Count Events by ICMP

This DTrace one-liner count events by ICMP:

# dtrace -n 'icmp:::send,icmp:::receive { @i[icmp_type_string[args[4]->icmp_type]] = count(); }'
dtrace: description 'icmp:::send,icmp:::receive ' matched 25 probes
^C

 Echo reply                                                        7
 Echo request                                                      7