Related pages: TRAP IFCSPEC, Reporters, installation

This page is written from the high-level view by system users to the low-level API needed by developers of the NEMEA Modules/Detectors and by developers of the libraries contained in the NEMEA Framework

Usage by User

The recommended installation of the NEMEA system is done as a part of STaaS collector, where Ansible is used. The installation is described in the separate page.

A default path of the installed modules is in /usr/bin/nemea/. Users can read documentation of the modules in /usr/share/doc/nemea-modules/ or /usr/share/doc/nemea-detectors/.

Each module has -h parameters to print the module’s help. The header of the help shows number of communication interfaces (IFC). All IFCs are configured at the startup of a module using -i parameter with an argument. The -i parameter is also described in the module’s help in a separate section: -h 1 or -h trap. It is also described at TRAP IFCSPEC page.

Example of help header of a module

$ /usr/bin/nemea/vportscan_detector -h
TRAP module, libtrap version: 0.11.2
Name: vportscan_detector
Inputs: 1
Outputs: 1
  Vportscan detector is a simple, threshold-based detector for vertical scans
  detection. The detection algorithm uses information from basic flow records
  (source and destination IP addresses and ports, protocol, #packets, #bytes).


This output says that vportscan_detector has 1 input IFC and 1 output IFC.

Example of a command to start the module

/usr/bin/nemea/vportscan_detector -i u:flow_data_source,u:vportscan_out

This command starts vportscan_detector. The input IFC is set to u type (UNIX socket) and flow_data_source is and identifier of the IFC. Comma is a separater of IFCs, so that the second IFC is also of u type and the identifier is vportscan_out.

Note: any input IFC can be connected to one output IFC, this can be done by specifying the same IFC type and identifier.

Note2: See TRAP IFCSPEC for more detailed information about IFC configuration and types.

Usage by Programmer

This section covers documentation of the NEMEA Framework, which is the main part of the NEMEA System shared within all NEMEA Modules and Detectors. It consists of (GitHub links):

These components are described in the following subsections.



libtrap is a library (shared object) written in C. The aim of libtrap is to provide implementation of various types of communication interfaces (IFC) that can be used by modules to send or receive data messages. A developer may choose a number of output and input IFCs.

Configuration of IFCs is given by a user (not by a developer) when a module is being started. From the developer’đ point of view, it does not matter what type of IFC is used or what parameters are used.

A developer of a module must take care of initialization and finalization of the libtrap context, however, it can be copied from an existing examples. Basically, there are two main functions of libtrap that are used by repeatedly used by a developer: trap_send() to send a message via an output IFC and trap_recv() to receive a message via an input IFC.


Public API for module developers

Internal API for developers of libtrap



UniRec is a definition of binary data representation (format) and an implementation of functions to work with it. To understand UniRec, we have to split two terms: template and message. A template is a definition of fields that are present in every message. A field is defined by name and type.

There is a list of currently used UniRec fields: Developers can easily define any field.

UniRec Field Type CPP Constant C Type Size in Bytes
char UR_TYPE_CHAR char 1
uint8 UR_TYPE_UINT8 uint8_t 1
int8 UR_TYPE_INT8 int8_t 1
uint16 UR_TYPE_UINT16 uint16_t 2
int16 UR_TYPE_INT16 int16_t 2
uint32 UR_TYPE_UINT32 uint32_t 4
int32 UR_TYPE_INT32 int32_t 4
uint64 UR_TYPE_UINT64 uint64_t 8
int64 UR_TYPE_INT64 int64_t 8
float UR_TYPE_FLOAT float 4
double UR_TYPE_DOUBLE double 8
ipaddr UR_TYPE_IP ip_addr_t 16
macaddr UR_TYPE_MAC mac_addr_t 6
time UR_TYPE_TIME ur_time_t 8
string UR_TYPE_STRING char -1 (variable size)
bytes UR_TYPE_BYTES char -1 (variable size)


Generated documentation of API for module developers



nemea-common is a collection of various functions and data structures that are generally useful in modules. There are e.g. prefix tree, B+ tree, hashing functions, hash table, …


Generated documentation of API for module developers



pytrap is a native module for Python 2 and 3 that wraps API of libtrap and UniRec. It allows writing new NEMEA modules in the Python language.

Examples can be found at


Generated documentation of Python API for module developers



The main part of pycommon is a python module report2idea for reporting alerts generated by NEMEA detectors.

There is currently no development documentation for this module.

For user documentation of the configuration of reporter modules see Reporting Modules and Alert Filtering.

Prepared Examples