that is a good question, I do not know the answer either. If I remember correctly, older EXOS versions (15.1, 15.3) allowed capture of traffic hitting the CPU only. The interface name used for this contained "bcm", I think.
The GTAC Knowledge article mentioned above pertains to EXOS 15.4 and later and uses EXOS front-port names.
Looking forward to an authoritative answer. 🙂
BTW there is an article to capture management port traffic as well: How do i take a packet capture of the management port?