I've been doing some reading on SNMP and its applications to monitoring and have made some useful discoveries.

SNMP (Wikipedia entry here, pretty good, and there's a good SNMP tutorial here) is an old protocol based on command/response and async alerts called 'traps.' Its insecure (based on a secret string called a 'community') up until version 3, but inside a firewall its simple, fast and very well suited to network monitoring.

In a gradual change from yesteryear, most consumer-grade network gear includes SNMP now, to my surprise. Linksys and Apple Airport are what I had on hand to experiment with, so I've got those setup and working.

Once you've got SNMP enabled on your network devices, you need software to poll them and display the results. I tried snmpd, MRTG and finally Cacti. Of them, I prefer Cacti - it's purely web-based and very easy to setup and use. It can monitor anything SNMP, local Unix variables like system load, and has nice extensibility and access control. I was also able to easily monitor random hosts by pings.(ICMP, TCP or UDP)

One problem with cacti is that it seems to only poll, and can't easily receive SNMP traps sent upon problems. Hmm. Also, adding new SNMP queries is complex; I had expected that you could add a MIB file and have it parse, but not so.

I just pinged the Inca developer, Shava Smallen, and it can hook into SNMP via an external command. Not sure if that'd require code or not.

You can see my test deployment at http://www.phfactor.net/cacti

Username and password are guest / guest