[j-nsp] understanding interface traffic counters of Juniper router

[Martin T]

I made a following setup:

http://img4.imageshack.us/img4/9311/switchvsroutertraffic.png

"Setup with Juniper router" uses Juniper router and "Setup with Cisco
router" uses Cisco router. Both computers sent data(Iperf sends 1470
byte datagrams) for 300 seconds at 9Mbps. As you can see, in case of
Cisco router and switch, the difference is 0.3%(actually I did
multiple tests with different bandwidth values and test lengths and
difference was always 0.3%). In case of Juniper router, the difference
between Cisco switch interface traffic counters and Juniper router
interface traffic counters were 1.2% - 1.3%.

What might cause this 0.3% difference in case of Cisco router and
Cisco switch? What might cause 1.2% - 1.3% difference in case of
Juniper router and Cisco switch? Is Cisco switch counting L2 header as
well and Juniper router counts only upto IP header? If yes, then this
1.2% - 1.3% difference is logical..


regards,
martin