Table of Contents
=======================================
1. Introduction
2. Building and Installing
3. Configuration File
4. Command line
5. Tools
6. References



1.   Introduction
=======================================
This application provides means to check the availability of remote hosts
through pings to them.


1.1. Rationale
---------------------------------------
The application uses ICMP echo requests messages, or TCP SYN segments, to
verify whether a given host is available (up) or not (down).

The host's address can be an IP or a DNS.


1.2. How to use
---------------------------------------
There are many ways to invoke the application, the simplest is just type:
  ./pingcheck
which uses the configuration values from the configuration file (described in
the Configuration File section).

Note: like the ordinary ping, pingcheck binary requires root privileges to
access control packets. You can run it from sudo:
  sudo ./pingcheck
or setuid:
  sudo chown root:root pingcheck
  sudo chmod u+s pingcheck
  ./pingcheck
the last method is the common way to provide temporary root privileges for
an executable.


1.3. Resources
---------------------------------------
Further information about the problem domain can be found in the References
section.


1.4. Legal Issues
---------------------------------------
Most parts are licensed under the GPLv2 + linking exception.

Parts of the ICMP code are based on the ping example found in the boost Asio
documentation ((c) Christopher Kohlhoff) but are now heavily modified. The DNS
resolver mechanism is based on boost::net::dns and is therefore licensed under
the boost license. Notes about this are included in the beginning of the source
code.


2.   Building and Installing
=======================================
After downloading the source code and necessary libraries (in particular boost)
and tools (cmake) you should be able to do:

me@my_linux_host ~/some/dir/pingcheck> mkdir build
me@my_linux_host ~/some/dir/pingcheck> cd build
me@my_linux_host ~/some/dir/pingcheck/build> ccmake ../
                                               OR
me@my_linux_host ~/some/dir/pingcheck/build> cmake ../
me@my_linux_host ~/some/dir/pingcheck/build> make help      # show more options
me@my_linux_host ~/some/dir/pingcheck/build> make
me@my_linux_host ~/some/dir/pingcheck/build> make check
me@my_linux_host ~/some/dir/pingcheck/build> make install

The default install location is /usr/local, the easiest way to change this is
through ccmake


3.   Configuration file
=======================================
In this section are described the configuration items, along with they possible
values and meanings. This section is organized in each major configuration
block. An example file is contained in the conf subdirectory.


3.1. General
---------------------------------------
This configurations are shared among and affect all the hosts.
- default-source-network-interface: the local network interface from where the
  ping packages will originate. This option is used for those hosts that set
  source-network-interface=default
- nameserver: the server which the hosts names will be resolved. It is the
  lookup server which the application will query first. If left blank or omited,
  it will use the /etc/resolv.conf.
  You can use the nslookup <host> to figure out the nameserver.
- hosts-down-limit: an absolute number, which ranges from 0 to the number of
  hosts available. This value represents the minimum number of hosts that have
  to fail (i.e. do not reply to the ping) in order to alert any external system.
- ping-fail-limit: percentage of pings to a host that can fail. If the
  percentage of failed pings to a host exceed this number, then the host is
  considered down.
- status-notifier-cmd: the command line that is called when a host is down, or
  up. Accepted variables are:
    ${status} - down or up
- link-up-interval: how long (in minutes) the pings must be returned with
  success in order to consider the link up, or stable.
- link-down-interval: how long (in minutes) the pings must fail, in order to the
  application consider the link down.
- ratio-random-hosts: expects a value in [0,1]; if <1 will only use the given
  ratio of hosts, selecting them at random
- ping-reply-timeout: Amount of time to wait for an EchoReply to an Echo Request
  before sending the next ping
- max-address-resolution-attempts: For hosts given as DNS names, will first do
  a DNS lookup to get corresponding IPs. This number specifies how often that is
  attempted before declaring the host offline
- resolved-ip-ttl-threshold: When the TTL for an IP falls below this threshold,
  a new DNS lookup will be scheduled


3.2. Host
---------------------------------------
(All these settings must always be present!)
- name: the DNS or IP of the host to ping. Take in consideration that, if a
  DNS is given, the application pings all IPs in the look up table, however, if
  IP is provide, it is the only which will be pinged.
- port: when using a port based protocol, like TCP, this field specifies in
  which port to ping the host.
- source-network-interface: the local network interface from where the ping
  packages for a given host will originate. To use the global network
  interface, specify value as "default"
- interval: the host will be pinged every "interval" seconds. Can be specified
  as fixed number (e.g. "30") or as a range (e.g. "30..60"), from which the
  interval will be picked at random (e.g. 42) at startup
- ping-protocol: indicates which protocol to use to ping the destination host,
  the currently supported protocols are TCP (tcp, tcp_ipv6) and ICMP (icmp,
  icmpv6).


4.   Command line
=======================================
The command line accepts the general configuration file options plus the
following:
- config-file: command line to specify a file where the hosts and other
  configuration information are provided.
- daemon: run the application as a daemon.
- log-level: apply a filter of which log messages will be printed. The available
  options are the default Unix levels (e.g. debug, info, etc.).
- log-output: select the place where the log messages will be printed. The
  available options are CONSOLE, TERMINAL and SYSLOG.


5.   Tools
=======================================
Along with pingcheck, the binary feed_packet_data will be built but not copied
like the pingcheck binary to the install location (you will find it in your
build_directory/src/feed_packet_data). It allows direct access to the ICMP/TCP
parser factories that interpret incoming network data. It can be fed data in
pcap format or as raw binary data, either from file or stdin.


6.   References
=======================================
[1]  http://tools.ietf.org/html/rfc792
[2]  http://en.wikipedia.org/wiki/Ping
[3]  http://en.wikipedia.org/wiki/Internet_Control_Message_Protocol
[4]  http://en.wikipedia.org/wiki/ICMPv6
[5]  http://www.boost.org/doc/libs/1_45_0/doc/html/boost_asio.html
[6]  http://www.boost.org/doc/libs/1_45_0/doc/html/program_options.html
[7]  http://www.networkuptime.com/nmap/page4-5.shtml