Traffic billing - L2 encap to include or not?
fvd at de.kpn-eurorings.net
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?
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
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
[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]
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