arpdetect is a perl script to detect when the network you're connected to changes, and run some commands when that happens. It does this by detecting a MAC address of some host you specify (usually a router). Actions can be re-run at a predetermined period with crond.
I needed something that detected when I was on a new network and did some stuff. Like, if I was at work, I wanted to rsync some pictures to my server there, or if I was at home, I wanted to backup my mail. Things like that. I figured the easiest way was to arping for a box I knew would always be there (like the router) and run commands at that time. Of course, you may need to re-run these commands every once and a while, so it has that support as well. Take it for a spin, let me know what you think.
Install should be pretty easy; download and install the perl modules required:
and copy the program to where you like it to be (I recommend '/usr/local/bin'). Config the thing to do stuff the way you like it in some config file (I like putting it in '/usr/local/etc/arpdetect.xml') and run it! You can do that w/ the included init.d script for RedHat, or by typing a command similar to the following:
/usr/local/bin/arpdetect -c /usr/local/etc/arpdetect.xml
If something's not quite what you expect, or need something else, or it just plain works, let me know!