What does a port -1 mean? Home › Forums › What does a port -1 mean? This topic contains 0 replies, has 1 voice, and was last updated by BrianMiz 1 week, 5 days ago. Author Posts November 7, 2019 at 2:14 am #155631 BrianMizMember I’m doing a lab in which i’m inspecting an ICS pcap file using grassmarlin. I have a private ip going to a multicast address and the source/destination port is -1. The protocol is -1 too. Can someone explain what this means? Author Posts You must be logged in to reply to this topic.