Simple Counter


Lua function called for each packet. You can use contents of the packet to create your own metering logic.


Table simplecounter

The simplecounter table attaches the onpacket(..) function to a particular protocol layer.

protocol_guid string Which protocol do you want to attach this group to?
Trisul will invoke this counter group only for packets where that protocol is present and with a pointer to the payload at that protocol
A list of common protocol GUIDs are here
onpacket function ( engine , layer ) onpacket(..) is the main function where your LUA code goes. It is called for each packet with a layer object corresponding to the protocol_guid above
flow_counter bool Optional When set to true, this counter turns into a NETFLOW_TAP mode counter. Use this if you want to use this script with NETFLOW_TAP mode processing. Default is false

A typical simplecounter table looks like the following

Function onpacket

The onpacket function is where your LUA code goes. You can inspect the packet bytes, then apply your own logic and interact with the Trisul engine.

engine An Engine object that allows you to interact with Trisul
layer A Layer object pointing to the protocol_guid you have specified

The layer parameter

This code dumps the IP header and the size of the IP layer. Once again the GUID “{0A2C724B-5B9F-4ba6-9C97-B05080558574}” represents the IPv4 protocol

simplecounter = {

  protocol_guid = "{0A2C724B-5B9F-4ba6-9C97-B05080558574}",

  onpacket = function(engine,layer)

      print("onpacket now.. layer length = "..layer:layer_bytes())

      local bytes = layer:rawbytes()


The above snippet works as follows

  • print the IP layer length via layer:layer_bytes() See Layer
  • dump the 20 byte IP header using layer:rawbytes():hexdump()

onpacket now.. layer length = 20

00000000   45 00 00 28 a3 c8 40 00 35 06 15 4a d1 d8 f9 3a    E..(..@.5..J...:
00000010   c0 a8 01 02 00 00 00 00 00 00 00 00 00 00 00 00    ................


The engine parameter

Typically the end result of your LUA processing will result in a call to one of the Engine methods.