Description:

This article describes how network devices, which obtain their IP address via DHCP can be assigned additional information besides the usual IP parameters via a DHCP option.

For a list of the most common DHCP options see RFC 2123.





Requirements:


Procedure:
1) Open the router configuration in LANconfig and go to the menu IPv4 → DHCPv4 → DHCP options.
Screenshot of a DHCP client configuration interface showing options to apply DHCP server settings to selected networks, alongside fields for setting DHCP options, managing leases with RADIUS accounting, and general network parameters.
2) Create a new entry and modify the following parameters as needed:
  • Option number: Enter the code number of the DHCP option.
  • Sub-Options-Number: Optionally you can enter a Sub-Option-Number. For instance this is used in the DHCP option 43 to inform the connected SIP telephones where they can get the firmware and the configuration.
  • Vendor-Class-Mask: Optionally you can enter a Vendor-Class-Mask. The DHCP option is only sent when the network device sends a DHCP request with the string contained in the mask. It is possible to use the wildcards * (any number of characters) and ? (exactly one character). For LANCOM devices the string *LANCOM* would be used.
  • User-Class-Mask: Optionally you can enter a User-Class-Mask ein. The DHCP option is only sent when the network device sends a DHCP request with the string contained in the mask. It is possible to use the wildcards * (any number of characters) and ? (exactly one character). For LANCOM devices the string *LANCOM* would be used.
  • Network name: In the dropdown menu select the DHCP network where the DHCP option should be assigned.
  • Type: In the dropdown menu select the Type which fits the selected DHCP option.
    • String (default setting)
    • IP address
    • 32 bit integer
    • 16 bit integer
    • 8 bit integer
  • Value: Enter the Value which fits the used DHCP option and the selected Type. For example, this could be an IP address or a URL.
  • Append Sub-Option: If the DHCP option 43 is used and a Sub-Options-Number should be appended, the option Yes has to be selected. The Sub-Options-Number with the corresponding information then has to be entered in a separate entry. Thereby the entries are bundled.

Image displaying a partial view of a technical user interface with unclear text and configuration options.



Examples for DHCP options:
DHCP option 6 - Domain Name Server Option:
  • Option number: Enter the number 6.
  • Network name: In the dropdown menu select the DHCP network, where the DHCP option should be assigned (in this example the network INTRANET).
  • Type: In the dropdown menu select the type IP address.
  • Value: Enter the IP address of a DNS server (in this example 192.168.10.200). If two DNS servers should be entered, these can be separated via a comma (e.g. 192.168.10.200, 217.137.150.33).
Image showing a partially visible tech-related user interface with labels and types related to IP addressing configurations.

DHCP option 17 - Rootpath:
  • Option number: Enter the number 17.
  • Network name: In the dropdown menu select the DHCP network, where the DHCP option should be assigned (in this example the network INTRANET).
  • Type: In the dropdown menu select the type String.
  • Value: Enter the URL for the path to the root disk.
Image displays a partial view of a technical user interface with unclear text, possibly representing options or settings.

DHC option 42 - Network Time Protocol Servers Option:
  • Option number: Enter the number 42.
  • Network name: In the dropdown menu select the DHCP network, where the DHCP option should be assigned (in this example the network INTRANET).
  • Typd: In the dropdown menu select the type IP address or String.
  • Value: Enter the IP address of a time server or the DNS name of a time server.
Image of a partial and blurred technical configuration interface with the text mentioning 'Type IP address' and other obscured options.  Image shows a fragmented or unclear view of a technical user interface or configuration menu with partially readable options and settings.

DHCP option 44 - NetBIOS over TCP/IP Name Server Option:
  • Option number: Enter the number 44.
  • Network name: In the dropdown menu select the DHCP network, where the DHCP option should be assigned (in this example the network INTRANET).
  • Type: In the dropdown menu select the type IP address.
  • Value: Enter the IP address of a NetBIOS server.
The image shows a partially visible technical configuration menu with options related to IP address settings.

DHCP option 66 - TFTP server name:
  • Option number: Enter the number 66.
  • Network name: In the dropdown menu select the DHCP network, where the DHCP option should be assigned (in this example the network INTRANET).
  • Type: In the dropdown menu select the type IP address or String.
  • Value: Enter the IP address of a TFTP server or the DNS name of a TFTP server.
Image showing a partial view of a technical configuration screen with obscured and incomplete text, including a mention of Type IP address. Image of a partially visible technical user interface with miscellaneous text elements and option titles.

DHCP option 121 - Classless Static Route:
The procedure is described in the following Knowledge Base article:
Configuring DHCP option 121 (classless static route) in the LANCOM router

DHCP option 252 - Web Proxy Auto-Discovery Protocol:
  • Option number: Enter the number 252.
  • Network name: In the dropdown menu select the DHCP network, where the DHCP option should be assigned (in this example the network INTRANET).
  • Type: In the dropdown menu select the type String.
  • Value: Enter the URL of the web server with the proxy configuration (in this example http://server.intern/proxyconfig.pac ).
Image showing a blurry or unclear text possibly from a technical user interface or configuration menu.

Specify an image file for a PXE boot server:
1) Go to the menu IPv4 → BootP → Boot images.
Screenshot of a network configuration interface showing BOOTP settings for assigning fixed addresses and specifying boot images for connected stations.
2) Create a new entry and modify the following parameters:
  • Designation: Enter a descriptive name for the boot image.
  • Server address: Enter the IP address of the server, which provides the boot image.
  • File name: Enter the name of the file on the server, which contains the boot image.

Image displaying a partial view of a technical diagram, highlighting the labels 'Feo', 'Fenone', and 'Cea'.

3) Go to the menu IPv4 → BootP → Stations.
Screenshot of a technical configuration interface displaying settings for DHCP, BOOTP, and options to assign fixed addresses and specify boot images for network stations.
4) Create a new entry and modify the following parameters:
  • Station MAC address: Enter the MAC address of the PXE client in the format 00:a0:57:12:34:56.
  • Network name: In the dropdown menu select the Network, from which an IP address should be assigned to the network device.
  • IP address: Enter the IP address, which should be assigned to the network device.
  • Station name: Optionally you can enter a descriptive name for the station.
  • Boot image: In the dropdown menu select the boot image created in step 2.

Screenshot of a network configuration menu displaying options for selecting a network named INTRANET and a boot image labeled BOOTIMAGE.

 

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