I have been puzzled by this for sometime and have been trying to get to the bottom of it.
I have 2 routers connected via a 10Mb FD Ethernet link and on router 1 I am traffic shaping outbound on this link with the following config:
Policy Map SHAPE
Average Rate Traffic Shaping
CIR 64000 (bps) Max. Buffers Limit 1000 (Packets)
Bc 1280 Be 0
When I flood this link I see the following on show interface f0/0:
poc#sh int f0/0 | inc 30 second
30 second input rate 0 bits/sec, 3 packets/sec
30 second output rate 64000 bits/sec, 144 packets/sec
However on the other routers interface I see:
spray#sh int f6 | inc 30 second
30 second input rate 75000 bits/sec, 148 packets/sec
30 second output rate 0 bits/sec, 0 packets/sec
So I am confused as to why interface commands show a difference in data i.e 64Kb on the outgoing interface (poc) and 75Kb on the incoming interface (spray)?
This is a back to back connection between 2 seperate routers. (poc out connected to spray in)
And what is this 9-10 bytes per packet of unaccounted traffic?
interface counters on ethernet interfaces consider the layer2 frame without the final 4 byte FCS so the size of frame is seen as
IP size + 14 bytes (but it cannot be less then 60 bytes because ethernet frame mimimum size is 64 bytes, 1518 bytes max including FCS)
I'm sure old CAR committed access rate works taking in account L2 overhead and I think also Class based shaping and policing do the same.
Hope to help