In this example of show vdf-status command output, there are zero "Fragments dropped" but a high number of "Packets dropped".
# show vdf-status
Virtual DeFragmentation (VDF) statistics reported by np1:
Fragments received : 3768265
Fragments processed : 3768264
Fragments dropped : 0
Fragment queue limit : 0
Fragment overlap check : 0
Overlap protection on Head of Packet (HOP) : 0
Fragment pool depletion : 0
Packet pool depletion : 0
Invalid fragment : 0
Packets processed : 1642598
Packets dropped : 481574
The "Packets dropped" counter gets incremented when the VDF module processes an invalid fragment. After processing the invalid fragment, this counter is incremented, but the frame is still forwarded through the system. Think of this counter as an "Invalid packet" or "Invalid fragment" counter, because the packet is not dropped, it is forwarded.
An example of an invalid fragment would be receiving a fragmented IP packet with a fragment offset zero (1st fragment of packet) and then not receiving any further fragments.
The first fragment is forwarded through the system, but because no subsequent fragments of this packet are received, it is invalid, and XOS currently counts it as "Packets dropped".