SLA monitoring

OK, this is what I need. I have 10 networks(vlans)

(mask 255.255.0.0)
10.50.x.x
10.51.x.x
10.52.x.x
10.53.x.x
10.54.x.x
10.55.x.x
10.56.x.x
10.57.x.x
10.58.x.x
10.59.x.x


There are thousands of devices on each vlans. I need be able to monitor all the devices on each vlan. I just want to be able to PING to see if its up or down. If on any vlan, 30% nodes are down, send me a alert via email.

Also, if I can pull historic graphs by vlans, that would be swell.

I know there is intermapper, solarwinds etc., but looking for freeware/shareware.

thanks

Free:
http://www.nagios.org/

Not quite free but awesome:
http://www.hybodus.com/



-Maestr0

See the Tools section in www.snmplink.org .

Peace always,
<jdenny>