Assignment of an IP address
4.3 Address assignment with DHCP
SCALANCE W780/W740 to IEEE 802.11n Web Based Management
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Configuration Manual, 03/2015, C79000-G8976-C267-08
4.3
Address assignment with DHCP
Properties of DHCP
DHCP (Dynamic Host Configuration Protocol) is a method for automatic assignment of IP
addresses. It has the following characteristics:
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DHCP can be used both when starting up a device and during ongoing operation.
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The assigned IP address remains valid only for a limited time known as the lease time.
Once this period has elapsed, the client must either request a new IP address or extend
the lease time of the existing IP address.
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There is normally no fixed address assignment; in other words, when a client requests an
IP address again, it normally receives a different address from the previous address. It is
possible to configure the DHCP server so that the DHCP client always receives the same
fixed address in response to its request. The parameter with which the DHCP client is
identified for the fixed address assignment is set on the DHCP client. The address can be
assigned via the MAC address, the DHCP client ID or the system name. You configure
the parameter in "System > DHCP Client (Page 166)".
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The following DHCP options are supported:
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DHCP option 6: Assignment of a DNS server address
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DHCP option 66: Assignment of a dynamic TFTP server name
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DHCP option 67: Assignment of a dynamic boot file name
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DHCP option 82: Assignment of IP addresses depending on the switch port or the
VLAN ID
Note
DHCP uses a mechanism with which the IP address is assigned for only a short time
(lease time). If the device does not reach the DHCP server with a new request on expiry
of the lease time, the assigned IP address, the subnet mask and the gateway continue to
be used.
The device therefore remains accessible under the last assigned IP address even without
a DHCP server. This is not the standard behavior of office devices but is necessary for
problem-free operation of the plant.