Lightweight network monitoring for POSIX systems.

The nemo-core project consists of two programs - the requester and the responder - named nreq and nres respectively. The requester program periodically issues UDP datagram requests to a selected set of network targets, whereas the responder program awaits the requests and issues the appropriate responses. The datagram payload contains diagnostic information that can be used to test and monitor unicast network configuration.

In order to make the programs as reusable as possible, the decision was taken to perform no particular action upon any events - but rather provide a plugin mechanism via standard dlopen(3) mechanism of shared objects. Each program provides a different set of actions, which are executed upon the triggering. Example action sets are:

• nemo-csv
• nemo-sqlite

First step is to start the responder process

• specifying its unique key to be 123
• adding action set nemo-res-csv.so

dlo@linux$ nres \
 -k 123         \
 -a nemo-res-csv.so`

Second step is to start the requestor process:

• specifying its unique key to be 456
• adding action set nemo-req-csv.so
• setting one target: DNS name linux

dlo@freebsd$ nreq    \
  -k 456             \
  -a nemo-req-csv.so \
  linux

To build nemo-core on Linux:

dlo@linux$ make CC=gcc
dlo@linux$ make install

To build nemo-core on FreeBSD:

dlo@freebsd$ make CC=clang FTM= 
dlo@freebsd$ make install

The project aims at supporting 32-bit and 64-bit architectures, Linux, FreeBSD, NetBSD, and OpenBSD operating systems and all major C compilers, e.g. gcc and clang. If any combination of the above does not work, please feel free to notify the project maintainers and/or submit a patch.

The nreq and nres programs are documented via standard UNIX manual pages, located in the man/ directory. Both manual pages belong the section 8 of the manual. The make install command copies the manual page files to the standard system location. All reasonable distributions of the software suite should have the manual pages bundled in.

The codebase is written in pure C99 while being fully compliant with the POSIX.1-2018 interfaces. All further code contributions must adhere to these standards.

One of the main implementation goals was to create programs that use the minimal possible resources. This is reflected in both file descriptor, and memory usage. Both programs use a constant amount of memory and only two open sockets at any time. No dynamic allocation is performed by either program throughout the whole lifetime of both processes.

Certain trade-offs were part of the design and implementation of the programs. The main limitation throughout the software suite is the upper bound of number of targets supported in each requester process: 512. The second main limitation is the number of actions sets attachable to a single process: 32.

The nemo-core project is licensed under the terms of the 2-cause BSD license.

Daniel Lovasko daniel.lovasko@gmail.com