Per VLAN Stats on MSFC2 - Complaints from the Field

Anthony Cennami narziss at
Thu Nov 20 17:52:02 UTC 2003

This is because in 1996 you were likely not dealing with 'Switch 
Routers'; today's 'routers' perform some form of flow switching/caching, 
meaning once the traffic enters the VLAN routed interface and an 
appropriate path is found it is sent down the the Layer 2 fabric.  This 
can be circumvented by disabling MLS on your fabric, but will result in 
all of your packets being process switched, inherently increasing the 
CPU load of your MSFC/CPU.

Depending on your configuration, your SVI information can be coupled 
with the Layer 2 SNMP statistics (at least for I/O) to provide more 
accurate numbers.

I apologize if I have missed something, but I'm assuming this is what 
you're alluding to.


Anthony Cennami

Robert A. Hayden wrote:
> Hey all,
> This one is a weird one.  I apologize if this is a bit off topic.
> As everyone is probably aware, the Cisco 6500/7600 line is unable to
> provide per-vlan I/O statistics on routed interfaces (ie, a "show int vlan
> xxx" has meaningless numbers in the I/O and error fields at the end).  
> MIB tables also fail to provide meaningful data.  You CAN get some L2 VLAN
> data, but that doesn't help you when you need to know what's going through
> the router interface.
> We've be going around and around with the vendor for a while now about how
> this makes it pretty useless for traffic analysis, and even showed them
> the RFC that requires that the information be made available to call it a
> router.  Their latest tactic is to claim that "nobody else in the industry
> is concerned about this shortcoming".
> For us, we've been collecting routed interface stats going back all the 
> way to 1996 and with our new gear we've been sold we find that our graphs 
> are pretty empty and we get no reasonable information about how much 
> traffic is passing through the L3 interfaces.
> So, here's the question I have for anybody out there dealing with this 
> hardware.  Is this shortcoming an issue for how you run your network?  
> Have you asked Cisco to fix it?  My feeling is that a lot of people find 
> it to be an issue and simply accept it is yet another broken cisco thing.
> Please let me know privately.  I want to talk into our next meeting with
> some printed testimonials from "real people" that this box is plain
> broken.  Let me know as well if you don't want me to use your name and/or
> organization in my report.
> Thanks for your time.
> - Robert Hayden
> University of Wisconsin Madison

More information about the NANOG mailing list