Q. On a router Ethernet interface connected directly to a packetshaper, InterMapper's interface stats show a particular level of multicast traffic transmitted by the packetshaper. The router interface is reporting the same level of traffic, except as broadcast.

If InterMapper uses MIB-II data for those interfaces (counters for unicast and non-unicast packets only) how is it differentiating? And why does it characterize the traffic differently?

A. When a device is polled with SNMPv2c or SNMPv3, InterMapper will automatically use the counters ifInMulticastPkts, ifInBroadcastPkts, ifOutMulticastPkts and ifOutBroadcastPkts, when those counters are available, instead of the stock ifInNUcastPkts and ifOutNUcastPkts.

It is possible that you are polling the router with SNMPv2c or above, and the packetshaper with SNMPv1. It's also possible that the packetshaper may not support the separate multicast/broadcast counter in its SNMP agent, and InterMapper has to rely on the non-unicast pkt counters alone.