Clock Functions - Siemens S7-1200 System Manual

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Extended instructions

8.1 Date, time-of-day, and clock functions

Clock functions

If an attacker can access your networks through Network Time Protocol (NTP)

synchronization, the attacker can possibly take limited control of your process by shifting

the CPU system time.

The NTP client feature of the S7-1200 CPU is disabled by default, and, when enabled, only

allows configured IP addresses to act as an NTP server. The CPU disables this feature by

default, and you must configure this feature to allow remotely-controlled CPU system time

corrections.

The S7-1200 CPU supports "time of day" interrupts and clock instructions that depend upon

accurate CPU system time. If you configure NTP and accept time synchronization from a

server, you must ensure that the server is a trusted source. Failure to do so can cause a

security breach that allows an unknown user to take limited control of your process by

shifting the CPU system time.

For security information and recommendations, please see our "Operational Guidelines for

Industrial Security"

security/Documents/operational_guidelines_industrial_security_en.pdf) on the Siemens

Service and Support site.

(http://www.industry.siemens.com/topics/global/en/industrial-

S7-1200 Programmable controller

System Manual, 03/2014, A5E02486680-AG