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Industrial Protocols

Siemens S7 Communication

PUT/GET, ISO-on-TCP (port 102), and data exchange between Siemens CPUs.

OT NetworkPLCSiemens · Vendor knowledge center

Overview

S7 communication is Siemens' native CPU-to-CPU and engineering protocol over ISO-on-TCP (port 102), powering PUT/GET data exchange and TIA connectivity.

Engineering purpose

Direct data exchange between Siemens controllers and access for engineering and HMI systems without intermediate servers.

How it works

PUT/GET reads and writes partner data blocks by absolute address over established connections; the served CPU must explicitly permit partner access; non-optimized DBs provide the stable absolute layout legacy clients require.

  • S7 communication runs over ISO-on-TCP, port 102; firewalls between cells must pass it explicitly.
  • PUT/GET must be enabled in the partner CPU's protection settings — modern firmware disables it by default.
  • Absolute-address access requires non-optimized DBs on the served side; optimized blocks break legacy clients.

Common faults

PUT/GET disabled by default on modern firmware blocking legacy partners; firewalls silently dropping port 102 between cells; optimized DBs breaking absolute-address clients; connection-resource exhaustion on busy CPUs.

Diagnostic checks

  1. 1Test reachability of port 102 from the client segment before debugging program logic.
  2. 2Confirm the target DB is non-optimized and PUT/GET is permitted on the partner CPU.
  3. 3Test TCP reachability of port 102 from the client segment before touching any program logic.

Safety notes

Enabled PUT/GET is unauthenticated memory access to the CPU — pair it with strict network segmentation and treat it as a controlled interface.

Commissioning notes

Document every S7 connection (partners, DBs, direction), verify firewall rules pass port 102 where required and block it everywhere else.

Related concepts

ISO-on-TCP, PUT/GET access control, optimized vs non-optimized DBs, connection resources, cell firewalls.

s7 communication · put/get · put get · iso-on-tcp · port 102 · ارتباط اس‌هفت

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When Hermes Brain uses this article

Cited for Siemens CPU-to-CPU data exchange failures, PUT/GET permission issues, and port-102 connectivity through firewalls.

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