[nsp] Re: Per VLAN Stats on MSFC2 - Complaints from the Field

[Anthony Cennami]

If you want to bill accurately, bill off the Layer 2 ports; that's what 
is always churning the traffic.  I've not looked at the accuracy on a 
scientific level, but I've never found what I believed to be a serious 
discrepency when billing/polling the physical ports.

The reporting of the Layer 2 and 3 devices, virtual or otherwise appears 
to be correct; I argue that Cisco attempting to 'populate' the SVI 
counters with information they are actually not seeing would be 
'breaking' the implementation.  Remember folks, we're talking about 
multi layer switching/routing here; the SVI isn't processing all of the 
traffic and should not lie and say that it is.


Hudson Delbert J Contr 61 CS/SCBN wrote:

> cisco long ago made the decision that counting packets was NOT as important
> processing them. i've seen this thread in discussions about IOS since
> Version
> 9. they arent going to change the methodology right now because we need to
> bill off 
> of it. why use the overhead involved with passing info about L2 to L3 
> if 'train is still moving the cattle'. who cares?
> 
> 
> ~v/r
> Del Hudson
> 61CS/SCBN - LAAFB NCC
> Network Architecture & Engineering Group
> delbert.hudson at losangeles.af.mil
> 
> 
> 
> -----Original Message-----
> From: Gert Doering [mailto:gert at greenie.muc.de]
> Sent: Thursday, November 20, 2003 1:43 PM
> To: Anthony Cennami
> Cc: Nanog Mailing list; Robert A. Hayden; cisco-nsp at puck.nether.net
> Subject: Re: [nsp] Re: Per VLAN Stats on MSFC2 - Complaints from the
> Field
> 
> 
> Hi,
> 
> On Thu, Nov 20, 2003 at 12:52:02PM -0500, Anthony Cennami wrote:
> 
>>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 is all nice and shiny, but having shortcuts doesn't mean "the L2
> fabric can't export the resulting numbers up to the L3 brain".
> 
> They just botched it.  Counters and Cisco boxes seem to be fundamentally
> incompatible.
> 
> gert