Entry type: FAQ, Entry ID: 49588330, Entry date: 05/16/2011
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Which Industrial Ethernet CPs support the DHCP Option 12 (Host Name) and how do you configure the DHCP Option 12?

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Description
The Dynamic Host Configuration Protocol (DHCP) permits you to assign the network configuration to clients by means of a server.
The Dynamic Host Configuration Protocol was defined in the RFC 2131 and was assigned UDP ports 67 and 68 by the Internet Assigned Numbers Authority.

The various DHCP options are defined in the RFC2132.

DHCP Option 61 (Client Identifier)
The Industrial Ethernet CPs support the DHCP Option 61 (Client Identifier).

The DHCP Option 61 (Client Identifier) is used by DHCP clients to identify themselves uniquely on a DHCP server. This means that DHCP servers can trace the assignment of IP addresses and network administrators can thus also reserve addresses for specific interfaces. Therefore, within an administrative domain, unique values are also expected for all DHCP clients. Normally, the Client Identifier is the MAC address of the network interface card. However, for Industrial Ethernet CPs you can also manually enter the Client Identifier for each interface with DHCP support so that when you replace a CP, the same reserved IP address can be retained. In the case of some DHCP servers, however, the Client Identifier can also be used to register the assigned IP address on a DNS server.

For the Industrial Ethernet CPs the DHCP Option 61 is configured in the Hardware Configuration of STEP 7.

In the Hardware Configuration you double-click the PROFINET interface of the Industrial Ethernet CP to open the "Properties" dialog of the PROFINET interface.
Switch to the "IP Configuration" tab to enable the "Obtain IP address from a DHCP server:" option and enter the Client ID.


Fig. 01

DHCP Option 12 (Host Name)
For DHCP servers that require a host name for registering the IP address assigned to the Industrial Ethernet CP on the DNS server, the Industrial Ethernet CPs below support the DHCP Option 12 (Host Name):

  • CP343-1 Advanced (6GK7343-1GX30-0XE0 as from firmware V1.2)
  • CP343-1 Standard (6GK7343-1EX30-0XE0 as from firmware V2.4)
  • CP343-1 Lean (6GK7343-1CX10-0XE0 as from firmware V2.4)

Proceed as follows to configure the DHCP Option 12.
 

No. Procedure
1 In the Hardware Configuration of STEP 7 you double-click the PROFINET interface of the Industrial Ethernet CP to open the "Properties" dialog of the PROFINET interface.
Switch to the "IP Configuration" tab to enable the "Obtain IP address from a DHCP server:" option.

Note:
Optionally you can also enter the Client ID, in other words, assign the Client Identifier.


Fig. 02

2 Load the hardware configuration into the CPU.
Then the Industrial Ethernet CP requests its IP address based on its MAC address or an optionally assigned Client Identifier for a DHCP server. The SysName is not yet set in this phase and therefore cannot yet be transferred to the DHCP server so that it can register the assigned IP address together with the SysName as host name for the DNS server.
3 If the IP address has been assigned successfully to the Industrial Ethernet CP, the administrator must use exactly this IP address to set the SysName in the Industrial Ethernet with an SNMP Management Tool.
4 As from the next DHCP request, like DHCP DISCOVER or DHCP REQUEST, for example, in the case of Lease Time Extension or restart, the Industrial Ethernet CP then always transfers the SysName as Host Name to the DHCP server.

Note
In the case of Advanced CPs the SysName is stored in the C-PLUG. When you change a module, the SysName is retained if the old C-PLUG is slotted into the new module.
In the case of Lean and Standard CPs the SysName is stored in the onboard flash, in other words, when you change a module, you have to set the SysName anew.