Based on your last post, I am assuming that you have JUNOS with enhanced services. Monitor traffic will only see traffic to and from the RE side of the J-series. That basically means traffic destined to the router itself. You would not see transit traffic even if you were to drop to shell and use tcpdump.
You can configure packet-capture, though. This is a feature specifically for J-Series which can let you capture transit traffic in PCAP format. Refer to J-Series Administration Guide for details.