[c-nsp] difference between "multicast" and "multicasts" counters in Catalyst "sh int" output?

[Martin T]

Hi,

interface Fa0/19 on WS-C3550-24 receives various multicast frames like
VTP(dst MAC 01:00:0c:cc:cc:cc), CDP(dst MAC 01:00:0c:cc:cc:cc) and PVST(dst
MAC 01:00:0c:cc:cc:cd). Switch counts those frames as "multicast" as it
should, but besides that, it counts those as "broadcasts" as well:

SW3#sh int Fa0/19 | i multi
     Received 4071 broadcasts (0 multicast)
     0 watchdog, 4071 multicast, 0 pause input
SW3#

Is this because Ethernet switch doesn't distinguish between broadcasts and
multicasts? I mean either broadcast or multicast frame is sent out via all
ports except the port where the frame came in. Either way, I find it bit
confusing and IMHO it would be better if only FF:FF:FF:FF:FF:FF frames are
counted as "broadcasts". Last but not least, what is this "multicast"
counter with value 0?

I can see a similar behavior on Cisco 2950 series L2 switch as well:

SW4#sh int Fa0/24 | i multi
     Received 22903 broadcasts (0 multicast)
     0 watchdog, 22903 multicast, 0 pause input
SW4#


regards,
Martin