How exactly does your temperature monitor work?

We have a temperature monitor graph with history information. How do we do it?

The usual way to monitor temperature is to use SNMP (simple network management protocol) to obtain it from some device that is measuring the temperature and that is making it available via SNMP. One problem with this is that SNMP isn't very secure. It uses a simple "community string" to authenticate the user. And recent studies have found security flaws in some implementations of SNMP.

Our way of dealing with this is that our SNMP devices have all been placed behind a firewall that blocks the SNMP ports. So only someone inside our firewall would get anywhere trying to guess the community strings. In addition, our SNMP devices don't have fully routable IP addresses but only have non-routable IP addresses, which also keeps out outsiders. SNMP passes community strings in the clear, so packet sniffing from within our firewall would pretty quickly obtain the community strings. But we assume that persons within our firewall can be trusted. (Persons within our firewall could take a sledgehammer to the DSLAM I suppose, saving the trouble of guessing the community string.)

We suspect that our DSLAM itself (a Copper Mountain CE-150) probably has a temperature sensor inside, that could be interrogated via SNMP to allow us to monitor its internal temperature. But we can't find it in the MIB provided by the manufacturer.

Our UPS (an APC Smart-UPS RM) has a card slot which can receive one accessory card. In our case we wanted to add two accessory cards, so we had to add an external expansion chassis to hold the second card. The expansion chassis holds our Web/SNMP Management Card, while the UPS card slot is used for our temperature/humidity card. The web/SNMP card is pretty neat. It obtains all of the SNMP information from the UPS and from the temperature/humidity card and makes it available to our SNMP system. It has an ethernet port which we connect to the ethernet port on the DSLAM (on the system control module of the DSLAM). The Web/SNMP card also has outgoing email capability to send email to us to annunciate any of a number of conditions. For example, the temperature/humidity card also has switch contacts so that if anyone tampers with the DSLAM cabinet or the protector cabinet, a text page is sent. When the UPS does a self-test (as it does every two weeks) the results are text-paged. If the UPS goes into battery mode (due to power failure) then this event is text-paged.

The Web/SNMP card also provides a web server which we use for configuring and controlling the UPS and the temperature/humidity card.

The Web/SNMP card has a street price (new) of $216; we got it on eBay for $120. The expansion chassis has a street price of $50; we got it on eBay for $15. The temperature/humidity card has a street price of $132; we got it on eBay for $60.

As it turns out, our UPS has an internal temperature sensor. The SNMP address for this temperature is 1.3.6.1.4.1.318.1.1.1.2.2.2.0. The temperature as measured by the temperature/humidity card is at 1.3.6.1.4.1.318.1.1.2.1.1.0. We use MRTG to graph the temperature information.