It is very difficult to monitor unmanaged switches out of the box. From a fundamental perspectives, a switch needs to be SNMP capable, allow access to the switch community strings and have the port mirroring capability and physically present on the network with an IP address. Unmanaged switches may not have those capabilities which pose a problem. However, some switch manufacturers have proprietary tools to have some monitoring capabilities available -- but the monitoring capabilities are limited.

One way you can do this is to monitor the ethernet links itself that converge into the switch i.e. with a network tap. So if you picture it, the network tap will be installed between the switch and the end device; where you can hook up a packet tracer or protocol analyzer directly to the tap itself. The tap will then act as a passive device which just looks at the traffic going by. Being a *dumb* device, what the tap is going to report is unaltered packets without delays, jitter or distortion and is non filtered regardless of error type, IP version, size, and bandwidth. One of the drawbacks with this is that you might be introducing an extra point of failure on the network (so choose your tap manufacturer carefully as some offer added fail safe functionality) and you would have to break the network activity to install it/ take it off the network (not ideal if the network needs to be up all the time).

Most unmanaged industrial Ethernet media converters and switches include a dry contact relay output. At least all of Transition Networks' industrial products do, and this is common in the industry. Those dry contacts can be connected to the input of a local alarm light or buzzer or alarm system. The alarm system could provide remote notification by monitoring the dry contacts. Telephone or cellular autodialers are one type of alarm system that could monitor the contacts then alert someone offsite/remotely. Microtel, Inc, (www.microtel-inc.com) provides several different models of land-line or cellular-based autodialers with dry contact inputs, for example.