Siemens SIMATIC ET 200AL, System Manual

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Addressing via DHCP
10.1 Principle of address assignment via DHCP
Communication
Function Manual, 05/2021, A5E03735815-AJ
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10.1 Principle of address assignment via DHCP
Requirement configuration
The following requirements must be met so that a PROFINET interface of the S7-1500 CPU
can obtain IP address parameters via a DHCP server:
•
The address assignment via a DHCP server is configured.
Activate DHCP (Page 368)
• No PROFINET IO communication may be configured for the interface.
Principle of DHCP address assignment
The process begins as soon as the project is loaded into the CPU or the CPU is switched on
with configured DHCP address assignment and started up, the process of DHCP assignment
begins:
DHCP Discover The DHCP client searches for a suitable DHCP server via broadcast. The DHCP client
identifies itself to the DHCP server with the configured client ID or with its MAC ad-
dress.
DHCP Offer The DHCP server offers the DHCP-client IP address parameters (IPv4 address, subnet
mask, optional default router) and if necessary further data (options).
DHCP Request The DHCPclient requests the IP address parameters and options offered in the DHCP
offer.
The DHCP client of the S7-1500 CPU always accepts the first DHCP offer of a DHCP
server that meets the requirements (IP address with subnet mask).
DHCP Acknowl-
edgment
The DHCP server confirms and transmits the IP address parameters and options of-
fered in the DHCP offer.
The DHCP server also notifies the DHCP client how long the DHCP client can use the
address parameters (lease time).
Figure 10-2 Principle of address assignment with DHCP
The IP address parameters and options are stored in the load memory of the CPU. After a
general reset or restart of the CPU, the IP address parameters and options are obtained again
via DHCP.