ipfw bandwidth shaping

[Bikrant Neupane]

Hi I am using freebsd 4.9 with ipfw to shape b/w for my broadband clients.
I have created a 64Kbit pipe and I have configured few ips to use the pipe. ie 
more than one client share the same 64Kbit pipe.

I have been montoring the b/w utilization by using the command:
ipfw pipe show $inpipe | tail -1 | awk '{ print $6 }
ipfw pipe show $outpipe | tail -1 | awk '{ print $6 }

This is the output of ipfw pipe show $pipe_no
BKT Prot _Source IP/port_ __Dest. IP/port___ Tot_pkt/bytes Pkt/Byte Drp
  0 tcp   24.76.245.191/62165    202.79.50.55/4347  2826105 864936484 42 11232 
150386
I assumed the 6th field gives the total bytes going though the pipe.
These two commands give the bytes going through the pipe and I am using the 
values to plot the mrtg graph.
But I see b/w utilization exceeding 64Kbit. At one point it reached 93Kbit!!
Am I using wrong countres to obtain b/w utilization?? please aadvice.

with regards,
Bikrant