Within data centres and telecommunications points of presence, many legacy monitoring solutions exist. The architecture is typically rack mounted hardware that has wired sensors or probes. The hardware has a built-in web server and in most cases also a text based cli. The connectivity is typically via an internal Ethernet network and optionally out of band connectivity via a GSM modem. The user is required to connect out of band to the web server or cli on the hardware. This connection entails an incoming session over the modem that requires approval from the service provider. The service provider usually discourages these type of connections due to hacking. Additionally, the network address of the hardware needs to be associated with a name resolution system and often this is a dynamic DNS type service. This architecture is the basis for many types of botnet attacks.
Read the article over at LinkedIn here.