TCP port 102 is the standard network port used by Siemens S7 communication, the protocol many industrial controllers use for engineering, diagnostics, and read/write access. In practice, this port is a direct exposure point for PLCs and related automation systems, so it should never be treated like an ordinary service port.
Security teams care about port 102 because reachable S7 services can allow reconnaissance, state reading, and in some cases unauthorized changes to controller data or logic. Attackers often look for it during internet scanning or after gaining access to a nearby workstation or remote session. Defenders use segmentation, allowlisting, authentication, and logging to reduce risk, and they monitor unusual traffic on port 102 as a sign that a controller may be exposed or being probed.