DHCP Option 43 Configuration Help For OES DNS/DHCP Management Console

  • 7009148
  • 09-Aug-2011
  • 27-Apr-2012

Environment

Novell Open Enterprise Server 2 (OES 2) Linux Support Pack 3
Novell DNS/DHCP Java Management Console
Novell iManager
Novell DHCP
Novell DNS

Situation

DHCP Option 43 is the option used for vendor-specific information.  Novell's iManager and DNS/DHCP Management Console make it a powerful option to configure, but it can be confusing to setup.  This document is intended to point the inquirer to a  high-level, brief overview, and provide a working example.  As vendor-specific information is just that, vendor-specific, it is not practical to give an example for every conceivable scenario.  Further examples may be added over time to help clarify this topic.

Resolution

The vendor-specific information should be provided by the vendor as to what their clients are looking for.  More detailed information about DCHP option 43 and vendor-specific information can be found here:
 
EXAMPLE:

The ACME vendor has provided their customer with a particular string that needs to be passed from DHCP to its clients.  Each vendor is identified by a vendor string.  In this case it is "Access Point AP300". The other string to be used as a value for option 43 is "192.168.2.15,192.168.2.73" without quotes.  This string containing two IP addresses separated by a comma must first be changed into HEX.

The string 192.168.2.15,192.168.2.73 in hex is: 31:39:32:2e:31:36:38:2e:32:2e:31:35:2c:31:39:32:2e:31:36:38:2e:32:2e:37:33

Notice that we don't convert the 192 into a hex value, but instead we need to convert the 1, then the 9, then the 2, then a period...

31 = 1, 39 = 9, 32 = 2, 2e = .(period), and so on...
At the end of the first IP address you will notice a 2c which is the comma, followed by the IP address in hex as before.

If the above HEX string were to be placed into the value field of option 43 as-is, the value would be incomplete and would fail to work properly. The missing, needed information is the value 2b, which represents option 43, and a HEX value representing the length of the above HEX string. To come up with your specific length, count out the number of HEX entries in your string. In this example the length is 25 (decimal) or 19 in HEX.  The length is then appended onto the option (2b), and then the value appended to it ( the length (19) ).  The result is as follows:

2b:19:31:39:32:2e:31:36:38:2e:32:2e:31:35:2c:31:39:32:2e:31:36:38:2e:32:2e:37:33

DHCP OPTION 43 can be represented as a decimal 43, or as a HEX 2b

2b is the value that should be utilized for option 43 in our example followed by the HEX 19 length.
 
A restart of DHCP is required for this configuration change to take effect. 
A review of the /var/log/dhcp-ldap-startup.log file will show whether or not DHCP correctly read this configuration change.
 
 

Additional Information

Due to the fact that option 43 is vendor-specific, and Novell doesn't have any control over what a vendor will include in their specific implementation of option 43, Novell made the global DHCP option 43 a HEX string.  For example, for each vendor there can be a private table of DHCP options which is kept separately by the DHCP server. These options can be numbered similarly to the main DHCP options but the numbers refer to the vendor's private options table. Vendors can reuse numbers that are already used for global options for private options with a completely different meaning.  For this reason the HEX string must have the option and length explicitly declared at the beginning of the HEX string. 

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