How we monitor DSL links

We use WhatsUp (version 7.0) to monitor many aspects of our DSL system. As mentioned in our page about monitoring, we ping each of our subscriber's routers and we annunciate a loss of IP connectivity. That is essentially a monitor at ISO layer 3. But it is also desirable to monitor at ISO layer 2, namely, to know the status of the DSL link between each DSL modem and its respective port on the DSLAM. As it turns out, this can be done using SNMP.

In WhatsUp our first step was to set up a monitor for this purpose. To do this, click on "monitor" and "monitors and services." Click the button to create a new monitor. The service name should be something easy to remember, like "DSL port status". The "service type" is "SNMP monitoring." The object ID is "1.3.6.1.2.1.2.2.1.8" which selects the DSL port status for each port. Check it for a constant value of "1," and if value matches, the port is "up."

Having created the monitor, it is then necessary to set up a monitored host for each DSL port. For the host, select the "services" category, and select the monitor (e.g. "DSL port status"). It needs an argument which is the unique identifier for the port. For example, for the first SDSL card, port 13, the argument is 104130000. (The "4" means the fourth card in the DSLAM from the top, and the "13" means port 13. Set up WhatsUp so that it generates an alert for any change of state ("up" or "down"), and have it check twice before generating the alert.