You can display statistics for a specific vif or for all vifs. These include the number of packets received and sent by each vif.
The following example displays output of the vif stat command:
vif stat vif0 vif (trunk) vif0 e3a e3b Pkts In Pkts Out Pkts In Pkts Out 8637076 47801540 158 159 1617 9588 0 0 1009 5928 0 0 1269 7506 0 0 1293 7632 0 0 920 5388 0 0 1098 6462 0 0 2212 13176 0 0 1315 7776 0 0
The first row of the output shows the total number of packets received and sent until the time the vif stat command was run, and the following rows show the total number of packets received and sent per second thereafter.