer-3 configuration functions into 
Cisco IOS. In hybrid mode the IOS image configures each port using IOS 
SwitchPort commands. In native mode the Catalyst Supervisor software 
configures the ethernet ports using set commands (vlan, port, etc.). So in 
native mode you can interrogate the supervisor's IP address for information 
about GigEthernet trunk utilization, or say a specific ethernet workstation 
port (using MRTG name probably works best for this). In hybrid mode you can 
interrogate individual ports or trunk links using the router's IP address and 
a specific interface number or perhaps MRTG's name function). Bottom line 
specific port statistics or port trunks statistics are easy to get MRTG to 
report against. 

Now for the vlan challenges, either native or hybrid does not seem to record 
total Vlan traffic. I'm not totally certain my understanding about this is 
complete, but I have a 6509 with Supervisor IA which have the integrated MSFC2 
and PFC functions. In my case the MSFC router routes new conversations (by 
destination, by combination of source and destination, or by combination of 
source, destination, and layer 4 port #;s depending on how you configure 
layer-3 switching) once and then caches in the PFC subsequent layer-3 packet 
flows. I am running Hybrid mode and so my router Vlan interface statistics 
only record initial routed packet flows. Subsequent flow conversations are 
handled by the PFC so the router does not record any traffic for layer-3 
switched packets. Normally my Vlan statistics would reach 2000-3000 pps. Now 
the router is only handling less than 5 pps. Almost all packets are switched 
at the speed of the 6509 backplane. 

As far as I can tell to get complete Vlan traffic statistics you need to 
configure NetFlow and periodically export data (based on Vlan subnetworks) to 
a NetFlow data collector. If anyone is doing this using scripts adapted to 
MRTG I'd be very interested. My previous 
inquiries to the MRTG mailing list did not generate any replies from folks 
doing this yet. I am working with Cisco to figure out how to go about getting 
this information in more detail with an eye towards MRTG integration. 

Harris wrote: 

> I have a Cisco 6506 with a 16 port gigabit module and a 48 port 10/100 
> module. The system is running as a layer 3 router. On the switch side 
> various ports are tied together into different VLANs. There are a total of 
> 13 different VLANs. On the router side each VLAN is given a router IP 
> port. when I run the cfgmaker software it rems out the VLAN interfaces. Is 
> there a way to configure mrtg to see the traffic going across the VLAN's 
> router ip? If this is not possible I would be happy with the gigabit 
> ports' traffic. I tried to do this on the switch side, but that did not 
> seem to work either. Any suggestions that can point me in the right 
> direction would be most appreciated. 
> 
> George Harris 
> Network Engineer 
> Northern Valley Regional High School 
> 
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