Security > "Snmp - Siemens SIMATIC S7-400 Operating Instructions Manual

NTP configuration
You will find help on the parameters in the STEP 7 information system.
● NTP server
You configure the NTP servers in the table of NTP servers.
If you use "NTP (secure)", the servers of the type NTP (secure) that you configured in the
global security settings are also displayed here.
● Accept time from non-synchronized NTP servers
If the option is enabled, the CP also accepts the time-of-day from non-synchronized NTP
servers with stratum 16.
If the option is disabled, the response is as follows: If the CP receives a time-of-day frame
from an unsynchronized NTP server with stratum 16, the time of day is not set according
to the frame. In this case, none of the NTP servers is displayed as "NTP master" in the
diagnostics; but rather only as being "reachable".
Setting the SYA bit when synchronizing via NTP
If the time is forwarded to the CPU, with each time frame the CP sets bit 0 of the time status
word (SZL-ID 132, index 8). The status bit indicates on the CPU whether the time is
synchronized with the external time master.
If you evaluate the time status using SFC 51 "RDSYSST", configure a synchronization cycle
shorter than 3 minutes. This avoids the status bit being reset cyclically by the CPU after 3
minutes if NTP servers are unreachable or not synchronized.
4.8.8 Security > "SNMP"
SNMP
The range of functions of the CP for SNMP can be found in the section SNMP (Page 120).
If the security functions are enabled, you have the following selection and setting options.
SNMP
● "Enable SNMP"
If the option is enabled, communication via SNMP is released on the device. As default,
SNMPv1 is enabled.
If the option is disabled, queries from SNMP clients are not replied to either via SNMPv1
or via SNMPv3.
● "Use SNMPv1"
Enables the use of SNMPv1 for the CP. For information on the configuration of the
required community strings see below (SNMPv1).
● "Use SNMPv3"
Enables the use of SNMPv3 for the CP. For information on the configuration of the
required algorithms see below (SNMPv3).
CP 443-1 OPC UA
Operating Instructions, 01/2017, C79000-G8976-C427-02
4.8 Configuration of the CP in STEP 7 Professional
Configuration and operation
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