DYNAMIC INTERNET GATEWAY PLUGIN FOR olsr.org olsrd
by Andreas Tønnesen(andreto@olsr.org)
addittions by Jens Nachitgall

21.12.2004
  bjoern Riemer
- added universal hna checking
  the plParams are parsed in spechial order, first the HNA parameter syntax: "net mask"
  the following Ping parameter are only used for the previus HNA entry.
  if there is no previus HNA entry then HNA "0.0.0.0 0.0.0.0" for internet GW is assumed

30.11.2004

  updates by Jens:

- Upgraded to confirm with v2 plugin interface
- removed IPC stuff
- Removed much unnessecarry stuff
- Added an optional validation based on the ping command, which caused
  some internal restructuring, e.g. the dependency of a threading
  library)
- the config file accepts an "Interval", meaning how often the check is
  done

HOW TO USE

Add an entry like this to your olsrd configuration file:

LoadPlugin "olsrd_dyn_gw.so.0.4"
{
    # how often to look for a inet gw, in seconds
    # defaults to 5 secs, if commented out
    PlParam     "Interval"   "40"
    
    # if one or more IPv4 addresses are given, do a ping on these in
    # descending order to validate that there is not only an entry in
    # routing table, but also a real internet connection. If any of
    # these addresses could be pinged successfully, the test was
    # succesful, i.e. if the ping on the 1st address was successful,the
    # 2nd won't be pinged
    PlParam     "Ping"       "141.1.1.1"
    PlParam     "Ping"       "194.25.2.129"
    PlParam	"HNA"	"192.168.80.0 255.255.255.0"
    PlParam	"HNA"	"192.168.81.0 255.255.255.0"
    PlParam	"Ping"	"192.168.81.12"
}


ABOUT

Plugin is IPv4 only and it only runs on Linux with the libpthread
library installed!

This is a plugin that checks if the local node has a Internet-
connection. A Internet-connetion is identified by a "default gw" with a
hopcount of 0. That is a route to 0.0.0.0/0 with metric 0.  By default
the check is done every 5 secs. You can change the check interval by
providing an value for "Interval" in the plugin's section of olsrd.conf.

If one or more IPv4 addresses are given as values for "Ping" in the
section or dyn_gw in olsrd.conf, then a test is done to validate if
there is really an internet connection (and not just an entry in the
routing table). If any of the arbitrary many given IPv4 addresses can be
pinged, the validation was successful. The addresses are pinged in the
order given in the olsrd.conf (i.e. the first given address is pinged
first, the the 2nd, and so on). For this to work a command like 
"ping -c 1 -q <PING-ADDRESS>" must be possible on the system olsrd runs
on. The validation is based on the return value of this ping command.

Since OLSR uses hopcount/metric on all routes this plugin will
not respond to Internet gateways added by olsrd.

When a Internet gateway is discovered - this node will start
announcing 0.0.0.0/0 connectivity by HNA messages flooded into
the OLSR network. If the route is removed the HNA messages
will not be transmitted. This check is totally dynamic and
Internet connectivity might come and go.

This plugin will work very good with a automatic network cable
detection daemon such as  netplug:
http://freshmeat.net/projects/key-netplug/

This plugin is a good example of using plugins for other stuff
than packet transmission.