212 Fieldbus Communication
WAGO-I/O-SYSTEM 750
750-880, 750-880/025-000 ETHERNET Programmable Fieldbus Controller
Manual
Version 1.0.1
Because of this time dependency, DHCP is also used to dynamically assign
available IP addresses through client leases (lease time after which the client
requests a new address) where each DHCP client address is saved temporarily in
the server database.
In addition, DHCP clients do not require a system restart to rebind or renew
configuration with the DHCP server. Instead, clients automatically enter a
rebinding state at set timed intervals to renew their leased address allocation with
the DHCP server. This process occurs in the background and is transparent to the
user.
There are three different operating modes for a DHCP server:
•
Manual assignment
In this mode, the IP addresses are permanently assigned on the DHCP server
to specific MAC addresses. The addresses are assigned to the MAC address
for an indefinite period.
Manual assignments are used primarily to ensure that the DHCP client can
be reached under a fixed IP address.
•
Automatic assignment
For automatic assignment, a range of IP addresses is assigned on the DHCP
server.
If the address was assigned from this range once to a DHCP client, then it
belongs to the client for an indefinite period as the assigned IP address is
also bound to the MAC address.
•
Dynamic assignment
This process is similar to automatic assignment, but the DHCP server has a
statement in its configuration file that specifies how long a certain IP
address may be "leased" to a client before the client must log into the server
again and request an "extension".
If the client does not log in, the address is released and can be reassigned to
another (or the same) client. The time defined by the administrator is called
Lease Time.
Some DHCP servers also assign IP addresses based on the MAC address,
i.e., a client receives the same IP address as before after longer network
absence and elapse of the Lease Time (unless the IP address has been
assigned otherwise in the mean time).
DHCP is used to dynamically configure the network parameters.
The ETHERNET TCP/IP fieldbus controller has a DHCP client that supports the
following options in addition to the default "IP address" option:
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