Traffic billing - L2 encap to include or not?

Weber, Markus fvd at
Fri Jun 12 13:32:42 UTC 2009

We all have our billing systems for traffic (bought, downloaded or 
home made, volume based or usage).  We all got hit by fancy SNMP
bugs of various vendors and we all suffer from the fact, that SNMP
counters do not carry a time stamp, when they had been taken from
the ASICs, causing a slight derivation. [...]

Most systems (not the xflow based ones) do use IF-MIB::InOctets and
IF-MIB::OutOctets or their HC counter parts to retrieve the number
of transmitted bytes and do their calculation based on these numbers.

What would you expect these counters to return, esp. on Ethernet?
RFC2683 states 

      The definitions of ifInOctets and ifOutOctets (and similarly,
      ifHCInOctets and ifHCOutOctets) specify that their values include
      framing characters.  The media-specific MIB designer MUST specify
      any special conditions of the media concerning the inclusion of
      framing characters, especially with respect to frames with errors.

   The total number of octets transmitted out of/received on the
      interface, including framing characters."

So, is L2 encapsulation (e.g. Ethernet) considered as framing characters
or not?

Cisco does count them (looks like they also count the FCS), while 
Juniper does not (at least not on their routers) with above MIBs.
So who's right?

Which brings me to the question: How do others handle this? Do your
customers have to pay for the L2 encapsulation overhead or not? Does
your (special) G T&C address this? Does your system adjust the
numbers by adding/subtracting L2 enc overhead * number of transmitted
packets? Or do you just live with it as it is (and hope, your provider
uses J-counters to do their billing).

Oh, it's Friday ... Markus

PS1: And what about padding? IP packets could be smaller then the min
     ethernet frame size ... (think of some kind of DOS attacks) ...
PS2: Oh, maybe someone could check on J switches - would be nice to
     know ...
[E] Markus Weber <fvd at kpn.DE> [IRC] FvD [T] +49 69 96874-298 [F] -289
[KPN Eurorings B.V.   Darmstädter Landstraße 184   D-60598 Frankfurt]
[HRB56874  Amtsgericht Frankfurt  Carolien Nijhuis+Louis Rustenhoven]

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